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I have just built...

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  • Richard
    ... a hex keyboard with 17 cheap pushbuttons, a piece of perfboard. On a breadboard I also have started building a keyboard encoder. If it works, it will
    Message 1 of 30 , Jan 10, 2013
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      ... a hex keyboard with 17 cheap pushbuttons, a piece of perfboard. On a breadboard I also have started building a keyboard encoder. If it works, it will encode a full byte with just four 74LSXX ICs.´

      There is just one part that may be a hack: The last IC is an 8 bit latch. The lower four bits come from the remaining circuit amd are supposed the key that has just been pressed.

      The outputs of the lower four bits are fed pack to the upper four inputs. This way, when the signal to latch comes, the former lower bits are transfered to the upper bits.

      Data is latched at the rising edge of the clock signal, so the outputs should still have the old values. Is it a bad practice to make the propagation delay in the latch work for me in such a manner?
    • joshbensadon
      ... No, I will guess you are using a 74LS374 which is a edge triggered latch. I ve seen this configuration in a few circuits, where they will even do it 2 or
      Message 2 of 30 , Jan 11, 2013
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        --- In cosmacelf@yahoogroups.com, "Richard" wrote:
        >
        > There is just one part that may be a hack: The last IC is an 8 bit latch. The lower four bits come from the remaining circuit amd are supposed the key that has just been pressed.
        >
        > The outputs of the lower four bits are fed pack to the upper four inputs. This way, when the signal to latch comes, the former lower bits are transfered to the upper bits.
        >
        > Data is latched at the rising edge of the clock signal, so the outputs should still have the old values. Is it a bad practice to make the propagation delay in the latch work for me in such a manner?
        >

        No, I will guess you are using a 74LS374 which is a edge triggered latch. I've seen this configuration in a few circuits, where they will even do it 2 or more times to create a shift register. The JK flip-flop was meant to work this way.

        I think bad practice is to use capacitors on digital lines to create extra delays. I recently made up a sync separator and had to use a 100pf cap in the circuit to artificially create some propagation delay. I've seen this done on some old digital circuits, for example, the IMSAI 8080 front panel does this to keep one of the latches from switching on very narrow pulses.

        The only area where I would criticize bad practice, would be the crystal oscillator. I've seen a bad design that would only work with chips from one company. Drove me nuts! Because I installed a socket to test various chips and the socket added just enough capacitance to make any chip work. At first I thought it was the chips being affected by the heat. I couldn't believe a socket would add any significant amount of capacitance. So I removed the socket, re-tried the same chips and repeated the whole process twice and confirmed my observations.

        PS. Good for you to build a hex keypad using logic chips!

        Cheers,
        Josh
      • Richard
        ... Thanks! Yahoo just swallowed a lengthy reply, but that may be better this way. I will just post the schematic when I have some results. I have already
        Message 3 of 30 , Jan 11, 2013
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          > PS. Good for you to build a hex keypad using logic chips!
          >
          > Cheers,
          > Josh

          Thanks! Yahoo just swallowed a lengthy reply, but that may be better this way. I will just post the schematic when I have some results. I have already begun to set everything up on a breadboard and the little keyboard is also ready. Now I only need some more parts. I wanted a 74LS139 and they sent me a 74LS138.

          At the moment I use a 555 timer to provide a 460 Hz clock. At that slow speed any bouncing of the keys should just go unnoticed, but I also don't quite know yet what to do against it at higher speeds.

          I will now jump into the bus and see if I can find a 74LS139.
        • Lee Hart
          ... It worked poorly in the TTL days, as the delays you got were unpredictable and drifted. But it is a reasonable technique with CMOS (as long as you use good
          Message 4 of 30 , Jan 11, 2013
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            joshbensadon wrote:
            > I think bad practice is to use capacitors on digital lines to create
            > extra delays.

            It worked poorly in the TTL days, as the delays you got were
            unpredictable and drifted. But it is a reasonable technique with CMOS
            (as long as you use good stable resistors and capacitors). The input
            impedance of CMOS is so high that it doesn't affect the RC values. The
            input threshold is a percentage of supply voltage, so the delay us
            unaffected by supply voltage. Temperature does not bother it, either.

            > The only area where I would criticize bad practice, would be the
            > crystal oscillator. I've seen a bad design that would only work with
            > chips from one company.

            Ah yes... A classic design mistake is to use a TTL gate as an
            oscillator! It looks easy, but it isn't. Here again, CMOS makes if far
            easier, as they are so much closer to "ideal" logic elements.

            In the olden days, we'd see all sorts of bad practice. Floating inputs,
            TTL oscillators, inadequate bypass capacitors, bad layouts, race
            conditions that depended on propagation delays, etc. Sometimes they were
            just being cheap; other times they just didn't know any better!
            --
            If we knew what we were doing, it wouldn't be called research, would it?
            -- Albert Einstein
            --
            Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
          • Richard
            ... Mission accomplished (on the breadboard). Only three bugs: I used a 74LS192 counter and should have read the datasheet. The 74LS192 is a BCD counter! A
            Message 5 of 30 , Jan 11, 2013
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              > PS. Good for you to build a hex keypad using logic chips!
              >
              > Cheers,
              > Josh
              >

              Mission accomplished (on the breadboard). Only three bugs:

              I used a 74LS192 counter and should have read the datasheet. The 74LS192 is a BCD counter! A 74LS193 would have been correct, but I had none in my parts box, so I ended up with a 74LS163 I found.

              Then I used the wrong output of the comparator, so I should practice counting pins.

              Last, I set the output enable of the (tri-state) latch to 1, which is wrong of course.

              But now it works. The latch holds the values of the last two keys that have been pressed. The parts cost less than 15$ and it needs only four 74LSXXX ICs and it should work with the original Elf, the Elf II and most probably with the Super Elf. I don't know about the Elf 2000 and it definitely is not compatible to the VIP.

              The computers that are not compatible would need some additional logic to use it as an input port or while in load mode.
            • Andrew Wasson
              That s fantastic Richard. I recall trying to come up with a 74xxxx based hex keypad circuit a number of years ago but ran into a problem of data collisions
              Message 6 of 30 , Jan 11, 2013
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                That's fantastic Richard.

                I recall trying to come up with a 74xxxx based hex keypad circuit a number of years ago but ran into a problem of data collisions when moving from the keypad to the latch and didn't take it any further. Good for you! I'll have to pull out a breadboard and see if I can do something similar for my ELF 2K.

                Andrew



                On 2013-01-11, at 4:51 PM, Richard wrote:

                 

                > PS. Good for you to build a hex keypad using logic chips!
                >
                > Cheers,
                > Josh
                >

                Mission accomplished (on the breadboard). Only three bugs:

                I used a 74LS192 counter and should have read the datasheet. The 74LS192 is a BCD counter! A 74LS193 would have been correct, but I had none in my parts box, so I ended up with a 74LS163 I found.

                Then I used the wrong output of the comparator, so I should practice counting pins.

                Last, I set the output enable of the (tri-state) latch to 1, which is wrong of course.

                But now it works. The latch holds the values of the last two keys that have been pressed. The parts cost less than 15$ and it needs only four 74LSXXX ICs and it should work with the original Elf, the Elf II and most probably with the Super Elf. I don't know about the Elf 2000 and it definitely is not compatible to the VIP.

                The computers that are not compatible would need some additional logic to use it as an input port or while in load mode.



              • Richard
                I had to add a fith IC and am going to test it tomorrow. Latching the counter s value at just the right moment worked well, but I overlooked something. The
                Message 7 of 30 , Jan 11, 2013
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                  I had to add a fith IC and am going to test it tomorrow.

                  Latching the counter's value at just the right moment worked well, but I overlooked something. The counter will continue to scan the keyboard and after 16 counts it would latch the same value again.

                  Now, if you remember how the latch stores the upper four bits... Not good, at least if you are unable to press the key for no longer than 16 clock cycles.

                  Now I have added two NAND gates to stop the counter's clock when a value is latched. It should continue again as soon as the key is released.


                  Both the original Elf and the Elf II have two 4016 analog switches. They are decoded to put 8 data bits onto the bus in load mode when input is pressed or at runtime when input port 4 is queried.

                  In the original Elf those 8 bits came directly from the toggle switches, in the Elf II they had a hex keyboard, an encoder and a latch. It turned out that the latch is there to pull off the same trick for the upper bits as I did.

                  Since the Elf 2000 also can have toggle switches or a hex keyboard, I assume that a similar logic for the load mode and input port must exist. In that case you could just connect the output of my latch to that logic and everything should work.

                  I will post the schematic as soon as I have tested stopping the counter as long as a key is pressed. And I wish I had a camera to take a picture of the breadboard and the hand built keyboard. :)

                  And, not to forget, bouncing keys may still be an issue!
                  --- In cosmacelf@yahoogroups.com, Andrew Wasson wrote:
                  >
                  > That's fantastic Richard.
                  >
                  > I recall trying to come up with a 74xxxx based hex keypad circuit a number of years ago but ran into a problem of data collisions when moving from the keypad to the latch and didn't take it any further. Good for you! I'll have to pull out a breadboard and see if I can do something similar for my ELF 2K.
                • David Keith
                  Here is an 16 input to 4 priority encoder circuit that am planing to use to encode my HexKey pad, the EO can be connected to an EF line to sense if a key has
                  Message 8 of 30 , Jan 12, 2013
                  Here is an 16 input to 4 priority encoder circuit that am planing to use to encode my HexKey pad, the EO can be connected to an EF line to sense if a key has been depressed and of course there needs to be a 74HC244 ( 1/2 for 4 bits) buffer onto the 1802 databus..

                  Are images passed through ok??

                  Thanks
                  Dave


                  From: Andrew Wasson <awasson@...>
                  To: cosmacelf@yahoogroups.com
                  Sent: Friday, January 11, 2013 8:38 PM
                  Subject: Re: [cosmacelf] Re: I have just built...



                  That's fantastic Richard.

                  I recall trying to come up with a 74xxxx based hex keypad circuit a number of years ago but ran into a problem of data collisions when moving from the keypad to the latch and didn't take it any further. Good for you! I'll have to pull out a breadboard and see if I can do something similar for my ELF 2K.

                  Andrew



                  On 2013-01-11, at 4:51 PM, Richard wrote:

                   
                  > PS. Good for you to build a hex keypad using logic chips!
                  >
                  > Cheers,
                  > Josh
                  >

                  Mission accomplished (on the breadboard). Only three bugs:

                  I used a 74LS192 counter and should have read the datasheet. The 74LS192 is a BCD counter! A 74LS193 would have been correct, but I had none in my parts box, so I ended up with a 74LS163 I found.

                  Then I used the wrong output of the comparator, so I should practice counting pins.

                  Last, I set the output enable of the (tri-state) latch to 1, which is wrong of course.

                  But now it works. The latch holds the values of the last two keys that have been pressed. The parts cost less than 15$ and it needs only four 74LSXXX ICs and it should work with the original Elf, the Elf II and most probably with the Super Elf. I don't know about the Elf 2000 and it definitely is not compatible to the VIP.

                  The computers that are not compatible would need some additional logic to use it as an input port or while in load mode.







                • Richard
                  And here is the one I just built on the breadboard. The inverter I had to add is annoying. If I were to use this in the Elf, I would certainly look for a spare
                  Message 9 of 30 , Jan 13, 2013
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                    And here is the one I just built on the breadboard. The inverter I had to add is annoying. If I were to use this in the Elf, I would certainly look for a spare inverter / NAND gate / NOR gate on another IC and eliminate it.

                    On the breadboard I used a 555 to generate a 460 Hz clock. That means the keyboard is scanned about 28 times every second. Higher frequencies should not be needed, but are possible. Even the processor's 1.79 MHz clock should work. In fact, I have estimated that even 16 MHz should still be safe, but why should we scan the keyboard a million times every second?

                    And then we still have the question of how to debounce the keyboard. Do we need some kind of RC network on the four row lines coming back from the keyboard? At the moment there are just four pullup resistors, so that the lines don't float when no key is pressed.

                    And now I have to find out how to attach the schematic to this reply....

                    --- In cosmacelf@yahoogroups.com, David Keith wrote:
                    >
                    > Here is an 16 input to 4 priority encoder circuit that am planing to use to encode my HexKey pad, the EO can be connected to an EF line to sense if a key has been depressed and of course there needs to be a 74HC244 ( 1/2 for 4 bits) buffer onto the 1802 databus..
                    >
                    > Are images passed through ok??
                    >
                    > Thanks
                    > Dave
                    >
                    >
                    >
                    > ________________________________
                    > From: Andrew Wasson
                    > To: cosmacelf@yahoogroups.com
                    > Sent: Friday, January 11, 2013 8:38 PM
                    > Subject: Re: [cosmacelf] Re: I have just built...
                  • Richard
                    I m obviously not smart enough to attach the schematic, so I have uploaded it here: http://oi49.tinypic.com/5kkcas.jpg Sorry!
                    Message 10 of 30 , Jan 13, 2013
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                      I'm obviously not smart enough to attach the schematic, so I have uploaded it here:

                      http://oi49.tinypic.com/5kkcas.jpg

                      Sorry!
                    • David Keith
                      Looks like images are not attached to the messages, so I have uploaded the image of 16 input to 4 priority encoder circuit to the groups photo folder:
                      Message 11 of 30 , Jan 13, 2013
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                        Looks like images are not attached to the messages, so I have uploaded the image of "16 input to 4 priority encoder circuit" to the groups photo folder:

                        http://groups.yahoo.com/group/cosmacelf/photos/album/504710089/pic/1672872910/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc

                        I am planning on doing keypad debounce in the hex digit read routine
                        '
                        Thanks
                        Dave


                        From: Richard <r.dienstknecht@...>
                        To: cosmacelf@yahoogroups.com
                        Sent: Sunday, January 13, 2013 9:27 AM
                        Subject: [cosmacelf] Re: I have just built...

                        And here is the one I just built on the breadboard. The inverter I had to add is annoying. If I were to use this in the Elf, I would certainly look for a spare inverter / NAND gate / NOR gate on another IC and eliminate it.

                        On the breadboard I used a 555 to generate a 460 Hz clock. That means the keyboard is scanned about 28 times every second. Higher frequencies should not be needed, but are possible. Even the processor's 1.79 MHz clock should work. In fact, I have estimated that even 16 MHz should still be safe, but why should we scan the keyboard a million times every second?

                        And then we still have the question of how to debounce the keyboard. Do we need some kind of RC network on the four row lines coming back from the keyboard? At the moment there are just four pullup resistors, so that the lines don't float when no key is pressed.

                        And now I have to find out how to attach the schematic to this reply....

                        --- In cosmacelf@yahoogroups.com, David Keith  wrote:
                        >
                        > Here is an 16 input to 4 priority encoder circuit that am planing to use to encode my HexKey pad, the EO can be connected to an EF line to sense if a key has been depressed and of course there needs to be a 74HC244 ( 1/2 for 4 bits) buffer onto the 1802 databus..
                        >
                        > Are images passed through ok??
                        >
                        > Thanks
                        > Dave
                        >
                        >
                        >
                        > ________________________________
                        >  From: Andrew Wasson
                        > To: cosmacelf@yahoogroups.com
                        > Sent: Friday, January 11, 2013 8:38 PM
                        > Subject: Re: [cosmacelf] Re: I have just
                        built...




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                      • Lee Hart
                        ... Looks good, Richard. 5 ICs isn t bad. You can get it down to 4 ICs by replacing IC3 with a 4052. This will eliminate the inverter package. The 4052 is a
                        Message 12 of 30 , Jan 13, 2013
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                          On 1/13/2013 8:31 AM, Richard wrote:
                          > I'm obviously not smart enough to attach the schematic, so I have
                          > uploaded it here: http://oi49.tinypic.com/5kkcas.jpg

                          Looks good, Richard. 5 ICs isn't bad.

                          You can get it down to 4 ICs by replacing IC3 with a 4052. This will
                          eliminate the inverter package. The 4052 is a dual 1-of-4 analog switch.
                          IC1 Qc and Qd go directly to its A and B inputs (IC2b is not needed).
                          One half of the 4053 provides your A=B output to clock IC4. The other
                          half of the 4053 has its common tied *low* to provide the inverted
                          key-down signal to stop the clock (ENP pin of IC1).

                          Debounce: Use a CMOS 74HC374 at IC4. Add an RC delay between IC4 clock
                          and IC3 key-down. When you press a key, the clock is *immediately*
                          stopped, while IC4 will get clocked a millisecond later. If the key
                          bounces, and happens to free the clock to count past that key, it won't
                          get saved in latch IC4.

                          Note that 4 ICs is also enough to do a complete ASCII keyboard! Don
                          Lancaster's "CMOS Cookbook" uses the same idea you did, but with a 4060
                          oscillator-counter for IC1 a 4051 1-of-8 decoder for IC2 and IC3. IC4
                          can be an 8-bit latch with tri-state output to gate the resulting ASCII
                          code onto the bus.
                          --
                          *BE* the change that you wish to see in the world. -- Mahatma Gandhi
                          --
                          Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
                        • Lee Hart
                          ... It came through just fine, David! It s a classic circuit. My Heathkit H8 computer uses exactly this method for its 16-key keypad. -- We live in a Newtonian
                          Message 13 of 30 , Jan 13, 2013
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                            On 1/12/2013 11:12 PM, David Keith wrote:
                            > Here is an 16 input to 4 priority encoder circuit...
                            > Are images passed through ok??

                            It came through just fine, David! It's a classic circuit. My Heathkit H8
                            computer uses exactly this method for its 16-key keypad.

                            --
                            We live in a Newtonian world of Einsteinian physics ruled by
                            Frankenstein logic. -- David Russell
                            --
                            Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
                          • joshbensadon
                            ... Richard, No worries about attachments. You are plenty smart enough to come up with that clever circuit! I see what you mean about the single gate.
                            Message 14 of 30 , Jan 14, 2013
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                              --- In cosmacelf@yahoogroups.com, "Richard" wrote:
                              >
                              > I'm obviously not smart enough to attach the schematic, so I have uploaded it here:
                              >
                              > http://oi49.tinypic.com/5kkcas.jpg
                              >

                              Richard, No worries about attachments. You are plenty smart enough to come up with that clever circuit! I see what you mean about the single gate. Without looking at the logic, etc, I am just wondering if the P<Q could be used in some way to provide the inverted logic to P=Q? Perhaps OR tie P<Q and P>Q with a couple of diodes?

                              But otherwise, very cool circuit, simple and a clever use of all the chips.

                              Cheers,
                              Josh
                            • David Keith
                              Classic :-) well kind of :-)  the 74148 was designed that way to cascade n-bits encoding See Figure 3 on page 13 of 74148 datasheet attached.  :et me know if
                              Message 15 of 30 , Jan 14, 2013
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                              Classic :-) well kind of :-)  the 74148 was designed that way to cascade n-bits encoding

                              See Figure 3 on page 13 of 74148 datasheet attached.  :et me know if you see the attached.

                              Would you have the schematic of the HeathKit H8 you can share? I collect retro-circuits.

                              Thanks
                              Dave



                              From: Lee Hart <leeahart@...>
                              To: cosmacelf@yahoogroups.com
                              Sent: Sunday, January 13, 2013 4:18 PM
                              Subject: Re: [cosmacelf] Re: I have just built...

                              On 1/12/2013 11:12 PM, David Keith wrote:
                              > Here is an 16 input to 4 priority encoder circuit...
                              > Are images passed through ok??

                              It came through just fine, David! It's a classic circuit. My Heathkit H8
                              computer uses exactly this method for its 16-key keypad.

                              --
                              We live in a Newtonian world of Einsteinian physics ruled by
                              Frankenstein logic. -- David Russell
                              --
                              Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm


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                            • Lee Hart
                              ... Yes, I have an H8, and the schematics for it. I don t have a scanner, but it wouldn t surprise me if they are already online somewhere. The H8 has a 16-key
                              Message 16 of 30 , Jan 14, 2013
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                                On 1/14/2013 11:10 AM, David Keith wrote:
                                > Would you have the schematic of the HeathKit H8 you can share? I collect
                                > retro-circuits.

                                Yes, I have an H8, and the schematics for it. I don't have a scanner,
                                but it wouldn't surprise me if they are already online somewhere.

                                The H8 has a 16-key keypad, but uses octal for programming (octal works
                                better for its 8080 CPU than hex). 8 keys were used for the numbers 0-7
                                (placed on the lower 4 bits). The other 8 keys were used for various
                                control functions (read and write to memory and I/O, etc.) and placed on
                                the upper 4 bits. In each 4-bit nibble, 3 bits encode the key, and the
                                4th tells if a key is down. When you pressed a key, it generated an
                                interrupt. Reading the input port got the key pattern, and cleared the
                                intterupt.

                                --
                                The most dangerous enemy of a better solution is an existing one that
                                is just good enough. -- Eric S. Raymond
                                --
                                Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
                              • Richard
                                Sorry for the late reply, but I have started on a new job with two long working days. Tonight I got myself a new little camera and took some pitures of the
                                Message 17 of 30 , Jan 15, 2013
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                                  Sorry for the late reply, but I have started on a new job with two long working days.

                                  Tonight I got myself a new little camera and took some pitures of the keyboard and the breadboard:

                                  http://oi49.tinypic.com/9vefc8.jpg

                                  It still bounces on pressing or releasing a button most of the time, even despite Lee's tips. I have tried capacitors of different values to the point where it did not work at all. There was some small improvement, but it is still far from good.

                                  the circuit on the breadboard also is very noisy. Once the counter stopped counting. It turned out that there was something pulling down VCC, exactly at the frequency of the oscillator. Short,regular signals, going all the way down to 0. I suspect it's the 555 and adding a fat capacitor between VCC and ground helped.

                                  Perhaps I should also add a picture of the old Elf II. At least it also has something uncommon to show: The address and status displays of a Quest Super Elf.

                                  --- In cosmacelf@yahoogroups.com, "joshbensadon" wrote:
                                  >
                                  >
                                  >
                                  > --- In cosmacelf@yahoogroups.com, "Richard" wrote:
                                  > >
                                  > > I'm obviously not smart enough to attach the schematic, so I have uploaded it here:
                                  > >
                                  > > http://oi49.tinypic.com/5kkcas.jpg
                                  > >
                                  >
                                  > Richard, No worries about attachments. You are plenty smart enough to come up with that clever circuit! I see what you mean about the single gate. Without looking at the logic, etc, I am just wondering if the P<q>Q with a couple of diodes?
                                  >
                                  > But otherwise, very cool circuit, simple and a clever use of all the chips.
                                  >
                                  > Cheers,
                                  > Josh
                                  >
                                  </q>
                                • joshbensadon
                                  Hi Richard, Very cool. PS. Why do you have LED s without a series resistor? Where are you putting the capacitor to stop the bouncing? J.
                                  Message 18 of 30 , Jan 15, 2013
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                                    Hi Richard,

                                    Very cool.

                                    PS. Why do you have LED's without a series resistor?

                                    Where are you putting the capacitor to stop the bouncing?

                                    J.



                                    --- In cosmacelf@yahoogroups.com, "Richard" wrote:
                                    >
                                    > Sorry for the late reply, but I have started on a new job with two long working days.
                                    >
                                    > Tonight I got myself a new little camera and took some pitures of the keyboard and the breadboard:
                                    >
                                    > http://oi49.tinypic.com/9vefc8.jpg
                                    >
                                    > It still bounces on pressing or releasing a button most of the time, even despite Lee's tips. I have tried capacitors of different values to the point where it did not work at all. There was some small improvement, but it is still far from good.
                                    >
                                    > the circuit on the breadboard also is very noisy. Once the counter stopped counting. It turned out that there was something pulling down VCC, exactly at the frequency of the oscillator. Short,regular signals, going all the way down to 0. I suspect it's the 555 and adding a fat capacitor between VCC and ground helped.
                                    >
                                    > Perhaps I should also add a picture of the old Elf II. At least it also has something uncommon to show: The address and status displays of a Quest Super Elf.
                                    >
                                    > --- In cosmacelf@yahoogroups.com, "joshbensadon" wrote:
                                    > >
                                    > >
                                    > >
                                    > > --- In cosmacelf@yahoogroups.com, "Richard" wrote:
                                    > > >
                                    > > > I'm obviously not smart enough to attach the schematic, so I have uploaded it here:
                                    > > >
                                    > > > http://oi49.tinypic.com/5kkcas.jpg
                                    > > >
                                    > >
                                    > > Richard, No worries about attachments. You are plenty smart enough to come up with that clever circuit! I see what you mean about the single gate. Without looking at the logic, etc, I am just wondering if the P<q>Q with a couple of diodes?
                                    > >
                                    > > But otherwise, very cool circuit, simple and a clever use of all the chips.
                                    > >
                                    > > Cheers,
                                    > > Josh
                                    > >
                                    > </q>
                                    >
                                  • Lee Hart
                                    ... I don t see any bypass capacitors on the supply. Try adding a 0.1uf to each chip, right at its VCC and GND pins. The 555 timer has very high output drive,
                                    Message 19 of 30 , Jan 15, 2013
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                                      On 1/15/2013 3:29 PM, Richard wrote:
                                      > It still bounces on pressing or releasing a button most of the time,
                                      > even despite Lee's tips. I have tried capacitors of different values
                                      > to the point where it did not work at all. There was some small
                                      > improvement, but it is still far from good.

                                      I don't see any bypass capacitors on the supply. Try adding a 0.1uf to
                                      each chip, right at its VCC and GND pins.

                                      The 555 timer has very high output drive, and spikes the power supply
                                      powerfully. A good bypass capacitor is particularly important on this chip.

                                      --
                                      Anyone can make the simple complicated. Creativity is making the
                                      complicated simple. -- Charles Mingus
                                      --
                                      Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
                                    • Richard
                                      One simple reason: I did not have any at hand. I m going to pick some on my way home from work tomorrow.
                                      Message 20 of 30 , Jan 15, 2013
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                                        One simple reason: I did not have any at hand. I'm going to pick some on my way home from work tomorrow.

                                        --- In cosmacelf@yahoogroups.com, Lee Hart wrote:
                                        >
                                        > On 1/15/2013 3:29 PM, Richard wrote:
                                        > > It still bounces on pressing or releasing a button most of the time,
                                        > > even despite Lee's tips. I have tried capacitors of different values
                                        > > to the point where it did not work at all. There was some small
                                        > > improvement, but it is still far from good.
                                        >
                                        > I don't see any bypass capacitors on the supply. Try adding a 0.1uf to
                                        > each chip, right at its VCC and GND pins.
                                        >
                                        > The 555 timer has very high output drive, and spikes the power supply
                                        > powerfully. A good bypass capacitor is particularly important on this chip.
                                        >
                                        > --
                                        > Anyone can make the simple complicated. Creativity is making the
                                        > complicated simple. -- Charles Mingus
                                        > --
                                        > Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
                                        >
                                      • Richard
                                        At the clock input of the latch. It s the yellow one near the fourth IC and the resistor further to the right. And I plugged in the LEDs when I came back from
                                        Message 21 of 30 , Jan 15, 2013
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                                          At the clock input of the latch. It's the yellow one near the fourth IC and the resistor further to the right.

                                          And I plugged in the LEDs when I came back from work yesterday. It was late already and I guess I was not thinking. For what it's worth, they look far brighter than they really are in the picture and they also don't get warm. Still, it's not so good.

                                          --- In cosmacelf@yahoogroups.com, "joshbensadon" wrote:
                                          >
                                          > Hi Richard,
                                          >
                                          > Very cool.
                                          >
                                          > PS. Why do you have LED's without a series resistor?
                                          >
                                          > Where are you putting the capacitor to stop the bouncing?
                                          >
                                          > J.
                                          >
                                          >
                                          >
                                          > --- In cosmacelf@yahoogroups.com, "Richard" wrote:
                                          > >
                                          > > Sorry for the late reply, but I have started on a new job with two long working days.
                                          > >
                                          > > Tonight I got myself a new little camera and took some pitures of the keyboard and the breadboard:
                                          > >
                                          > > http://oi49.tinypic.com/9vefc8.jpg
                                          > >
                                          > > It still bounces on pressing or releasing a button most of the time, even despite Lee's tips. I have tried capacitors of different values to the point where it did not work at all. There was some small improvement, but it is still far from good.
                                          > >
                                          > > the circuit on the breadboard also is very noisy. Once the counter stopped counting. It turned out that there was something pulling down VCC, exactly at the frequency of the oscillator. Short,regular signals, going all the way down to 0. I suspect it's the 555 and adding a fat capacitor between VCC and ground helped.
                                          > >
                                          > > Perhaps I should also add a picture of the old Elf II. At least it also has something uncommon to show: The address and status displays of a Quest Super Elf.
                                          > >
                                          > > --- In cosmacelf@yahoogroups.com, "joshbensadon" wrote:
                                          > > >
                                          > > >
                                          > > >
                                          > > > --- In cosmacelf@yahoogroups.com, "Richard" wrote:
                                          > > > >
                                          > > > > I'm obviously not smart enough to attach the schematic, so I have uploaded it here:
                                          > > > >
                                          > > > > http://oi49.tinypic.com/5kkcas.jpg
                                          > > > >
                                          > > >
                                          > > > Richard, No worries about attachments. You are plenty smart enough to come up with that clever circuit! I see what you mean about the single gate. Without looking at the logic, etc, I am just wondering if the P<q>Q with a couple of diodes?
                                          > > >
                                          > > > But otherwise, very cool circuit, simple and a clever use of all the chips.
                                          > > >
                                          > > > Cheers,
                                          > > > Josh
                                          > > >
                                          > > </q>
                                          > >
                                          >
                                        • awasson2001
                                          ... Hi Guys, On the topic of DIY keypad circuits, does anyone have a copy of Nov/Dec 1978 Popular Electronics? Popular Electronics was highly influential in
                                          Message 22 of 30 , Apr 24, 2013
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                                            --- In cosmacelf@yahoogroups.com, "Richard" wrote:
                                            >
                                            > I'm obviously not smart enough to attach the schematic, so I have uploaded it here:
                                            >
                                            > http://oi49.tinypic.com/5kkcas.jpg
                                            >
                                            > Sorry!
                                            >

                                            Hi Guys,

                                            On the topic of DIY keypad circuits, does anyone have a copy of Nov/Dec 1978 Popular Electronics?

                                            Popular Electronics was highly influential in motivating me to deposit my meager paper route earnings at the local radio shack which in turn would supply the parts for working thinga-ma-bobs or smoking heaps of melted plastic. It's a real shame Popular Electronics and Radio Electronics are no longer around.

                                            This weekend, I was reviewing hex keypad circuits and I kept thinking back to my first attempt at one... It was before I even had an actual microprocessor to play with but at the time I figured build the input device and the rest would follow. I can still recall the feeling of excitement just of the thought of pushing one of 16 buttons on the keypad that I made and having the appropriate binary representation show up on the 4 single LED display. My attempt sort of worked but it was buggy and at 14-15 years old, I didn't have the know-how to sort it out so the parts were eventually scavenged for other projects, all except for the 74150 16-1 multiplexer chip which is sitting in my parts rack to this day.

                                            On an unrelated search yesterday, I found the first part of the Popular Electronics article with a discussion of the 74150 MUX and part 1 of the keyboard circuit so I thought I'd share it with the group. Hopefully I can find the second part although I have a pretty good idea of what the second part adds to the circuit. I think the core circuit, which is discussed in figure 7 of the Experimenter's Corner part of the PDF is pretty brilliant.

                                            Here it is: http://www.epanorama.net/sff/Digital/Keyboards/The%2074150%20Multiplexer.pdf  

                                            Andrew
                                          • joshbensadon
                                            ... Yes, I have a large collection of PE and RE. It is my pleasure to look through them and scan articles. ... And Radio Shack too. But those were the days
                                            Message 23 of 30 , Apr 24, 2013
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                                              --- In cosmacelf@yahoogroups.com, "awasson2001" <awasson@...> wrote:
                                              >
                                              >
                                              > does anyone have a copy of Nov/Dec 1978 Popular Electronics?
                                              >

                                              Yes, I have a large collection of PE and RE. It is my pleasure to look through them and scan articles.

                                              > It's a real shame Popular Electronics and Radio
                                              > Electronics are no longer around.

                                              And Radio Shack too. But those were the days :) I miss them too.

                                              > so the parts were eventually scavenged for other projects, all except
                                              > for the 74150 16-1 multiplexer chip which is sitting in my parts rack to
                                              > this day.

                                              LoL, yes, I have/had the same life. Parts would get scavenged, projects torn down so new projects could emerge. Flight of the Phoenix?

                                              > Popular Electronics article with a discussion of the 74150 MUX and part 1 of the
                                              > keyboard circuit so I thought I'd share it with the group.
                                              Hopefully I
                                              > can find the second part although I have a pretty good idea of what the
                                              > second part adds to the circuit. I think the core circuit, which is
                                              > discussed in figure 7 of the Experimenter's Corner part of the PDF is
                                              > pretty brilliant.


                                              Yes, I loved those "Experimenter's Corner" and "Beginners Corner" articles. I scanned the 2nd part and the complementary article to the 74150 which is of course the 74154. I will upload it here in the files section and delete it in a few days. Look for PE1978-DEC-pg84 file.

                                              I also scanned many articles for Rich Cini's web site, just search for "Rich Cini Magazines", he's got a lot of good stuff there!

                                              :)J
                                            • Andrew Wasson
                                              Fantastic! Thanks Josh! I ve downloaded the scan from the files section. Now that I see it again, it really seems like yesterday; that s how strong an
                                              Message 24 of 30 , Apr 24, 2013
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                                                Fantastic! Thanks Josh!

                                                I've downloaded the scan from the files section. Now that I see it again, it really seems like yesterday; that's how strong an impression those articles left. Experimenter's corner was the best! I still have a couple of LM3914's that I'm going to make a matchbox oscilloscope with. I think that was from May 1979 but I can't say for sure. 

                                                Also thanks for Rich Cini's magazine archive. That's a goldmine!

                                                Andrew 



                                                On 2013-04-24, at 3:33 PM, joshbensadon wrote:

                                                 

                                                --- In cosmacelf@yahoogroups.com, "awasson2001" <awasson@...> wrote:
                                                >
                                                >
                                                > does anyone have a copy of Nov/Dec 1978 Popular Electronics?
                                                >

                                                Yes, I have a large collection of PE and RE. It is my pleasure to look through them and scan articles.

                                                > It's a real shame Popular Electronics and Radio
                                                > Electronics are no longer around.

                                                And Radio Shack too. But those were the days :) I miss them too.

                                                > so the parts were eventually scavenged for other projects, all except
                                                > for the 74150 16-1 multiplexer chip which is sitting in my parts rack to
                                                > this day.

                                                LoL, yes, I have/had the same life. Parts would get scavenged, projects torn down so new projects could emerge. Flight of the Phoenix?

                                                > Popular Electronics article with a discussion of the 74150 MUX and part 1 of the
                                                > keyboard circuit so I thought I'd share it with the group.
                                                Hopefully I
                                                > can find the second part although I have a pretty good idea of what the
                                                > second part adds to the circuit. I think the core circuit, which is
                                                > discussed in figure 7 of the Experimenter's Corner part of the PDF is
                                                > pretty brilliant.

                                                Yes, I loved those "Experimenter's Corner" and "Beginners Corner" articles. I scanned the 2nd part and the complementary article to the 74150 which is of course the 74154. I will upload it here in the files section and delete it in a few days. Look for PE1978-DEC-pg84 file.

                                                I also scanned many articles for Rich Cini's web site, just search for "Rich Cini Magazines", he's got a lot of good stuff there!

                                                :)J



                                              • joshbensadon
                                                ... You re welcome. Yes, those were very strong impressions left. I wrote a story describing my ELF experience and the best I could do to sum up my feelings
                                                Message 25 of 30 , Apr 24, 2013
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                                                  --- In cosmacelf@yahoogroups.com, Andrew Wasson <awasson@...> wrote:
                                                  >
                                                  > Fantastic! Thanks Josh!
                                                  >
                                                  > I've downloaded the scan from the files section. Now that I see it again, it really seems like yesterday; that's how strong an impression those articles left. Experimenter's corner was the best! I still have a couple of LM3914's that I'm going to make a matchbox oscilloscope with. I think that was from May 1979 but I can't say for sure.
                                                  >
                                                  > Also thanks for Rich Cini's magazine archive. That's a goldmine!
                                                  >
                                                  > Andrew


                                                  You're welcome. Yes, those were very strong impressions left. I wrote a story describing my ELF experience and the best I could do to sum up my feelings as I entered the 7B 30 00 program was say it was a technical "high" feeling. Turning on an LED through software instead of hardware.

                                                  PS. PE1978-Nov also had the TIC-TAC-TOE game for the ELF. I built my light pen using a photo transistor at the end of an old BIC pen and played the game on my original ELF and an old 19" B&W TV that I rescued from the garbage.

                                                  :)J
                                                • David W. Schultz
                                                  ... But did you ever get your B&W TV to display color? Well... faked color. It turns out that if you blink a small block in a large field of white (or was it
                                                  Message 26 of 30 , Apr 24, 2013
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                                                    On 04/24/2013 06:34 PM, joshbensadon wrote:
                                                    > PS. PE1978-Nov also had the TIC-TAC-TOE game for the ELF. I built my
                                                    > light pen using a photo transistor at the end of an old BIC pen and
                                                    > played the game on my original ELF and an old 19" B&W TV that I
                                                    > rescued from the garbage.
                                                    >
                                                    > :)J

                                                    But did you ever get your B&W TV to display color?


                                                    Well... faked color. It turns out that if you blink a small block in a
                                                    large field of white (or was it black?) at just the right rate, you will
                                                    perceive it as having color.

                                                    It wasn't really good for anything but it was interesting.


                                                    --
                                                    David W. Schultz
                                                    http://home.earthlink.net/~david.schultz
                                                    Returned for Regrooving
                                                  • Lee Hart
                                                    ... The Matchbox Oscilloscope! I remember seeing that, and thinking it was an absolutely brilliant hack! It has stuck in my memory to this very day. Some day,
                                                    Message 27 of 30 , Apr 24, 2013
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                                                      Andrew Wasson wrote:
                                                      > Fantastic! Thanks Josh!
                                                      >
                                                      > I've downloaded the scan from the files section. Now that I see it
                                                      > again, it really seems like yesterday; that's how strong an impression
                                                      > those articles left. Experimenter's corner was the best! I still have a
                                                      > couple of LM3914's that I'm going to make a matchbox oscilloscope with.
                                                      > I think that was from May 1979 but I can't say for sure.

                                                      The Matchbox Oscilloscope! I remember seeing that, and thinking it was
                                                      an absolutely brilliant hack! It has stuck in my memory to this very
                                                      day. Some day, I'll have to build one. Forrest Mims is a genius.

                                                      Thanks for bringing back the memories, Josh and Andrew. :-)
                                                      --
                                                      An engineer can do for a nickel what any damn fool can do for a dollar.
                                                      -- Henry Ford
                                                      --
                                                      Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
                                                    • jdrose_8_bit
                                                      ... I remember that as well. I am pretty sure I have the original text packed in a box somewhere. Was able to find the schematic online:
                                                      Message 28 of 30 , Apr 24, 2013
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                                                        --- In cosmacelf@yahoogroups.com, Lee Hart <leeahart@...> wrote:
                                                        >
                                                        > The Matchbox Oscilloscope! I remember seeing that, and thinking it was
                                                        > an absolutely brilliant hack! It has stuck in my memory to this very
                                                        > day. Some day, I'll have to build one. Forrest Mims is a genius.
                                                        >
                                                        > Thanks for bringing back the memories, Josh and Andrew. :-)
                                                        >
                                                        > Lee
                                                        >

                                                        I remember that as well. I am pretty sure I have the original text packed in a box somewhere.

                                                        Was able to find the schematic online:
                                                        http://www.flickr.com/photos/31767011@N02/8679905826/sizes/l/

                                                        Definitely brilliant.
                                                      • Andrew Wasson
                                                        Hi Lee, The pleasure is all mine. Forrest Mims is definitely a genius. I got hooked on his stuff with those big blue Engineers Notebooks you could buy at Radio
                                                        Message 29 of 30 , Apr 24, 2013
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                                                          Hi Lee,

                                                          The pleasure is all mine. Forrest Mims is definitely a genius. I got hooked on his stuff with those big blue Engineers Notebooks you could buy at Radio Shack. I even found some schematics I must have drawn when I was 12 -13 years old for logic driven alarm systems and things like that.

                                                          I'm particularly interested in the Hex keypad circuits because I'll need one for foraging back into our TTL CPU experiments.

                                                          Andrew



                                                          On 2013-04-24, at 6:20 PM, Lee Hart wrote:

                                                          > Andrew Wasson wrote:
                                                          >> Fantastic! Thanks Josh!
                                                          >>
                                                          >> I've downloaded the scan from the files section. Now that I see it
                                                          >> again, it really seems like yesterday; that's how strong an impression
                                                          >> those articles left. Experimenter's corner was the best! I still have a
                                                          >> couple of LM3914's that I'm going to make a matchbox oscilloscope with.
                                                          >> I think that was from May 1979 but I can't say for sure.
                                                          >
                                                          > The Matchbox Oscilloscope! I remember seeing that, and thinking it was
                                                          > an absolutely brilliant hack! It has stuck in my memory to this very
                                                          > day. Some day, I'll have to build one. Forrest Mims is a genius.
                                                          >
                                                          > Thanks for bringing back the memories, Josh and Andrew. :-)
                                                          > --
                                                          > An engineer can do for a nickel what any damn fool can do for a dollar.
                                                          > -- Henry Ford
                                                          > --
                                                          > Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
                                                          >
                                                          >
                                                          > ------------------------------------
                                                          >
                                                          > ========================================================
                                                          > Visit the COSMAC ELF website at http://www.cosmacelf.comYahoo! Groups Links
                                                          >
                                                          >
                                                          >
                                                        • Lee Hart
                                                          ... I think I sent you the schematic for the one I designed for the Membership Card? It was a hex keypad and 2-digit hex LED display, using an EPROM, 74HC393
                                                          Message 30 of 30 , Apr 24, 2013
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                                                            On 4/24/2013 8:58 PM, Andrew Wasson wrote:
                                                            > Hi Lee,
                                                            >
                                                            > The pleasure is all mine. Forrest Mims is definitely a genius. I got hooked on his stuff with those big blue Engineers Notebooks you could buy at Radio Shack. I even found some schematics I must have drawn when I was 12 -13 years old for logic driven alarm systems and things like that.
                                                            >
                                                            > I'm particularly interested in the Hex keypad circuits because I'll need one for foraging back into our TTL CPU experiments.

                                                            I think I sent you the schematic for the one I designed for the
                                                            Membership Card? It was a hex keypad and 2-digit hex LED display, using
                                                            an EPROM, 74HC393 counter, 74LS145 decoder, and 74HC273 octal latch. Of
                                                            course, it stands on the shoulders of giants like Forrest Mims, Don
                                                            Lancaster, and others.

                                                            --
                                                            If we knew what we were doing, it wouldn't be called research, would it?
                                                            -- Albert Einstein
                                                            --
                                                            Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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