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Solarbotics Servocore (was 74**240)

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  • J Wolfgang Goerlich
    ... Is this a required or a recommended practice? The Solarbotics BEP Servocore project does not include a regulator. Perhaps Beam circuit designs can work
    Message 1 of 14 , Dec 1, 2003
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      Eric Seale wrote:
      > the HCT requires 5 V regulated power. If you don't want to
      > stick a regulator on your critters, stick to the HC.

      Is this a required or a recommended practice? The Solarbotics BEP
      Servocore project does not include a regulator. Perhaps Beam circuit
      designs can work without one? Or, perhaps that is why my Servocore is
      not yet walking?

      J Wolfgang Goerlich
    • Wilf Rigter
      With regulated Vcc, Bicore timing will vary less. Since the hobby servos use precise timing pulses for positioning, changes in Vcc can cause an offset in the
      Message 2 of 14 , Dec 1, 2003
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        With regulated Vcc, Bicore timing will vary less. Since the hobby servos use
        precise timing pulses for positioning, changes in Vcc can cause an offset in
        the leg orientation.

        wilf



        ----- Original Message -----
        From: "J Wolfgang Goerlich" <jwgoerlich@...>
        To: <beam@yahoogroups.com>
        Sent: Monday, December 01, 2003 12:33 AM
        Subject: [beam] Solarbotics Servocore (was 74**240)


        > Eric Seale wrote:
        > > the HCT requires 5 V regulated power. If you don't want to
        > > stick a regulator on your critters, stick to the HC.
        >
        > Is this a required or a recommended practice? The Solarbotics BEP
        > Servocore project does not include a regulator. Perhaps Beam circuit
        > designs can work without one? Or, perhaps that is why my Servocore is
        > not yet walking?
        >
        > J Wolfgang Goerlich
        >
        >
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      • Adi Shavit
        Hi, Here are some other factoids: with the same R/C components, a 74HCT240 bicore oscillates faster and is more noise resistant than a 74HC240 bicore but a
        Message 3 of 14 , Dec 1, 2003
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          Hi,
           
          Here are some other factoids:  with the same R/C components, a 74HCT240
          bicore oscillates faster and is more "noise" resistant than a 74HC240 bicore
          but a 74HCT14 microcore oscillates slower than a 74HC14 microcore.  Can you
          see why?
          OK, I'll bite. I think I understand the first part.
          According to this the 74HCT240 has a ""fixed" input switching point of about 1.6V", as opposed to the 74HC240 which has "input voltage trigger / switching level about 1/2 of Vcc", so, if normally Vcc is larger than 3.2V, say 5V, a (suspended-)bicore will oscillate faster since the caps will charge over the trigger threshold of 1.6V easier, the bigger Vcc is.
           
          If my suspended bicore description message was correct, then since each cap will asymptotically charge to Vcc/2, one of them will have no trouble passing 1.6V (when Vcc>3.2V), and thus triggering the next oscillation sooner.
          This, will also explain the robustness to noise, since the voltage across the resistor will be farther from 0 when the switching occurs, so the noise must be bigger to interfere.
           
          I now think I can also venture a guess as to the second part.
          Again, assuming Vcc > 3.2, say 5V, since the microcore is active low (I think that's the right term), it means that given an input high pulse, the inverter will invert it to a low (the active output), an will stay there until the Nv cap charges to the switching threshold.
          But since the cap is charging "negatively" (active high) it has to charge, in the HC case, to Vcc-Vcc/2=Vcc/2=2.5V for the inverter to switch (remember we are talking about 74**240, so this is NOT a Schmidt inverter).
          However in the HCT case, the switching threshold is a "fixed" 1.6V, so the cap will have to charge Vcc-1.6V=5-1.6=3.4V before the inverter triggers, thus, this takes a longer time and explains the slower oscillations of the 74HCT240 microcore.
           
          I found this little animation very helpful in understanding the cap and microcore behavior:
           
           
          you can also see it here if this link/animation fails.
           
          Please comment,
          Adi
           
           
           
           
        • Adi Shavit
          Hi Wilf, I was wondering if my understanding was correct. Thanks, Adi ... From: Adi Shavit To: beam@yahoogroups.com Sent: Tuesday, December 02, 2003 1:42 AM
          Message 4 of 14 , Dec 4, 2003
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            Hi Wilf,
             
              I was wondering if my understanding was correct.
             
            Thanks,
            Adi
            ----- Original Message -----
            Sent: Tuesday, December 02, 2003 1:42 AM
            Subject: Re: [beam] Re: 74**240

            Hi,
             
            Here are some other factoids:  with the same R/C components, a 74HCT240
            bicore oscillates faster and is more "noise" resistant than a 74HC240 bicore
            but a 74HCT14 microcore oscillates slower than a 74HC14 microcore.  Can you
            see why?
            OK, I'll bite. I think I understand the first part.
            According to this the 74HCT240 has a ""fixed" input switching point of about 1.6V", as opposed to the 74HC240 which has "input voltage trigger / switching level about 1/2 of Vcc", so, if normally Vcc is larger than 3.2V, say 5V, a (suspended-)bicore will oscillate faster since the caps will charge over the trigger threshold of 1.6V easier, the bigger Vcc is.
             
            If my suspended bicore description message was correct, then since each cap will asymptotically charge to Vcc/2, one of them will have no trouble passing 1.6V (when Vcc>3.2V), and thus triggering the next oscillation sooner.
            This, will also explain the robustness to noise, since the voltage across the resistor will be farther from 0 when the switching occurs, so the noise must be bigger to interfere.
             
            I now think I can also venture a guess as to the second part.
            Again, assuming Vcc > 3.2, say 5V, since the microcore is active low (I think that's the right term), it means that given an input high pulse, the inverter will invert it to a low (the active output), an will stay there until the Nv cap charges to the switching threshold.
            But since the cap is charging "negatively" (active high) it has to charge, in the HC case, to Vcc-Vcc/2=Vcc/2=2.5V for the inverter to switch (remember we are talking about 74**240, so this is NOT a Schmidt inverter).
            However in the HCT case, the switching threshold is a "fixed" 1.6V, so the cap will have to charge Vcc-1.6V=5-1.6=3.4V before the inverter triggers, thus, this takes a longer time and explains the slower oscillations of the 74HCT240 microcore.
             
            I found this little animation very helpful in understanding the cap and microcore behavior:
             
             
            you can also see it here if this link/animation fails.
             
            Please comment,
            Adi
             
          • Wilf Rigter
            Sorry Adi, It s near year end and I m a bit busy. You have it essentially correct and ... charge, in the HC case, ... talking about 74**240, ... The logic is
            Message 5 of 14 , Dec 4, 2003
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              Sorry Adi,

              It's near year end and I'm a bit busy. You have it essentially correct and
              there is just a small error in the details:

              > But since the cap is charging "negatively" (active high) it has to
              charge, in the HC case,
              > to Vcc-Vcc/2=Vcc/2=2.5V for the inverter to switch (remember we are
              talking about 74**240,
              > so this is NOT a Schmidt inverter).

              The logic is right however a microcore only works with Schmitt trigger
              inverters. With Vcc=5V, the lower threshold is about 2V for a 74HC14 and 1V
              for a 74HCT14 inverter.

              > However in the HCT case, the switching threshold is a "fixed" 1.6V, so
              the cap will have to charge
              > Vcc-1.6V=5-1.6=3.4V before the inverter triggers, thus, this takes a
              longer time and explains
              > the slower oscillations of the 74HCT240 microcore

              Check the manufacturer's data sheet for 74HC14 thresholds since they vary
              significantly from one make to the other. Interestingly, if you connect the
              microcore resistors to Vcc common (ie active high outputs) the HC14 version
              oscilates faster than the HCT version.

              regards

              wilf



              ----- Original Message -----
              From: "Adi Shavit" <adish@...>
              To: <beam@yahoogroups.com>
              Sent: Thursday, December 04, 2003 3:33 PM
              Subject: Re: [beam] Re: 74**240


              Hi Wilf,

              I was wondering if my understanding was correct.

              Thanks,
              Adi
              ----- Original Message -----
              From: Adi Shavit
              To: beam@yahoogroups.com
              Sent: Tuesday, December 02, 2003 1:42 AM
              Subject: Re: [beam] Re: 74**240


              Hi,

              Here are some other factoids: with the same R/C components, a 74HCT240
              bicore oscillates faster and is more "noise" resistant than a 74HC240
              bicore
              but a 74HCT14 microcore oscillates slower than a 74HC14 microcore. Can
              you
              see why?
              OK, I'll bite. I think I understand the first part.
              According to this the 74HCT240 has a ""fixed" input switching point of
              about 1.6V", as opposed to the 74HC240 which has "input voltage trigger /
              switching level about 1/2 of Vcc", so, if normally Vcc is larger than 3.2V,
              say 5V, a (suspended-)bicore will oscillate faster since the caps will
              charge over the trigger threshold of 1.6V easier, the bigger Vcc is.

              If my suspended bicore description message was correct, then since each
              cap will asymptotically charge to Vcc/2, one of them will have no trouble
              passing 1.6V (when Vcc>3.2V), and thus triggering the next oscillation
              sooner.
              This, will also explain the robustness to noise, since the voltage across
              the resistor will be farther from 0 when the switching occurs, so the noise
              must be bigger to interfere.

              I now think I can also venture a guess as to the second part.
              Again, assuming Vcc > 3.2, say 5V, since the microcore is active low (I
              think that's the right term), it means that given an input high pulse, the
              inverter will invert it to a low (the active output), an will stay there
              until the Nv cap charges to the switching threshold.
              But since the cap is charging "negatively" (active high) it has to charge,
              in the HC case, to Vcc-Vcc/2=Vcc/2=2.5V for the inverter to switch (remember
              we are talking about 74**240, so this is NOT a Schmidt inverter).
              However in the HCT case, the switching threshold is a "fixed" 1.6V, so the
              cap will have to charge Vcc-1.6V=5-1.6=3.4V before the inverter triggers,
              thus, this takes a longer time and explains the slower oscillations of the
              74HCT240 microcore.

              I found this little animation very helpful in understanding the cap and
              microcore behavior:



              you can also see it here if this link/animation fails.

              Please comment,
              Adi
            • Adi Shavit
              Hi, Thanks, I see what you mean. The active high microcore also makes sense due to the same logic. Thanks a lot, Adi ... From: Wilf Rigter To:
              Message 6 of 14 , Dec 5, 2003
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                Hi,
                 
                 Thanks, I see what you mean.
                The "active high" microcore also makes sense due to the same logic.
                 
                Thanks a lot,
                Adi
                ----- Original Message -----
                Sent: Friday, December 05, 2003 8:08 AM
                Subject: Re: [beam] Re: 74**240

                Sorry Adi,

                It's near year end and I'm a bit busy.  You have it essentially correct and
                there is just a small error in the details:

                >  But since the cap is charging "negatively" (active high) it has to
                charge, in the HC case,
                >  to Vcc-Vcc/2=Vcc/2=2.5V for the inverter to switch (remember we are
                talking about 74**240,
                >  so this is NOT a Schmidt inverter).

                The logic is right however a microcore only works with Schmitt trigger
                inverters. With Vcc=5V, the lower threshold is about 2V for a 74HC14 and 1V
                for a 74HCT14  inverter.

                >  However in the HCT case, the switching threshold is a "fixed" 1.6V, so
                the cap will have to charge
                >  Vcc-1.6V=5-1.6=3.4V before the inverter triggers, thus, this takes a
                longer time and explains
                >  the slower oscillations of the 74HCT240 microcore

                Check the manufacturer's data sheet for 74HC14 thresholds since they vary
                significantly from one make to the other. Interestingly, if you connect the
                microcore resistors to Vcc common (ie active high outputs) the HC14 version
                oscilates faster than the HCT version.

                regards

                wilf



                ----- Original Message -----
                From: "Adi Shavit" <adish@...>
                To: <beam@yahoogroups.com>
                Sent: Thursday, December 04, 2003 3:33 PM
                Subject: Re: [beam] Re: 74**240


                Hi Wilf,

                  I was wondering if my understanding was correct.

                Thanks,
                Adi
                  ----- Original Message -----
                  From: Adi Shavit
                  To: beam@yahoogroups.com
                  Sent: Tuesday, December 02, 2003 1:42 AM
                  Subject: Re: [beam] Re: 74**240


                  Hi,

                    Here are some other factoids:  with the same R/C components, a 74HCT240
                    bicore oscillates faster and is more "noise" resistant than a 74HC240
                bicore
                    but a 74HCT14 microcore oscillates slower than a 74HC14 microcore.  Can
                you
                    see why?
                  OK, I'll bite. I think I understand the first part.
                  According to this the 74HCT240 has a ""fixed" input switching point of
                about 1.6V", as opposed to the 74HC240 which has "input voltage trigger /
                switching level about 1/2 of Vcc", so, if normally Vcc is larger than 3.2V,
                say 5V, a (suspended-)bicore will oscillate faster since the caps will
                charge over the trigger threshold of 1.6V easier, the bigger Vcc is.

                  If my suspended bicore description message was correct, then since each
                cap will asymptotically charge to Vcc/2, one of them will have no trouble
                passing 1.6V (when Vcc>3.2V), and thus triggering the next oscillation
                sooner.
                  This, will also explain the robustness to noise, since the voltage across
                the resistor will be farther from 0 when the switching occurs, so the noise
                must be bigger to interfere.

                  I now think I can also venture a guess as to the second part.
                  Again, assuming Vcc > 3.2, say 5V, since the microcore is active low (I
                think that's the right term), it means that given an input high pulse, the
                inverter will invert it to a low (the active output), an will stay there
                until the Nv cap charges to the switching threshold.
                  But since the cap is charging "negatively" (active high) it has to charge,
                in the HC case, to Vcc-Vcc/2=Vcc/2=2.5V for the inverter to switch (remember
                we are talking about 74**240, so this is NOT a Schmidt inverter).
                  However in the HCT case, the switching threshold is a "fixed" 1.6V, so the
                cap will have to charge Vcc-1.6V=5-1.6=3.4V before the inverter triggers,
                thus, this takes a longer time and explains the slower oscillations of the
                74HCT240 microcore.

                  I found this little animation very helpful in understanding the cap and
                microcore behavior:



                  you can also see it here if this link/animation fails.

                  Please comment,
                  Adi


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