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Re: IV-17 / IV-4 Smartsockets. Group input requested !

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  • Chris
    ... Just to let yoiu know that I ve already changed the spec. Now, I am looking at making a 4 tube board, where each tube is individually programmable with
    Message 1 of 18 , Jun 11, 2009
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      --- In smartsockets@yahoogroups.com, "tkennedyny" <terry+yg@...> wrote:
      >
      > --- In smartsockets@yahoogroups.com, "Chris" <fixitsan@> wrote:
      > >Does anyone feel there is something which is missing from the original device, or if there is a modification you would like to add to a 'wish list' so that I can try to incorporate it in this version (and possibly update the B7971 and ZM1350 versions too , eventually)
      >
      > Can the brightness be controlled by the firmware? Assuming the filament and anode voltages are fixed, I guess this would have to be done by turning each segment off and on with a varying duty cycle.
      >


      Just to let yoiu know that I've already changed the spec.
      Now, I am looking at making a 4 tube board, where each tube is individually programmable with effects and fonts. The groups of 4 could be daisychained together to make a tube array with a maximum size of 252 tubes.

      I have had to move up to a larger and more expenisve processor in order to do this, but overall the cost ratio of discrete components to tubes is better than for a basic 2 tube board. This larger processor could mean that I am also able to incorporate the anode power supply into the design which would keep the cost down to a minimum. I am investigating the options for a 2.2V to 2.4V AC supply driven from the same processor to power the tube filaments too.

      There is more than enough spare memeory to also include something like a GKK or FLW emulator too, but one step at a time for now.

      I have built the first 4 tube array controlled by a single processor and am ironing out a couple of glitches before I implement all of the transition effects, but it does appear that even though the display is multiplexed the fade effects are still very smooth.

      For now, I hope nobody holds their breath for this to be developed, it is very much a 'back of the bench' project, but it is something I sincerely hope to complete due to the obvious technical challenges involved !

      Chris
    • guus.assmann@wolmail.nl
      If you like, I could design a PCB and build a prototype. BR/ Guus Assmann
      Message 2 of 18 , Jun 12, 2009
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        If you like, I could design a PCB and build a prototype.

        BR/
        Guus Assmann

        >-- Oorspronkelijk bericht --
        >To: smartsockets@yahoogroups.com
        >From: "Chris" <fixitsan@...>
        >Date: Thu, 11 Jun 2009 21:21:14 -0000
        >Subject: [smartsockets] Re: IV-17 / IV-4 Smartsockets. Group input requested
        >!
        >Reply-To: smartsockets@yahoogroups.com
        >
        >
        >
        >Just to let yoiu know that I've already changed the spec.
        >Now, I am looking at making a 4 tube board, where each tube is individually
        >programmable with effects and fonts. The groups of 4 could be daisychained
        >together to make a tube array with a maximum size of 252 tubes.

        >>
        >For now, I hope nobody holds their breath for this to be developed, it is
        >very much a 'back of the bench' project, but it is something I sincerely
        >hope to complete due to the obvious technical challenges involved !
        >
        >Chris
        >
      • Chris
        ... Thanks for the offer guus. I really would rather have a go myself because it seems I would like to get my first surface mount PCB under my belt. At the
        Message 3 of 18 , Jun 12, 2009
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          --- In smartsockets@yahoogroups.com, guus.assmann@... wrote:
          >
          > If you like, I could design a PCB and build a prototype.
          >
          > BR/
          > Guus Assmann

          Thanks for the offer guus. I really would rather have a go myself because it seems I would like to get my first surface mount PCB under my belt.

          At the moment I am using a 40pin DIP packaged 18F4620, but this device is also available in 44-pin TQFP and a 44-pin QFN package. I'll also be using either 3 of ULN 2003 plus 1 npn transistor (50V, 10mA), or, 22 discrete transistors, and no ULN2003's. Each segment (18 of them) requires a pullup resistor (1/8w maximum) and the 4 grids also have pullups of 1/4W rating.

          I suppose a schematic speaks a thousand words, so I'll see what I can come up with, but the actual pinout connections between the PIC and the segment drivers is pretty arbitrary and can easily be changed to suit the layout.

          The tricky thing is going to be putting down the traces to multiplex four 18-segment tubes in parallel, and still have enough routing space to make the intermediate driver connections.

          This afternoon I've got all 4 tubes multiplexing succesfully (two IV-17 and two IV-4 together for comparison), and the voltage needed to come up to 40V to get the best looking display. I have got a nice smooth fading effect which operates independnetly of any other effect taking place on any other tube. Getting all tubes to behave as if they had their own smartsocket driver has been the hardest part, and now it's just a case of adding effects and transitions, and of course, having 64k of memory means there is room for lots of fonts too !

          I'll keep your kind offer in mind, and I'll put up a preliminary schematic as soon as I am comfortable with the design.

          Chris
        • Jared Hess
          ... How long do you think it will be until the boards are available? Not to be impatient or anything, just curious.
          Message 4 of 18 , Jun 21, 2009
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            --- In smartsockets@yahoogroups.com, "Chris" <fixitsan@...> wrote:
            >
            > --- In smartsockets@yahoogroups.com, "tkennedyny" <terry+yg@> wrote:
            > >
            > > --- In smartsockets@yahoogroups.com, "Chris" <fixitsan@> wrote:
            > > >Does anyone feel there is something which is missing from the original device, or if there is a modification you would like to add to a 'wish list' so that I can try to incorporate it in this version (and possibly update the B7971 and ZM1350 versions too , eventually)
            > >
            > > Can the brightness be controlled by the firmware? Assuming the filament and anode voltages are fixed, I guess this would have to be done by turning each segment off and on with a varying duty cycle.
            > >
            >
            >
            > Just to let yoiu know that I've already changed the spec.
            > Now, I am looking at making a 4 tube board, where each tube is individually programmable with effects and fonts. The groups of 4 could be daisychained together to make a tube array with a maximum size of 252 tubes.
            >
            > I have had to move up to a larger and more expenisve processor in order to do this, but overall the cost ratio of discrete components to tubes is better than for a basic 2 tube board. This larger processor could mean that I am also able to incorporate the anode power supply into the design which would keep the cost down to a minimum. I am investigating the options for a 2.2V to 2.4V AC supply driven from the same processor to power the tube filaments too.
            >
            > There is more than enough spare memeory to also include something like a GKK or FLW emulator too, but one step at a time for now.
            >
            > I have built the first 4 tube array controlled by a single processor and am ironing out a couple of glitches before I implement all of the transition effects, but it does appear that even though the display is multiplexed the fade effects are still very smooth.
            >
            > For now, I hope nobody holds their breath for this to be developed, it is very much a 'back of the bench' project, but it is something I sincerely hope to complete due to the obvious technical challenges involved !
            >
            > Chris
            >



            How long do you think it will be until the boards are available? Not to be impatient or anything, just curious.
          • Chris
            ... I m sorry that I can t be more precise, but between a few weeks and a few months. I am in the process of changing the hardware again now, and instead of
            Message 5 of 18 , Jun 22, 2009
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              --- In smartsockets@yahoogroups.com, "Jared Hess" <nobody6.1@...>

              >
              > How long do you think it will be until the boards are available? Not to be impatient or anything, just curious.
              >

              I'm sorry that I can't be more precise, but between a few weeks and a few months.
              I am in the process of changing the hardware again now, and instead of controlling each segment by shorting it to ground I am trying to make use of a Supertex HV driver.

              My previous attempts with this device were not good enough, probably because I hadn't figured out how to operate independent effects for each tube while at the same time all tubes were multiplexed from a single driver. There's a lot of jumping about with timings

              I think I should be able to remedy the problems and be more successful this time. I want to put everything onto a single board, driven by a single 12V (or possibly 5V) supply. Vbb needs to be about 40V, and I'm working on a way to put this supply onboard, controlled by the main controller.

              I have no idea about cost just yet, but I will probably be attempting to sell these for profit this time, due to me having collected over £16k in student loan from the government which I will have to start paying back soon !

              Chris
            • taylorjpt
              ... Is the Vbb a fixed 40V or adjustable (You re doing brightness in software, right)? A saturating converter is an easy way to get the voltage you need plus
              Message 6 of 18 , Jun 22, 2009
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                > I think I should be able to remedy the problems and be more successful this time. I want to put everything onto a single board, driven by a single 12V (or possibly 5V) supply. Vbb needs to be about 40V, and I'm working on a way to put this supply onboard, controlled by the main controller.

                Is the Vbb a fixed 40V or adjustable (You're doing brightness in software, right)? A saturating converter is an easy way to get the voltage you need plus an AC filament voltage.

                jt
              • Chris
                ... It is not fixed John. I am using 40V as a ballpark figure. Adjusting brightness by adjusting voltage is known to cause problems with nixies,and I have also
                Message 7 of 18 , Jun 22, 2009
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                  --- In smartsockets@yahoogroups.com, "taylorjpt" <jpt@...> wrote:
                  >
                  > > I think I should be able to remedy the problems and be more successful this time. I want to put everything onto a single board, driven by a single 12V (or possibly 5V) supply. Vbb needs to be about 40V, and I'm working on a way to put this supply onboard, controlled by the main controller.
                  >
                  > Is the Vbb a fixed 40V or adjustable (You're doing brightness in software, right)? A saturating converter is an easy way to get the voltage you need plus an AC filament voltage.
                  >
                  > jt
                  >

                  It is not fixed John. I am using 40V as a ballpark figure.

                  Adjusting brightness by adjusting voltage is known to cause problems with nixies,and I have also read about some problems with VFDs being underdriven. I'll be adjusting brightness through PWM of duty cycle of individual segments.

                  I've spent a few hours so far today on the Supertex driver with and four tubes in parallel/multiplexed idea. I am pleased with how it is working out. If the worst comes to the worst i will not include brightness control except for the cross fading effects, but I'm already multiplexing so duty cycle pwm is already almost built in.

                  I have used a PWM signal to generate 200V for nixies, so I guess it won't be too difficult to get a lower voltage. At 45V the current is typically 25mA.

                  The filament voltage isn't causing me problems, I just need to narrow my options. AC seems to only be used to prevent a voltage gradient from causing uneven tube wear. On a large display with long filaments there could also be a visible difference in brightness. But, the AC frequency is unimportant, and if it is easier just to switch the filament polarity once per minute or once per second then I may just do that, because there is no noticeable brightness gradient with these tubes, which I think is related to the folded shape of the filament, which is 'n' shaped.

                  Of course, if it is trivial to take a tap off the Vbb supply to derive a filament AC voltage then I should look into that idea.What did you have in mind ?



                  Chris
                • taylorjpt
                  ... http://www.tayloredge.com/reference/Electronics/Displays/VFD.pdf http://www.tayloredge.com/reference/Electronics/Displays/Neon_NegativeResistance.GIF The
                  Message 8 of 18 , Jun 22, 2009
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                    > Adjusting brightness by adjusting voltage is known to cause problems with nixies,and I have also read about some problems with VFDs being underdriven. I'll be adjusting brightness through PWM of duty cycle of individual segments.

                    > The filament voltage isn't causing me problems, I just need to narrow my options. AC seems to only be used to prevent a voltage gradient from causing uneven tube wear. On a large display with long filaments there could also be a visible difference in brightness. But, the AC frequency is unimportant, and if it is easier just to switch the filament polarity once per minute or once per second then I may just do that, because there is no noticeable brightness gradient with these tubes, which I think is related to the folded shape of the filament, which is 'n' shaped.


                    http://www.tayloredge.com/reference/Electronics/Displays/VFD.pdf
                    http://www.tayloredge.com/reference/Electronics/Displays/Neon_NegativeResistance.GIF

                    The VFD does not have the negative resistance characteristic of the gas discharge tube; brightness for the VFD is still a function of current but more so because of the speed of the electrons rather than the number. The faster the electrons go, the more that get through the grid which is usually at the same voltage as the anode. This is why the current for a display with all segments on is essentially the same as when they are all off with the delta being higher as the cathode to anode voltage is increased. In general, most of the electrons make the loop through the grid which is why a gridless tube is more efficient than a multiplexed tube for the same light output.

                    One of the problems when using a DC filament drive has to do with the fact that to fully turn off a grid you usually have to switch it to a voltage somewhat less than the filament to create an opposing electrostatic field else some electrons will leak through to the high voltage anodes. With one end of the filament at ground, this would indicate a negative voltage for off grids. You can bias the (-) end of the filament above ground, but this only worsens any kind of unevenness across the character and eats some power.

                    ...but I run on!

                    jt
                  • Chris
                    ... So, according to that datasheet, controlling brightness by controlling voltage is definitely a bad idea. SO I m on the right track by sticking with duty
                    Message 9 of 18 , Jun 22, 2009
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                      --- In smartsockets@yahoogroups.com, "taylorjpt" <jpt@...> wrote:
                      >

                      > http://www.tayloredge.com/reference/Electronics/Displays/VFD.pdf

                      So, according to that datasheet, controlling brightness by controlling voltage is definitely a bad idea. SO I'm on the right track by sticking with duty cycle PWM.

                      I understand the possibility of those problems described in the datasheet when running the filament from a DC supply, but I'm satisfied that there is no visible leakage. Presumably the tubes become less sensitive with age, and darken accordingly, which would seem to suggest that if there is no ghosting or visible leakage now then there is unlikely to be any in the future ?

                      John, what was your idea regarding the power supply ? I want to keep the amount of magnetics down to a minimum. I've even considered specifying an 12V AC supply, which would make a lot of sense if AC is required.

                      I seem to be on the right track at the moment but I know what sort of problems to watch out for now !

                      Chris
                    • John Rehwinkel
                      ... I m probably not the John you meant, but I like to capacitively couple a square wave to the filament. You can adjust the current via capacitor size and
                      Message 10 of 18 , Jun 22, 2009
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                        > John, what was your idea regarding the power supply ? I want to keep
                        > the amount of magnetics down to a minimum. I've even considered
                        > specifying an 12V AC supply, which would make a lot of sense if AC
                        > is required.

                        I'm probably not the John you meant, but I like to capacitively couple
                        a square wave to the filament. You can adjust the current via
                        capacitor size and square wave frequency, or use a series resistor.
                        Try to have your filament drive frequency not be a multiple of your
                        mux frequency.

                        – John
                      • Chris
                        ... Good tips, thanks. I ll be looking to run the SMPS at above 20kHz, so what would be the best way to couple the filament drive to the square wave signal if
                        Message 11 of 18 , Jun 22, 2009
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                          --- In smartsockets@yahoogroups.com, John Rehwinkel <jrehwin@...> wrote:
                          >

                          > I'm probably not the John you meant, but I like to capacitively couple
                          > a square wave to the filament. You can adjust the current via
                          > capacitor size and square wave frequency, or use a series resistor.
                          > Try to have your filament drive frequency not be a multiple of your
                          > mux frequency.
                          >
                          > – John
                          >

                          Good tips, thanks.

                          I'll be looking to run the SMPS at above 20kHz, so what would be the best way to couple the filament drive to the square wave signal if the output signal from the onboard PWM module switches 5V at about 20mA ?

                          So far I have a 40 pin pic with 64k memory driving a Supertex HV5812 which connects to 4 multiplexed tubes, two of which are IV-4 and two are IV-17 (for comparison). The pic will eventually be changed for another one with the least required memory,to keep costs down. Vbb is 40V at 25mA. It might be possible to get the size down to as little as 90mm long and 25mm wide for a 4 tube array

                          I've just finished tweaking one 'segment dance' transition effect and confirmed that one tube can run one effect while it's neighbour can be running another type of effect (such as crossfading) starting at a completely different time. Each tube acts completely independently of it's neighbours, which was the hardest part of coding to get right

                          Now its just a case of writing the dozen or so fonts, and about as many transition effects too. (There's still room for lots more too)

                          I'll look at the power supply in due course, and will probably implement either P+I or FL control of the output (assuming 'differential gap' isn't good enough). The only problem with coupling the filament supply to the Vbb supply is that if the Vbb is required to change duty cycle then _both_ output voltages will change. But thinking about it some more there is most likely plenty of tolerance around the filament voltage so maybe that won't be too much of an issue ? I'll have to test it for myself.


                          Chris

                          Chris
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