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A different kind of SmartSocket - Numitron

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  • urrossum@att.net
    Hello, This is my first post to this group. A while back, I discovered Numitron tubes. They re a seven-segment incandescent display tube that has a simlar
    Message 1 of 5 , Jan 10, 2012
      Hello,

      This is my first post to this group. A while back, I discovered Numitron tubes. They're a seven-segment incandescent display tube that has a simlar retro look to Nixies, but are very easy to drive (they require 3-5 volts at about 20 mA per segment).

      I had plans to use them in everything from clocks to kitchen timers to a thermostat for a wax pot I built, all with a nice retro look. So I designed a board using my favorite little 8051 derivative (AT89C2051) to drive a single digit (the outputs can directly sink 25 mA). The only other components required were a resonator and two small capacitors.

      The idea is that you can daisy-chain as many of the digits together as you want, connecting the serial output of one to the serial input of the next to the left. Then, you just send a data string at 2400 baud (easily bit-banged on any processor) into the rightmost one, and when you send the <CR> at the end of the string, all the digits display the appropriate character. All the numeric digits can be displayed, naturally, and I made a (somewhat weak) attempt to display most of the ASCII letter set as well on the 7 segments.

      The firmware has commands to control the brightness of the display, as well as inverting and powering down. (For decent segment life, and to avoid over-current on the chip outputs, you have to keep the filaments warmed at just below the visible level to prevent the input current surge of a cold filament; the firmware takes care of that too, of course.)

      I had to use the surface mount version of the processor to meet my size target, but it's a fairly forgiving .050 pin spacing (easy to solder by hand), and Jameco was closing out their stock of the chip at less than a buck each, so I bought all they had. I also picked up a couple of hundred Russian IV-9 tubes, again for less than a buck each, and then I use the boards on whichever project is going by at the time. All told, each board costs me about $8 in parts (if I order 100 of the prototype-level bare boards at a time).

      This project took about a day to design the board (then another 4 hours to re-spin it smaller so it would fit in a 24-pin IC socket), plus another 12 hours or so for the firmware - and they work great! Of course, about midway through the project I discovered this group - I guess there's really nothing new under the sun...

      I'll post PDFs of the schematic and board in the files section, along with the source; if anybody wants, I can provide the Gerber files as well.
      --
      Mark Moulding
    • fixitsan2
      ... Hello Mark, I am happy to welcome you to the group and to also thank you for sharing your design with us. You ve caught me at a time when I m also finding
      Message 2 of 5 , Jan 10, 2012
        --- In smartsockets@yahoogroups.com, "urrossum@..." <mark@...> wrote:
        >
        > Hello,
        >
        > This is my first post to this group.
        >
        > This project took about a day to design the board (then another 4 hours to re-spin it smaller so it would fit in a 24-pin IC socket), plus another 12 hours or so for the firmware - and they work great! Of course, about midway through the project I discovered this group - I guess there's really nothing new under the sun...
        >
        > I'll post PDFs of the schematic and board in the files section, along with the source; if anybody wants, I can provide the Gerber files as well.
        > --
        > Mark Moulding
        >

        Hello Mark, I am happy to welcome you to the group and to also thank you for sharing your design with us.

        You've caught me at a time when I'm also finding numitrons quite attractive too.

        Chris
      • michail1@aol.com
        I am interested in seeing it and the prototypes. Pics? Michail 206-920-6312 In a message dated 1/10/2012 12:29:01 A.M. Pacific Standard Time,
        Message 3 of 5 , Jan 10, 2012
          I am interested in seeing it and the prototypes.   Pics?
           
          Michail
          206-920-6312
           
          In a message dated 1/10/2012 12:29:01 A.M. Pacific Standard Time, mark@... writes:
           

          Hello,

          This is my first post to this group. A while back, I discovered Numitron tubes. They're a seven-segment incandescent display tube that has a simlar retro look to Nixies, but are very easy to drive (they require 3-5 volts at about 20 mA per segment).

          I had plans to use them in everything from clocks to kitchen timers to a thermostat for a wax pot I built, all with a nice retro look. So I designed a board using my favorite little 8051 derivative (AT89C2051) to drive a single digit (the outputs can directly sink 25 mA). The only other components required were a resonator and two small capacitors.

          The idea is that you can daisy-chain as many of the digits together as you want, connecting the serial output of one to the serial input of the next to the left. Then, you just send a data string at 2400 baud (easily bit-banged on any processor) into the rightmost one, and when you send the <CR> at the end of the string, all the digits display the appropriate character. All the numeric digits can be displayed, naturally, and I made a (somewhat weak) attempt to display most of the ASCII letter set as well on the 7 segments.

          The firmware has commands to control the brightness of the display, as well as inverting and powering down. (For decent segment life, and to avoid over-current on the chip outputs, you have to keep the filaments warmed at just below the visible level to prevent the input current surge of a cold filament; the firmware takes care of that too, of course.)

          I had to use the surface mount version of the processor to meet my size target, but it's a fairly forgiving .050 pin spacing (easy to solder by hand), and Jameco was closing out their stock of the chip at less than a buck each, so I bought all they had. I also picked up a couple of hundred Russian IV-9 tubes, again for less than a buck each, and then I use the boards on whichever project is going by at the time. All told, each board costs me about $8 in parts (if I order 100 of the prototype-level bare boards at a time).

          This project took about a day to design the board (then another 4 hours to re-spin it smaller so it would fit in a 24-pin IC socket), plus another 12 hours or so for the firmware - and they work great! Of course, about midway through the project I discovered this group - I guess there's really nothing new under the sun...

          I'll post PDFs of the schematic and board in the files section, along with the source; if anybody wants, I can provide the Gerber files as well.
          --
          Mark Moulding

        • urrossum@att.net
          ... I ve finally uploaded some pictures of the Numitron display modules (I certainly wouldn t deign to assume the SmartSocket term for them!). Since my last
          Message 4 of 5 , Mar 5, 2012
            > I am interested in seeing it and the prototypes. Pics?

            I've finally uploaded some pictures of the Numitron display modules (I certainly wouldn't deign to assume the SmartSocket term for them!). Since my last post, I've re-spun the project slightly. Each digit now has a programmable-brightness uplight, and I've gone to all surface mount components (only 6 total, including the processor and LED) for a lower profile. Also, it now fits exactly into a 24-pin DIP socket.

            Three of the pictures show the newer model module, with the uplight at half-brightness. The Numitron is also only at 60% brightness; I find this is adequate for most lighting situations, and extends the life nearly indefinitely. (US-made Numitrons are typically rated at 50,000 hours life at full operating voltage - I assume that the Russian ones I used are similar.)

            Other pictures show three of the older-style modules (without the uplight) grouped together, ready for installation into a project (an indoor/outdoor thermometer for the bedroom, this time). Also shown is a temperature-controlled wax pot I built using an identical chain of modules.

            Note that only 5 volts, ground, and a single 2400-baud TTL-level communication line is necessary to operate any number of modules. I've been making some high-brightness daylight readable large (6") 7-segment displays for sports scoreboards lately, and I used the same protocol there; it really simplified the programming of the main processor. In fact, those displays can exist in the same chain as the Numitron devices (though I can't image what context I'd mix these technologies in...).
            --
            Mark Moulding
          • urrossum@att.net
            PS - the pictures are in the Numitron SmartSocket folder of the Files area, *not* in the Photos area. -- Mark Moulding
            Message 5 of 5 , Mar 5, 2012
              PS - the pictures are in the "Numitron SmartSocket" folder of the Files area, *not* in the Photos area.
              --
              Mark Moulding
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