problems driving IN-4 Nixie with MPSA42 transistors

Discussion in 'The Projects Forum' started by Bp_968, Apr 15, 2014.

  1. Bp_968

    Thread Starter New Member

    Dec 25, 2013
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    Here is the circuit on the breadboard: [​IMG]

    what happens is all the digits "sort of" light up as soon as I supply the HV to it. You can still see it cycling through the digits like the test program I wrote is telling it too, but they seem to all be getting a little power regardless. I unplugged all the wires from the microcontroller and it still lights up most of the digits.

    Is it possible that its simply not going to be happy (and work) on a breadboard with voltages of 170-190v? I was able to test it before on a breadboard with a couple of button switches and I could manually light up individual digits flawlessly that way. but the time I did that I used a different breadboard and the IN4 was connected by leads instead of being plugged into the BB itself.

    Thanks!
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,518
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    picture didn't come through.

    ak
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Here is a datasheet for the MPSA42:
    http://www.onsemi.com/pub_link/Collateral/MPSA42-D.PDF
    With the flat face of the transistor facing towards you and the leads pointing down, the emitter is on the left, base in the center. Did you happen to get the leads switched around? If so, you have exceeded the Emitter-Base breakdown voltage (Vebo) by a considerable margin, and those transistors are damaged if not destroyed outright.

    Photo of circuit:
    [​IMG]
     
  4. Bp_968

    Thread Starter New Member

    Dec 25, 2013
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    Thanks for reposting the image, apparently this forum doesn't like using the dropbox "share" links (or dropbox has changed them up so they no longer work properly in forums).

    I'll pull all the transistors and try them one at a time and see if that corrects the problem (at least if i did kill them their pretty cheap, lol).

    Thanks!

    Ben
     
  5. Bp_968

    Thread Starter New Member

    Dec 25, 2013
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    So the transistors were fine (except one of them) but the problem seemed to be that I didn't have a common ground? The 5v was being provided by a separate AC/DC adapter then the HV was coming in on and I didn't tie the grounds together. As soon as I connected the grounds together on both of them everything worked fine.

    I'll be honest, I'm a hobbiest and newb and am not exactly sure what I "fixed". What's going on here that created a problem?

    Thanks!
     
  6. #12

    Expert

    Nov 30, 2010
    16,257
    6,762
    Schematics mean an awful lot here. If you had posted the schematic, several more people might have understood what you needed.

    Grounds are a science unto themselves. After you get through the basics of, "everyone has to know where ground is" you learn about multiple ground loops causing errors, ground current pulses causing errors, frequency dependent ground errors, ground loops radiating like antennas, and a bunch of other stuff. Enjoy the simple stuff. The more you play, the more you will learn.
     
  7. Bp_968

    Thread Starter New Member

    Dec 25, 2013
    21
    0
    I can barely read schematics at this point, much less make them for everything I toss onto a breadboard. :) I was mainly just proving to myself that everything worked and that I had at least a basic idea of how to make the device light up and to make it do that with commands from a microcontroller. Now that I know it all works and I have a better idea of how/why, I'll probably make up some schematics/PCB designs for a basic socket/board for the IN-4 tubes and post them on here to be looked at before I order them.

    The ultimate goal is a clock of some kind using them but I think a module that contains the IN-4 socket and transistors is a better idea then one giant board to hold all 4-6 tubes. At least with the "modules" you can use them on things other then a clock should you so desire.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    Glad you figured out the problem. :)

    Before you start drawing schematics for your modules, have a read through here:
    http://www.electricstuff.co.uk/count.html
    and in particular, read through Ronald Dekker's great site:
    http://www.dos4ever.com/
    There are many articles on Ronald's site that directly pertain to your Nixie desires!
    I happen to have a variety of Nixie tubes myself, and have been considering various options...
     
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