I know enough to be dangerous, i can build circuits and make minor changes but i am not an expert. I put this together after looking at schematics i have found online and i need some help getting the right components. The individual components i cant take credit for but i think the idea and final unit will be unique.

This is a speedometer for my 1950 Studebaker. It is a modern charging/ battery system. Should give between 11 and 14 volts. Both power supplies i have, the avr i am familiar with and have, i used it to control a skeeball machine. It uses a pulse generator on the transmission (new Dakota digital sen-01-1), i then modified the self powered sine to square wave circuit to run off of available power. I am hoping this will make it more sensitive. I am using the Russian equivalent to the Nixie drivers 74141.

1: i would like to control 2 of the elements without the need for a chip what should i do here? (mpsa42 and a 33k resistor? I have!)

2: Between the at mega avr and the 74141 (K155ID1)? do i need anything?

3: Do i need to do something special on the input voltage for these 74141 s?

4 and 5: I would also like to use ne2 lamps to replace my hi beam and left and right turn indicators. These are roughly a 12v signal i have 5v and 170v what circuit should i use? Hi beam may be on for long times. (tip 102?)

6: (not numbered on schematic) Is my use of the sine to square appropriate.

MY hand drawn schematic: http://i871.photobucket.com/albums/ab280/FortyTwo-edo/nispedov1.jpg

Sorry this is long but i have been looking at this for awhile and finally need to get it prototyped before snow so i can test it before i build the case.

Thanks Ed Owens

  • \$\begingroup\$ sine to square: redcircuits.com/Page17.htm \$\endgroup\$
    – Ed Owens
    Commented Oct 1, 2010 at 22:00
  • \$\begingroup\$ good Nixie data: tube-tester.com/sites/nixie/74141-NDT/74141-NDT.htm \$\endgroup\$
    – Ed Owens
    Commented Oct 1, 2010 at 22:01
  • \$\begingroup\$ Just got sending unit hooked up at 70 ish i was turning 180 hurtz and about 4.2 v ac. I figure this should be able to handle at least 6 volts whitch i should never exceed. \$\endgroup\$
    – Ed Owens
    Commented Oct 2, 2010 at 19:49

1 Answer 1


1) I used MPSA42 transistors as low side switches in my Nixie tube clock. A 10K current limit resistor on the anode of the tube and (as I recall - schematics not at hand) a 68K resistor on the base of the transistor. The MPSA42 components are cheap enough that you can experiment with them.

  • \$\begingroup\$ My transisters are extras left over from my nixie clock. IT had a 33k resister on the signal wire and thats it. Thanks \$\endgroup\$
    – Ed Owens
    Commented Oct 2, 2010 at 19:48
  • \$\begingroup\$ @Ed Owens did you make hack-a-day or something like that for your nixie clock? Or did you just copy their idea? \$\endgroup\$
    – Earlz
    Commented Dec 13, 2010 at 22:57

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