How to Drive Nixie Clock

Good day,all.

I am a student who majoring in electronics and I am currently working on my first nixie clock which will be running with Arduino, using a 74141 nixie driver for the cathodes (common for 6 tubes) and multiplexing the anodes.

See the following picture:

I am using a MPSA42 NPN transistor with the collector connected to +170VDC, the base driven by the Arduino output, and the emitter connects to the tube’s anode. The problem is that the switching with the MPSA42 doesn’t seem to work (doesn’t turn ON).

MPSA42 Datasheet

However,such as this picture:

I saw some other design which used both MPSA42 and MPSA92 each of the six anodes like it.My questions:

  • l What might be the reason why the single MPSA42 configuration would not switch ON?

  • l Why would the other design add the MPSA92 and whats the logic behind using the MPSA42 + MPSA92 combination?

PlePlease give me some help! Thank you in advance!


If you do not understand why your single transistor circuit does not work, then I suggest you go read up on “emitter follower” circuits and then think about why they are not appropriate in this circumstance.

I suggest you use the second circuit, with the two transistors, and go take or repeat a class on semiconductor devices.

I would also add a “pull-down” resistor to the input of the first transistor in the two-transistor circuit, so that it can not turn on when the driving circuit is not initialized, and “floating”.

— Graham