Arduino Multiplexing

Posted on Feb 4, 2014

The Nixies I`m using have 10 cathodes (shaped like numerals) and a screen-like anode. These are old Russian IN-12A`s that I obtained from an excellent Ukrainian shop on eBay. Other Nixies might have more cathodes for a decimal point or other symbols (like the IN-12B shown below). Since it`s not important to show which pins connect to which cathodes for the following diagrams, I`m going to show

Arduino Multiplexing
Click here to download the full size of the above Circuit.

all the cathodes as one and just notate that there is a 10-line bus going into the tube. Similarly, the 74141 or Russian equivalent decoder chip, which translates a four-bit nibble into one of ten output pins, will be shown as a simple rectangle with a four-line bus going in and a ten line bus coming out. So, let`s dive into the schematic. (you can see a small copy here or at Now, as an alert reader pointed out, there`s a typo  on the ArduniNIX schematic in the anode drivers the MPSA42 is shown with a PNP symbol instead of the NPN device that it is. But don`t worry the circuit actually works the right way. Here`s a simplified diagram of one anode driver circuit that shows the transistors but omits the biasing and current-limiting resistors. When your software turns on the output pin to enable the anode, the MPSA42 at Q1 amplifies the microcontroller`s wimpy little output current and turns on the MPSA92 at Q6. These are high-voltage transistors and they are able to supply current to the Nixie tube at the high voltage it requires. It doesn`t need much current, only a few milliamps, so they don`t need to handle a lot of power. It`s the breakdown voltage that`s the important parameter. Now, I`ve shown the cathode side of the tube as going straight to ground. In reality, the circuit uses a 74141 high voltage decoder (or Russian K155N equivalent). This circuit converts four bits, presented simultaneously by four Arduino output...

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