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K155ID1 chip showing low voltage between decimal pins and power supply. Is the chip bad? Answered


I turn to those who know probably a heck of a lot more about this than I do. 
I've been trying to build myself a nixie tube clock, and everything has been going fairly well. I recently got the driver chips in the mail which convert BCD -> Decimal in order to hook the nixies up to a digital logic system like an arduino.

I'm using a 12 V -> 180 V switching power supply for lighting the nixie tube. It is connected to ground on a computer power supply that I'm using to power the entire project. The 5 V rail on the computer power supply is connected to the Vcc pin of the K155ID1 chip as shown in the picture. I've connected the ground pin on the K155ID1 to the common ground of the computer power supply. I have nothing connected to the A, B, C, or D pins on the driver chip, which from what I understand should be the same as inputting the BCD number 0000 or just 0 in decimal. If I'm inputting a 0 as my number, the chip should output a 0 in decimal. From every single datasheet I've seen talking about this chip, that should mean that pin "0" (as shown in the picture) should become effectively grounded, and assuming that the "0" pin is connected to the 0 digit on the nixie tube, that should connect the nixie tube to ground, which should allow 180 volts to flow through the nixie tube, causing it to light up.

Unfortunately, this is not what happens. In fact, nothing happens. Nothing happens no matter what pin on the driver the nixie tube is connected to. The only way I can get the nixie tube to light is if I connect it directly to ground, in which case, it lights up very nicely, but obviously that doesn't help with controlling it in any way. I took out my multimeter and measured the voltage between the 180 V supply line of the nixie tube and the pins of the driver chip, and every single pin (except A, B, C, and D) show a voltage of about 80 volts, which is not enough to light a nixie. 

My question is, is there something I'm missing? I would think that the chip was bad or that I popped it or something. Heck, you could fill an electronics graveyard with all the chips I've popped over the years. But I've rebuilt this setup 4 times now, and I've attempted this following multiple schematics, and even switching the chip out for a brand new one 5 times. Each and every time the result is exactly the same. Either I'm overlooking something huge, or I just happened to buy 10 dead nixie driver chips.

Thanks, in advance for any input!


TIE your inputs to ground, and see if the ZERO character lights: leaving pins floating is a very bad idea in general.

Well, sure enough that did it! Thanks a million! One last thing though:

When I was driving this circuit with an arduino originally (shown in picture) it didn't work. Would I have to use transistors to connect the pins to ground when not in use then? The only thing I noticed during these tests that might have something to do with it not working is the fact that the arduino was only putting out 3v to the driver inputs, whereas now I've got 5 volts on the inputs.


All you need to do is physically tie the unused pins to ground.

The arduino should have worked. Check your grounding. The Vih figure (what voltage = logic 1 is 2V according to the data sheet.

You COULD use transistors to make your pins run 0..5V, not 0..3V, but you could use a 74HCT245 gate instead. It will convert from 0..3V to 0..5V logic for you quite nicely.

Alright, here's what I've got set up. To clarify a few things:

- The first picture is the schematic of the 12v -> 180v converter. The second is the circuit I currently have set up.

- The 5v and 12v rails on the power supply share a common ground.

- The ground on the 12v -> 180v converter is shared by the 12v input and the 180v output.


Is the hotside ground common to the low side on your high voltage supply, or does it need to be tied to the other ground/

Post your whole schematic, and a link to a datasheet. Make it easy for us to help