arduinointegrated-circuitnixie
I am using NTE74141 chips to connect the cathodes of nixie tubes to ground. To spare some Arduino pins (which I connect to the inputs of these ICs) I would like to multiplex the tubes. One idea was to simply make all inputs of the ICs the same, and essentially turn on and off the ICs by connecting it's Vcc to ground using a different Arduino pin.
This setup seems to be working fine, but my question is: is it damaging for ICs to connect it's Vcc to ground, and if so, why?
Yes, all the components need to share a common ground (if you're paranoid you can have the high voltage ground connect to the low voltage ground in one place through a ferrite bead). The "outputs" you're talking about for the BCD are just acting as switches to ground, so they don't experience the high voltage and small current on the same time. When turned on (switched to ground), most of the voltage is dropped on the Nixie tube segment and series resistor. When switch off however, they'll see the full voltage. It's difficult to tell from the linked data sheet what voltage they can handle, the part that's in English talks about a DM54/DM7441A, while the Russian part looks like it's about the K155ID1s. The two parts of that datasheet can also be found independently online, so I'm not sure if they're supposed to be pasted together. It certainly looks like people have been using these with 170VDC, so they very likely work, though the lifetime may be degraded. I'd say go for it, the chips are only $0.90 some places.
The nixie tube is essentially the same as a neon bulb with multiple cathodes. The wire cathodes are shaped into the numbers 0 to 9. To turn the electrode ON you need to supply a high voltage (of about 170 Volts DC)to the common ANODE (the see through grid). This will be through a current limiting resistor to give a current of about 2mA. When 'lit' the anode voltage will drop to about 140V (the maintaining voltage). You will need to check the actual figures for your chosen nixie tube.
To light the cathode you will need to switch it to ground (0v) through a transistor or other suitable switching device.
This could be done by switching each cathode with a single I/O line (through suitable transistor etc.) but with three nixie tubes you would quickly run out of lines.
This is where the 74141 comes in. It is a BCD decoder 1 of 10 outputs designed to switch the cathodes of the nixie to ground. This requires FOUR I/O lines per digit (nixie tube). This chip also ignores non valid numbers (1010 - 1111) and blanks the display.
You could drive this chip directly from the arduino OR you could add some 4 bit latches between the arduino and the 74141 avoiding the need to tie up the I/O lines or multiplex the display.
Health and safety warning - High voltage hurts and destroys arduinos if you're not careful.
Best Answer
One idea was to simply make all inputs of the ICs the same, and essentially turn on and off the ICs by connecting it's Vcc to ground
That's a BAD idea and I'm sure that it will not work.
Why? Because almost every chip has input ESD protection circuits like this:
Note top left the diode between VIN and VCC.
In your proposal VCC would be grounded, that means any positive signal applied to VIN will make the diode go into forward mode. This will load the VIN line which is your "databus" limiting the voltages to about 0.7 V. This means your "databus" will not work anymore.
A better solution would be to use a PCF8574 based solution which gives you many pins controlled from a single I2C port on the Arduino. There are many example schematics to be found using this solution for driving a 1602 LCD module from an Arduino.
Edit:
The NTW74141 does not have a very extensive datasheet.
I found a datasheet of the (original ?) Texas Instruments part it was based on, the SN74141. This does show an input circuit which is a bit different from the 2 diode ESD protection:
If the circuit really is like that also on the NTW74141 then the issue I described above does not happen and what OP proposes (enable/disable via supply rail) could work. It is still not an elegant solution but it could work.
You could also use the diode-test of a multimeter to check if the ESD diode is present between input an Vcc as in the first picture or not.