BTW guys, small neon bulbs should have at least 100K resistors (some use 200K) at 170+V or else they could burn out themselves or your circuit. I am able to multiplex them at 170v with a 100K resistor. Remember that the gas inside them will change its resistance until the voltage across the lamp is the sustaining voltage. A 200K resistor (which is probably better for long life) makes them look a little sputtery.
My A1As regulate themselves at 60V, which means that 110V gets dropped over the anode resistor. 110V/100000?=1.1mA. Almost twice the recommended amount, but I figure since I'm multiplexing... Still probably not healthy.
By the way i see that you (wyager) use a lot of transistors for driving your project. Don't you have a 74141 off hand?
ps. the optocouples i need, TLP627, are damn expensive
I was basing my project off parts I could get from digikey and I couldn't find any HV nixie drivers. The MPSA42s were only like 5 bucks for 25 IIRC, so I just went with those. I suppose after the shift registers and resistors and perfboard, the 74141s off ebay would have been cheaper, but it was a learning experience anyway.
BTW, are the optocouples to protect the rest of the circuit from high voltage?
I don't know if this will have contributed to the burnout, but I have discovered that I'd got the pins all muddled.
The power and ground pins were fine, but I had misinterpreted the position of the nixie pins so that I had the number sequence reversed.
I had also failed to spot the utterly confusing layout of the logic pins on the IC. If you look you'll see that the pins are labelled A, D, B, C (in that order). The logic chart is labelled D, C, B, A.
I will have undoubtedly sent things to the IC that it wasn't expecting, though the logic chart says that should merely have resulted in no output.
wyager:
BTW, are the optocouples to protect the rest of the circuit from high voltage?
I need them for multiplexing the nixies. If I connect all the cathodes to the nixie driver IC then I need a way to switch on the 170v anodes. I am experimenting the tlc5940 but I can't let it manage the high voltage. That's way I tought about optocouplers connected to the high voltage anche my TLC to open and close the gate.
CowJam:
I had also failed to spot the utterly confusing layout of the logic pins on the IC. If you look you'll see that the pins are labelled A, D, B, C (in that order). The logic chart is labelled D, C, B, A.
So the datasheed is wrong?? Anyway it looks like a strange way for burning an IC...
Just in time, I was going to ask the same question. I think that no, for what I can understand for driving for example the neon bulbs you have to ground them to the arduino with the high voltage mpsa42 transistor, right?
When I say "running" I mean the nixie lights up and changes and the arduino hasn't caught fire. It isn't doing what I expected in the slightest though.
Edit: Working properly now. I'd not paid enough attention again. Missed one of the ground pins for the 595 and had hooked the 74141 up to shift register pins 1-4 instead of 0-3.
Do I share the ground for the 180v and 5v circuits?
Yes. Ground must be shared between all circuits, just be sure never to share VCC. I suppose you could, theoretically, make separate circuits with optoisolators, but for what we are doing that makes no sense. I have had no problems sharing ground between all of my circuits, just keep the high voltage separate from low voltage through transistors, driver circuits, whatever.
Edit:oops, didn't see there was another page. Glad you figured it out. As you can see from my schematic (I think I posted that here) I'm just driving a bunch of MPSA42s from a shift register.
Progress report:
I've set up four 74141s and two shift registers (595s), but am running two nixies so far, and a bulb.
I'm using a spare PC PSU for power, the arduino is the one I fried so it needs to be powered from USB. I'll be adding a USB plug to the PSU as soon as I've been to maplin to buy a male type B plug.
Here's some pics:
Nixies:
Click for Big.
The rig (using a bit of Meccano to make a gantry to hold the nixies):
Top view:
At the top is the 12v - 180v PSU.
Coming in on the right is a 5v line and a 12v line from the PSU.
The breadboard is 74141, 74141 and 595 (in use) and the same again waiting to be hooked up and an IN-35 bulb.
The arduino is sat on a bit of polystyrene and attached to the gantry.
The nixies are in sockets suspended from the gantry.
I am getting a bit confused.
You guys said that optocouplers are not necessary if I am going to multiplex the nixies.
In your setup aren't necessary because you hook up the anode and use a 74hc595 with two 74141 for 2 nixies. So if you have 6 nixies you have 3 595 and 6 74141, at least.
But, if you, for example, connect all the cathodes of your nixies together to a single 74141 you need to switch the anodes with the 595, in high voltage multiplexing them and using persistence of vision. I supposed that this was the meaning of the transistor, for dividing the high voltage of the nixies from the low voltage of the IC's and the arduino...