Disposable Camera Nixie Tube Driver

Step 3 Attach wires.

To make this circuit more convenient to use, it is time to add some wires. Notice the capacitor has a stripe on it. The black wire will connect to the lead beneath the stripe, and the red wire will connect to the other lead.

Comments

[Halt! I am Reptar]

Does the charge button need to be shorted?

[the_don125]

This camera actually had an on-off switch for the flash, rather than the more common "button" design. I didn't have to short anything, but rather used the on-off switch as a power switch for this power supply. I liked having that feature rather than having an "always on" supply that would've resulted from shorting the charge button.

[Halt! I am Reptar]

I had to solder the charge button closed to get my Nixie to light up, i dont think you mentioned that. Maybe yours doesnt use a charge button? I got some modern Kodak ones from Walgreens' recycle box.

[sci4me]

So I can just discharge the cap and then cut it off as long as the wires are connected to the circuit?

[the_don125]

Sure, that is probably a much safer way to use this circuit.

[DrWilliamHorriblePhD]

I've heard rumor that replacing the cap with a diode is a preferred solution, but I don't actually know why, nor what orientation to place the diode in. Thoughts?

[the_don125]

You would want a diode rated for 200V reverse breakdown voltage, connected "backward" so that it would not normally conduct.
Why?
Well, the diode would prevent current from flowing as the circuit powers up. However, nixie tubes like to be driven around 180V, more than that and you might put too much power through them, shortening their lifespan. The diode will start conducting backward when the circuit is at 200V, ensuring the circuit stays at or below 200V. This does improve safety somewhat as well.

Now, with this circuit's approximate internal resistance of 15k, that means the internal resistance must dissipate 100V (the diode drops the other 200), for about 6mA of current. This results in the diode dissipating 200V * 6mA ~ 1.3 W of power, so get yourself a diode rated for 2 or more Watts of power dissipation, and you'll be set!

[grstearns]

Wouldn't holding the shutter button down for a few seconds be enough to discharge the cap so that it would be safer to open?

[the_don125]

Not always. The gas discharge tubes that make up a camera flash work on the same principle as the nixies in that they will operate down to a certain voltage, then stop conducting. The point where they stop conducting will often leave a fairly high voltage still in the capacitor.

[sci4me]

Alright, i'll try it sometime.