Neon heads/tails. By Lee Davison.

This wasn't the first project I ever built but it was the first one that was ever finished completely, case and all. I think I was around ten years old at the time and the fact that it is in a box is probably the only reason it has survived for more than CENSORED years.

Everything used to build it was 'recycled' from something else. The case was a cigar box from my grandfather, the resistors, diode and one capacitor was from a TV - which was old even then - and the rest of the components where from a gutted juke box that was in a back room at the local Church House. The lampholders were 'recovered' from car dashboards at one nearby scrap yard.

Construction is nothing to be proud of, unless you were ten when you built it and you had no help with any of it as no one else in the family was interested. That I even had access to a soldering iron was more luck than design. I used to use a lot of solder then.

The box is also probably the only reason it never killed anyone, this circuit is dangerous and I wouldn't build one like it now. It is presented here for information only and no one should try to reproduce it - ever.

The circuit is a fairly simple thing. R1 limits the current should it all go horribly wrong, just not enough to make it safe. D1 and C2 form a DC supply of about 380v, far more than this circuit needs to work.

With SW1 open when the circuit is first powered C1 is discharged and one of the neons will strike. This will lower the voltage across both the neons preventing the other neon from striking. As the voltage across the lit neon is fairly constant C1 will begin to charge via the 1M resistor connected to the other neon. Eventually C1 will charge far enough for the other neon to strike and, as C1 is now charged, lower the voltage across the lit neon causing it to extinguish. The process will now repeat but with C1 charging through the other resistor.

When SW1 is closed C1 will be discharged and whichever neon was lit at that point will remain lit. Opening SW1 will allow the circuit to start oscillating again.

I don't think any of the component values are critical, they just need to be able to handle the voltage. C2 can be polarised as it only ever sees DC but C1 must be a non polarised type. R2 and R3 should be the same value and NE1 and NE2 should be the same type. The circuit will work with D1 either way round and the original mains plug was a two pin non polarised type, which I think I later stole for use on something else.

Last page update: 1st September, 2012.

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