This article is very old, from around 2006. It was originally published on my old website, flylab.ovh.org, now defunct. It’s unlikely to have much educational value. I’ve republished it mainly for sentimental reasons. Grammar and style were left “as is”.
Here is a description of the pyrotechnic detonator I made. It was designed for safe, remote detonation of petards, fireworks etc. using electricity. It’s made of an old Polish military field telephone (type MB66). I took the inspiration from one of the Polish chemistry webpages, but my version has got additional accessories, like charging control, line continuity tester and capacitor’s discharger.
Someone may ask, why did you build a complicated device, as is possible to launch and igniter made of lightbulb using an ordinary battery. So if you use this device,
- you could fire the igniter distanced two kilometers from you
- you can use other igniters, like thin cooper wires and professional ones
- you look more professional :-)
List of components
- field telephone or generator
- capacitor set >1000 μF 200 V, e.g. from old PC power supplies
- thyristor 20 A 200 V or bigger one
- two standard 230 V switches
- two push-buttons, red ones are the best
- power resistor 2 kΩ 5 W
- Zener diode 5 V, Zener diode ~160 V (a few ones connected in series), depend on your generator’s voltage
- bridge rectifier 1 A 250 V
- two diodes 200 V/1 A
- two LEDs - red and green
- resistors 0.5 W: 150, 470 and 500 Ω
- resistor 10-100 Ω, that depends on thyristor’s ignition current
- transistor NPN BC548 or similar one
- battery 9 V and connection
You don’t need the whole telephone, but only the ringing generator, otherwise called inductor. It’s used to generate a ringing signal. But the complete telephone is a better solution, because you become a nice case and terminals. I bought mine on certain online auction website. It was very cheap. You can see it in the pictures. Disassemble everything except the generator and output terminals. You can also get the generator from an old insulation meter or even use a bike dynamo with transformer (for example 230 V -> 9 V).
Schematic and assembly
The capacitor set is made of 4 capacitors 330 μF 200 V, so together they have got 1320 μF. The wires capacitor-thyristor-terminals should be thick. The resistor connected to thyristor’s gate should have the highest resistance when the ignition still reliably happens. In my device, it has only 10 Ω. S3 is a main trigger button. S4 protect of an undesirable ignition.
Line continuity tester
It tests if the line detonator-igniter is broken. If it happens, the LED diode should light up when the S2 is pushed.
Charging control
The green LED indicates if the capacitors are charged. While you’re cranking, it should light after a few seconds. You can change the maximal voltage using different Zener diodes D2. I used five 33 V diodes connected in series, so the voltage is 165 V.
You can check if you built your device correctly. Connect a 230 V 15 W lightbulb to the terminals, then charge capacitors and press the trigger. It should light for a moment.
Igniters
You can use small lightbulbs from Christmas tree or torch as igniters. It’s also possible to use a thin copper wire.
Remember! Use this device in compliance with the law and common sense.