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.
The pyrotechnic detonator I made is designed for the safe launching of fireworks and rockets using electricity. It is constructed from an old Polish military field telephone, type MB-66. I took inspiration from a Polish webpage about chemistry, but my version includes additional accessories such as charging control, a line continuity tester, and a capacitor discharger.
Someone may ask why I built a complicated device when it is possible to trigger the igniter made from a lightbulb simply with a battery. My motivation was as follows:
- You can fire the igniter from a distance of up to two kilometers.
- You can use various igniters, such as thin copper wires and professional initiators.
- Turning the crank and firing is fun; we do fun here, don’t we?
Field telephone MB-66
MB-66 is a Polish military field telephone. As it is a local battery telephone, it needs a 1.5 V battery to work. Pieces of this telephone were used almost 15 years later in my making of my Octoglow device.
List of components
- Field telephone or just a ringing generator from it.
- Capacitor set of at least 1000 µF 200 V, e.g., from old PC power supplies.
- Thyristor 20 A 200 V or a bigger one.
- Two standard 230 V switches.
- Two push-buttons.
- Power resistor: 2 kΩ 5 W.
- Zener diode 5 V, Zener diode ~160 V (a few connected in series), depending 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, depending on the thyristor’s ignition current.
- Transistor NPN BC548 or a similar one.
- Battery 9 V.
You don’t need the whole telephone, but only the hand-cranked ringing generator, otherwise called the inductor. It is used to generate a ringing signal. However, the whole telephone is a better solution because you get a nice cabinet and terminals. I bought mine on a certain online auction website. It was very cheap. 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 a transformer (for example, 230 V -> 9 V).
Schematic and assembly
The capacitor set C1 is made of four capacitors 330 µF 200 V salvaged from ATX power supplies.
Together, they have a capacity of 1320 µF.
The wires between the capacitor set, thyristor T1, and the output terminals OUT should be at least 2.5 mm² cross-section.
The resistor R5 connected to the thyristor’s gate should have a resistance that allows the thyristor to ignite reliably.
You should match it to your thyristor.
In my device, it has only 10 Ω.
S3 is the main trigger button.
S4 is in series with S3 and acts as a safety device, so you can’t fire the detonator accidentally.
You should switch it on just before you want to fire.
Line continuity tester
It checks if the cables between the detonator and the igniter are not broken.
If you press button S2 and the red LED lights up, it indicates that the line has a break.
You can also test the battery this way.
Charging control
The green LED shows that the capacitors are fully charged.
It should light up after a few seconds of cranking.
The maximum voltage is determined by the Zener diodes D2.
I used five 33 V diodes connected in series, so the firing voltage is 165 V.
Testing
To test the device without using live igniters, you can use a 230 V 15 W lightbulb. Connect it to the output terminals, check the continuity, charge the capacitors, and press the trigger. The lightbulb should light up for a moment.
Igniters
You may use various low-voltage incandescent lightbulbs, for example, from Christmas lights or flashlights. It is also possible to use a thin copper wire as an igniter.
Remember! Use this device in compliance with the law in your jurisdiction and common sense.