A recent discussion with my friendly editor, Adam Carlson, rekindled my idea of designing an unusually simple, yet highly useful, radio remote-controlled firecracker for upcoming festivities. Because the design should be submitted within a stipulated time frame, I shamelessly looked for a shortcut and bought two pre-wired RF transmitter and RF receiver boards from eBay. The quick move helped me to rig up the first version of my RC firecracker within a couple of minutes. Here are the complete project details that allow you to ignite firecrackers from a safe distance!
In principle, the circuit comprises three equally important key parts: an RF transmitter, RF receiver, and electronic igniter.
The compact radio-frequency transmitter and receiver module package from eBay is, in fact, a 434-MHz (actually, 433.92-MHz) wireless remote-control system. The RF transmitter consists of a 434-MHz license-exempt radio transmitter module and an encoder chip HT12E, while the RF receiver consists of a 434-MHz radio receiver module and a decoder chip HT12D. In case you are facing difficulties in getting this specific item, you can build your own circuitry (on perfboards) by following the open-hardware schematic (shown below) rendered by the eBay seller (B.M. Embedded Solutions, New Delhi, India). Also watch their intro video available here: https://youtu.be/8TO28vYdlsQ. However, note that the aforementioned schematic is a canonical one, somewhat different from the actual schematic of the item listed by the eBay seller!
The “red-hot” part of the project is an electromagnetic relay controlled heating wire/fuse. The circuit diagram of the electronic igniter shown above is straightforward and self-explanatory. Here, galvanically isolated electromagnetic relay driver circuitry is used to control the heating element/fuse (1.5 in. of 40AWG Nichrome80 wire) from the output of the RF receiver. Because the RF remote control has four independent channels (pins 10–13 of HT12D IC in the receiver), you can replicate this electronic igniter circuitry to build multiple (four) heating lines. However, as 1.5 in. of 40AWG Nichrome wire draws current close to 1.5 A, without a healthy 12-V battery, the electronic igniter probably couldn’t ignite a firework on its output channels.
If you follow the schematic published by the eBay seller, the first version (v1) of my electronic igniter circuit (shown above) will work with it. But the RF receiver board that I got from eBay gives active-high (H) outputs at its D0–D3 channels (pins 10–13 of the decoder chip). If you’re in the same boat, try the second version (v2) of my electronic igniter circuit (shown below). In both versions, you may need to alter the value of the 1K resistor (R1) for optimum performance!
My prototype was tested with a 9-V PP3-type battery as the power source of the radio transmitter and a 12-V/2-A lab power supply as the power source for the radio receiver and electronic igniter. With the limited free space there, I didn’t want to risk being responsible for a fire that burned my lab. So I just fired only a couple of homemade fuses as the proof-of-concept.
Fireworks are illegal in many countries. Before you go lighting off fireworks, check for any local restrictions. Stay safe!