Have you ever wanted to light something on fire from far away? Well, that's exactly what this project is, a means to remotely light things on fire via two PICAXES and an RF link RX/TX pair. This system is mainly intended to launch model rockets, and can do so from over a hundred feet away! It's also able to light things like thermite, fireworks, explosives... anything you need on fire, and would want to stand far away from. PICAXEs are only a few dollars, so if your experiment goes awry, you'll only lose a couple dollars instead of injuring yourself.
As an added touch, I decided to put a 7-segment display on my transmitter so I can display words, a countdown timer, etc. However, I obtained my display from an old DVD player, so my system likely has a different pinout than yours. Keep this in mind if you decide to add one yourself.
To test the system, my friend PopsicleGhoul and I made some sugar rockets, then launched them off with the system. It worked perfectly, although the rocket did not perform so well... perhaps next time. We did get some cool footage from his onboard camera, however, which you can see in the video below.
WARNING! This project involves the use of high-current batteries and matches, which may light on fire unexpectedly if not handled properly. Use caution and common sense when building this project. Should you attempt this project, you assume all risks of injury that may arise when building this project!
Remember, this system is a DIY igniter and is not necessarily perfectly stable. I have had no misfires, but I cannot guarantee that any version of this ignition system will not misfire or fail to ignite. By using this ignition system, you assume all risks of misfire or failure, and all consequences thereof.
Additionally, objects such as rockets and explosives are DANGEROUS, and may be illegal in certain countries/states. Again, exercise caution and common sense when igniting said objects, and do not forget to check local laws governing the use of the object you intend to ignite. Should you use this system, you assume all risks and consequences involved with the object you intend to ignite.
Step 1: Materials
To build your own RF rocket ignition system you will need:
- 1x PICAXE 20M2 (for the transmitter)
- 1x PICAXE 08M2 (for the receiver)
- 1x Sparkfun 434MHz RF link transmitter
- 1x Sparkfun 434MHz RF link receiver
- 1x 5-in-1 7-segment display (this is optional)
- 2x 3.5mm audio jack sockets
- 2x status LEDs
- 2x 0.1uF capacitors
- 2x 100uF capacitors
- 1x 1M resistor
- 2x 10K resistors
- 2x 22K resistors
- 4x 200Ω resistors
- 2x L7805 voltage regulators
- 1x IRFZ44N power MOSFET (or other N-channel MOSFET capable of switching high amperage at 18V)
- 2x power switch (optional, but recommended)
- 1x 18V Ryobi One+ drill battery (or other high-current portable battery)
- 1x 9V battery
- 4x alligator clips
- Some wire
- Some solid-core wire for the RF link antennae (optional, but drastically increases range)
To program the PICAXEs you will need:
- 1x AXE027 3.5mm serial programming cable
- 1x computer with the PICAXE editor installed (PICAXE Editor 6 for Windows, and AXEPad for Mac/Linux)
To make the electric matches you will need:
- Some stranded copper wire
- A sharp knife, e.g. an X-Acto knife
Step 2: How It Works
At its heart, this project is two PICAXEs communicating via an RF link. The transmitter PICAXE waits until the launch button is pressed, then signals the receiver PICAXE. The receiver PICAXE then triggers the power MOSFET, which dumps loads of current into an electric match, igniting it and launching your model rocket.
The basic operation is simple, but I decided to add a 7-segment display to the transmitter, which significantly increased the project complexity. My 7-segment display has pins to control which segments are lit, and which digits are selected. To display an "8", all of the segment selection pins must be set HIGH, while the required digit selection pin must be set LOW. This displays an "8" on whichever digit I choose. Simple.
The difficult part is when multiple digits need to be lit. Since there is only one set of segment selection pins, if multiple digit selection pins are set LOW, the same number will be displayed on each digit. This is similar to the ghosting effect that can be found in LED cubes, and can be solved in the same manner: multiplexing.
To multiplex, each digit of the display is lit up, one at a time instead of all at once. By cycling through the digits extremely fast, the human eye will not be able to perceive the change and the entire display will appear to be lit at the same time. This phenomenon (called persistence of vision) is the principle behind LED cubes, and it will work for our purposes here, too.
Step 3: Wiring the Receiver
Let's start with the receiver, since it's simpler than the transmitter. You can see the receiver schematic above. I suggest adding a switch between 18V and the L7805, although this is not necessary.
I built my receiver on a half-breadboard, that seemed to be the smallest I could get it. You don't have to build yours as small as possible, but the smaller you can get it the better.
While researching these RF link modules, I came across a forum thread that suggested grounding the RX linear output pin via a 1 megaohm resistor. I tried it with and without the resistor and saw no noticeable change in operation, but I left it in anyway, just in case.
Here is the datasheet for the RF link receiver.
Step 4: Wiring the Transmitter
Next, wire the transmitter according to the schematic above. I suggest putting a switch between 9V and the L7805, although this is not necessary. With the 7-segment display, I was able to fit the entire circuit on a full-size breadboard, although without it the circuit would probably fit on a half-breadboard.
My 7-segment display needed 13 control pins, and with the 3 pins for RF control and 4 for operation, I ended up using all twenty pins on my PICAXE 20M2. Just be careful if your 7-segment display needs more control pins, you may have to buy a bigger PICAXE (a 28X2 or 40X2).
Here is the datasheet for the RF link transmitter.
Step 5: Test the RF Communication
Now that your circuit is complete, it's time to make sure the RF communication is working properly. Upload the RFReceiverRocketLaunch.bas to your receiver PICAXE 08M2. For the sake of testing, just use a 9V battery to power the receiver for now. Later on it will be powered by the 18V drill battery.
Upload the RFTransmitterPing.bas to your transmitter PICAXE 20M2. Turn the transmitter on, and the LED should begin pulsing at an interval. Each time the LED pulses, the RF transmitter should be sending data. Now turn the receiver on, and the LED should begin blinking at the same time the transmitter LED does. Congratulations, your RF link is complete!
This is also a good time to test the range of your modules. Set the transmitter somewhere safe, then walk around with the receiver while watching the LED. It should blink in a regular pattern, and if it misses a blink, that means it missed a data transmission. See how far away you can take the receiver without it missing any transmissions.
You can also add an antenna to greatly improve the range. I used approximately 5in lengths of solid-core wire as my antennae, and these boosted my range from around 20ft to over 200ft! Not all RF link RX/TX modules are the same, though, so you may have better or worse range than me.
Step 6: Program the Transmitter
The circuit is complete and the RF link is functional; now it's time to finalize the transmitter. Depending on whether you added a 7-segment display or not, upload either the RFTransmitterRocketLaunch.bas or the RFTransmitterRocketLaunchNoDisplay.bas to your receiver PICAXE 20M2. Remember, unless your 7-segment display has the exact same pinout as mine, you will likely have to edit the code (RFTransmitterRocketLaunch.bas) to reflect those differences.
If your transmitter uses the 7-segment display, it will display "ARMED" while it waits for you to press the button. Once you press the button, it will count down from 10, then display "LAUNCH" while it transmits to the receiver.
If your transmitter does not use the 7-segment display, pushing the button will cause it to immediately transmit to the receiver.
Step 7: Set Up the Drill Battery
Ryobi batteries provide plenty of power, but are difficult to connect to. I made the connection process easier by taping two pieces of scrap aluminum onto the battery terminals. This allows alligator clips to clamp on to the battery and is non-invasive, meaning the aluminum can be removed and the battery can still be used for tools.
If you don't have any pieces of metal, you can tape or clamp the alligator clips to the drill battery.
Step 8: Make the Electric Matches
What is an electric match? Simple: an electric match is a match with a thin wire attached to the match head. When large amounts of current are run through the wire, the wire heats up like a filament, which ignites the match.
The match design I used is based on Grant Thompson's electric matches, although I have not been able to ignite my electric matches with 9V batteries. Perhaps you will have more success than me; I ended up just using a Ryobi One+ battery.
Use your X-Acto knife or other sharp knife to cut a notch in the top of one of your matches. Then strip the insulation off a 2-3" length of thin stranded copper wire. Take one of the strands and tape one end to the match, leaving about 1/2 cm of wire beyond the tape. Bend the wire over the match head, so that it runs through the notch in the match head. Finally, tape the other side of the wire to the match. You should have a thin wire running over the head of your match, with two exposed wires by the match stick.
You can test the electric match by taking your high-current battery and connecting the two match wires to the two battery terminals. If all goes well, when the wires are connected, the match will burst into flames.
WARNING! Be careful when testing your electric matches, as they can burn you if not handled properly. Hold the matches by their wooden base, or clamp them in a vise to prevent harm!
Step 9: Final Steps
Now that the drill battery is set up, use alligator clips to connect it to the receiver, in place of the 9V battery used for testing. Use alligator clips to connect one wire from the electric match to 18V+ and the other wire to the IRFZ44N source pin.
And you're done! At this point your remote ignition system should be fully functional. I suggest doing several ignition tests to make sure that the match lights every time. Once you are confident that your system is reliable, you can use it to launch rockets and light fireworks to your heart's content.
If you want to take this project a step further, you can try using a larger receiver PICAXE for more control pins (and more electric match controls). You could then light several rockets simultaneously, or with a spaced delay. You could even set up your own fireworks show using the PICAXE transmitter as a controller!
I'm always happy to hear any comments/suggestions you have, and if you happen to have a question, feel free to send me a message or leave a comment and I'll see if I can help. Happy rocketeering!