This build will require basic electronic and soldering skills along with ability to use a drill or dremel. If you are under 18 years old you should do this under the supervision of a responsible adult - get dad to help out!
Warning: You are participating in this project at your own risk. I am not responsible any injuries or damage to property as a result of your actions. I recommend using all safety precautions available including working in a well ventilated area, with safety glasses on and other protective equipment. Its not worth hurting yourself because of taking shortcuts in safety!
Step 1: Tools and Supplies
- Adjustable spanner
- Soldering Iron and Solder
- Dremel, portable drill or drill press
- Plastic Casing - I used a 197 x 113 x 63mm ABS box - I got mine from jaycar for $7 AU but I would recommend a hinged box as you'll be opening and closing it to change out batteries - see here
- Two channel radio frequency [RF] receiver - Similar to garage door remote control - I found a four channel one here for $11 AU including free shipping
- One 12v "rocket" switch
- Three Nine Volt Batteries*
- Eight AA rechargeable batteries*
- Three Nine Volt Battery Connectors* - 90c each - see here
- One eight AA battery holder* - About $2 each from Jaycar - see here
- One red and one green 12v LED indicator lamp - about $3.50 each - see here
- Length of speaker wire - I used three metres but you may want to use shorter or longer depending on how far away you want the igniter box from your rocket - something similar to this.
- Various lengths of electrical wire - I had mine lying around from past projects - you probably want red and black to make it easy to identify positive and negative when soldering.
- Aligator Clips - you might want to buy these cheap and in bulk because they are going to get toasted every launch!
Step 2: The Circuit
I'm not very talented when it comes to electronics, but this projects should be relatively easy for beginners or experienced persons alike with limited electronics experience required to complete it. In looking into the RF receivers available on eBay etc it appears they all have pretty similar layouts. The one that I bought had four terminal blocks, each with three screw in terminals labelled "1, 2 and 3" and one terminal block with two terminals devoted to powering the circuit.
I had two 9v batteries powering the circuit - this should be pretty easy to work out as it will have a positive and negative symbol printed below the blocks. One nine volt battery didn't have enough current to power the circuit thus I used two. Wire up your 9v battery clips in parallel (positive to positive and negatives to negative) then screw the positive wire from your batteries into the positive terminal. The negative wires run from the battery through a switch then into the negative terminal. This switch allows you to turn power to the circuit off.
The way the next three terminal work is the negative cable from the power source goes to terminal "1". Terminal "2" is your negative cable to your LED and firing leads [components]. Terminal "3" is both your positive cable from your power source and the positive cable to your components.
You want the positive cable from your power source going straight to terminal 3. Also screwed in to terminal 3 is the positive wire to your "armed" LED and either one of the ignition leads. The negative cable from your power source runs through the same switch used earlier to terminal 1. A wire should run from terminal 2 to the negative wire for the "armed" LED and to the other firing lead.
You basically now have the circuit needed to cause ignition to your e-match, but as a safety feature you want to wire in another power source for another channel on the RF receiver. This will represent when the circuit is in "safe" mode and you can connect your firing leads to your e-match safely.
The layout for each of the terminal blocks is the same so you need to wire the negative power source wire from the remaining 9v battery clip into terminal 1. The positive power source wire goes to terminal 3 with the wire to your "safe" LED going in the same terminal. The negative wire from the "safe" LED runs to terminal 2.
You should now have a functioning circuit once connecting the batteries. The way to test it is to put batteries in, turn the switch to the "on" position and press each of the buttons on the transmitter that came with the RF receiver. One channel should activate the red "armed" led and also have current running to the firing leads - get out your multimeter and see what sort of voltage you are getting - it should be between 10v and 12v and if its anything less you might have a short in your circuit.
When switched to the other channel your multimeter should show no power going to the firing leads and the green "safe" LED should light up. If this is the case then you have successfully wired it! Otherwise you might need to go back and find the source of the problem. Below is a list of common problems:
- Positive and negative wires are touching shorting the circuit
- Batteries aren't connected or are flat
- Loose connections in the circuit
- Transmitter not functioning
- Receiver not functioning
Step 3: Preparing the Enclosure and Soldering
Mark out a centreline that you will use as a reference to line the two LED's and switch up. Drill a hole big enough so the LED bezel will fit through it but the lip of the bezel stops the LED falling out. Repeat for the second LED. Drill a hole big enough for the switch to sit in. Drill two further small holes in the middle of the box for your ignition leads to come from and make a smaller hole for the RF antenna to poke out.
You will need to undo the wires connecting the LED's at this point to fit the LED's in the enclosure. Tighten the screws on both the LED's and the switch to hold them in place. Feed the ignition wires through the two centre holes so that all but about an inch of wire is exposed at the outside of the box. Feed the antenna wire through the third hole and use some electrical tape to secure it to the ignition leads. Re-connect the circuit making sure you have small strips of heat shrink placed on the wire where two wires are connected to each other. Test the circuit to ensure it works.
Solder up all the joints that need soldering and heat the shrink wrap to protect these junctions from causing short circuits.
Step 4: Finishing Touches and Testing
I used velcro to secure the AA battery holder on the internal side of the enclosure as it is slightly too tall to allow the box to be closed if its mounted upright.
Turn on the circuit making sure that the "safe" LED is illuminated. Connect your igniter leads to an e-match/igniter and switch the channel to the "armed" channel. Within a few seconds the igniter should go up in flames and if so you've succeeded, well done!
Thanks for taking the time to read, I would appreciate any suggestions for improvement!