Conclusion

I hope you find the model rocket ignition system schematics useful, even if you don’t build my exact board. Although I encourage you to include a programmed microcontroller for safety features, you can still get the power benefits of locating the battery near the launchpad from even a brainless home-etched version of this project.

Video

Here is a brief example of the rocket ignition system being shown off:

Potential Improvements

The new device is better than my original fancy rocket launch controller. However, now that I have built and used it, here are some changes I will keep in the mind for the next revision.

1. A current-limiting resistor (say 1 kilohm) could be added between IC1 and the Go pin to limit current if someone uses both the microcontroller and a button connected directly to Go. That would be an unusual setup, and IC1 can handle the shorted pin, but nevertheless an added resistor would make the solution more robust.
2. A diode between the interlock output and everything but the relay coil would allow the interlock switch to be single pole. This might save some money and provide a wider variety of choices of keyed switches.
3. An optocoupler could be placed before the launch and arm switch inputs to provide circuit isolation and input protection.
4. A double ring socket (TRRS) instead of a single ring (TRS) would allow the remote control to draw power.
5. The circuit board and igniter connections share a power source, which can reset the microcontroller during launch if the battery voltage drops too much. By adding an additional connection and a diode after D1, a spare battery (say a 9V) can provide backup to the circuit board.
6. The quantity of LEDs and blink states can be somewhat confusing. A microcontroller with more pins could support an LCD for better information. This would be a significant change.

Suggestions?

I would love hearing from you if you implement your own version of this relay-based model rocket ignition system. Or, even if you just have comments, questions, and ideas for improvements.

Update: This rocket launcher has been revised!