Obviously I have too much time on my hands.
While reading some posts on Van’s Air Force about wiring up smoke pump control switches, I thought there must be a better way than most of the ideas presented. I know if I were putting smoke in my airplane (and I fully intend to do so), I’d want an ARM switch and a pushbutton on the stick or throttle. What I would NOT want is to have to keep my finger (or thumb) on that switch all the time.
So, I designed a little circuit board with an ultra simple microcontroller to act as a multi-mode switch. It does everything I want it to do…
- An indicator that uses a bi-color LED to show the ARMED / ON status
- On/off toggle action with a simple “click” of the pushbutton
- Constant ON mode while the pushbutton is held
- Sufficient to control a 10 A pump with 100% duty cycle
- Easy and intuitive to use
- Simple and inexpensive to produce
- Small and light weight, easy to mount wherever there’s space
The switching MOSFET was really the only part I was concerned about. I contacted Marvin at Smoke System Helper, who helped with testing to validate that it will drive a 7A pump constantly with no detectable rise in temperature. All the parts are rated for 10A or more, and the MOSFET has a ridiculously low Rds(on), less than 4 mOhm at the 5V gate drive voltage used. It’s rated for 160A at 30V, so it’s snoozing. The max current limit is actually imposed by the terminal block.
Overall I’m very pleased with the result. The case is not perfect — no mounting tabs — but really, the thing weighs so little that some double-sided foam tape will hold it in place, maybe with a zip tie for high vibration environments. My plan for the Celebrity is to tuck it behind the panel.