Help with rocket igniter and continuity tester

Other Hardware General Electronics
1

This is my first electronics project. I'm a professional software engineer, but electronics is new to me. Grok and ChatGPT have gotten me this far, but now I'm stuck. I need some EE learning.

My goal is to make an Arduino Giga based static fire test stand (for testing rocket motors). There will be 2 boxes that communicate wirelessly with the HC12 radio. I already have that part working.

There is a box near the test stand that we'll call the RemoteBox. It is battery powered via 12v battery, and is ruggedized to withstand unscheduled kinetic events.

There is another box 1000' away where the people are, called the LaunchBox. It's connected via USB to my laptop.

I'll be working on some experimental motors and I really don't want the ematch to go off accidentally when the RemoteBox is powered on (voltage spike, I've heard is possible?) so I thought it would be good to have a super low voltage continuity checker run off a CR2032 3.3v battery (with resistors), rather than use the 3.3v coming off the Arduino. Maybe overkill, but trying to be safe.

I would like to use 12v to fire the ematch via a relay switch when the time comes.

My current issue is getting the RemoteBox continuity checker to work when connected to the [inactive] 12v rail. I have a continuity circuit that works on it's own, but when I try to connect that circuit to the relay that fires the ematch circuit, the continuity checker stops working. I also read that I should power the relay with 5v from a buck converter as opposed to the Arduino itself, because more current than the Arduino can handle might be drawn when the relay fires (?).

This version has a functioning continuity circuit (the brown wire represents the ematch in this photo):

versionworks
versionworks1752×2132 1.07 MB

The rail that runs down the right side of the breadboard will be 12v when the relay fires. So I need the ematch on that rail. What I don't understand is how to connect the ematch to that rail and at the same time have my low voltage circuit connected to the ematch.

This is what I tried (see notes on photo about the only change from prior photo). However the continuity checking wire (green) always reads 0 volts in this version:

versionnowork
versionnowork1658×2130 856 KB

I think I might need a diode to prevent the low voltage current from the coin cell battery from being sucked into the ground plane, but I'm really not sure. I'm new to electronics.

Suggestions?

In case it matters (I don't think it does), I've also attached the Arduino code I'm using.
code.txt (2.0 KB)

2

  • The ematch can be placed in series with a low current high efficiency LED. If the LED is on, the continuity is confirmed.
    An opto coupler could be added in series for controller supervision.

  • Shorting out the LED/opto with a relay contact allows the ematch to ignite.

  • A lockout switch should be incorporated.

  • Add a 100R/220R resistor in series with the piezo speaker.

1 Like
3

Food for thought.

image
image920×543 12 KB

1 Like
4

It’s not but it is also not safe. To prevent accidental firing, the ematch should be shorted out with a relay that is normally closed (NC). That relay should only be activated when the system is armed and ready to be fired. The continuity test should be done remotely.

2 Likes
5

Safety has to be paramount.

The receiver end needs to be simple and robust. I haven't read the details, but I would want to make sure there couldn't be an accidental fire command from the fire end.

Maybe the remote person keeps control of the radio link. When working on electrical panels, there's a lock-out system as simple as every person involved having their own keyed padlock on the main isolator.