Dave

If you follow the control box schematic exactly, you’ll have a small RS273-073 piezo wired in parallel with the red “Launch” LED, which will buzz when the continuity switch is closed and the keyswitch is armed (whether or not an igniter is connected!). Not sure if you can tell from the photo, but the control box piezo is wired to the white “micro”-connector plug. (Not sure exactly how I soldered it, but it needs to be in parallel with the red LED.)

To have a buzzer at the relay box (which is pictured, but is NOT on the schematic), I think I wired the RS 273-066 in series with the continuity circuit, so that it buzzes when the igniter is connected and the continuity switch is closed. This alerts people at the pad that there’s a live igniter and, as I recall, also caused the green continuity LED on the control box to flash, since it’s all one continuous loop. I think I the resistance of the piezo was enough that I had to remove the current-limiting resistor from the green LED at the control box in order for it to work. You’ll have to test that with a multimeter. (I’m pretty sure if you wire this piezo in parallel rather than in series, the continuity current just bypasses it completely — due to the greater resistance in the piezo — and it won’t work.)

I think I ended up taking the relay box piezo off because it got too annoying, I don’t recall. My advice: try wiring everything up just like in the schematics, then experiment as necessary if you need more warning sounds. (Also, you might consider using a different [read: polycarbonate] enclosure for the relay box — I had lots of trouble insulating the connector posts from the metal box.) Hope that helps!