Help: Interfacing a Prop Sync indicator...

[RayS]

I have a nice prop sync indicator but no idea really how to interface it.

(I don't even know how it works, so unable to put together circuit to drive it.)

I was able to crack it open last night and it appears to be nothing more than 2 R/C passive circuits (No active, digital stuff going on) that could accept RPM signals from both engines. I am guessing that the disk rotates toward the engine with the higher RPM output.

Anyone on here know anything about these devices? I'd love to get your expertise if possible.

[Trevor Hale]

Hi Ray,

My trim gauge works like that.  What I would suggest is it runs on polarity.  the higher the voltage the faster it spins, and a negative voltage runs it the other way.

What I use is a simple 3904 NPN transistor through a 1k resistor.  My PWM output goes into the 1K resistor into the Transistor circuit Transistor  connected to 12V through the gauge, and to GND.   driven by PWM that will allow up to 12 volts to the gauge.

(I would test it with 5 volts to make sure you don't exceed full deflection.)

                                  12V
                                    | 
                                GAUGE   
                                    |
                                    |
                                    |                    1K
                            NPN  |-------------/\/\/\/\/-------PWM 0-5Volts
                                    |
                                   \|/
                                    |
                                    |
                                    |
                                 ------
                                  ----
                                    -