swithPIC interface help please

[fozinhoffer]

I've built Eric's circuit but I can't get correct voltage across zener (-.5v). Voltage at pin 2 of db9 is -9.6 with 0 volts at base of transistor. I've tried flipping zener thinking I got it backwards.....no difference. Please help.

thanks,
mikea

[Eric Brouwer]

You did not state which of the circuits you've build. I'm assuming it's the PIC 16F84 one.

Check all your transistors, and see if their connections are correct. Also, remember that FMS must be running for the interface to function correct. When FMS is started, it will configure the supplies on the serial port.

Let me know, and we can try to help you.

[joner]

[fozinhoffer]

[Eric Brouwer]

I have build five of my PIC 16F84 interfaces again tonight, and all were tested to work correct (2 for JR, two for Hitec, and one Futaba).

Double check all your components, critical are the transistors, PIC, and zener (mounted correct). With FMS running, and pin 5 of the plug as common, you should measure around +6 to +9 volts on pin 7, and -6 to -9 volts on pin 4.

This means the supplyis fine. Next, measure across the zener, you should get around 5.6 volts. If you measure lower than 4 volts, I can suggest you changing the 470R resistor with a 220R (nothing lower), but only if you measure below 6 volts on pin 7.

The circuit should then be up and running.

Good luck.

[fozinhoffer]

Eric,
Here are my voltages with FMS running....
across pin 5 and 7 = 7.3v
across pin 5 and 4 = -5.7v
across zener = 4.77v

I still get no sign of life in calibration mode.
I will check PIC again...thanks for the help.

mikea

[Eric Brouwer]

[fozinhoffer]

[Eric Brouwer]