Device Resets / erratic operation - 16F88

[Archangel]

The NPN - PNP connection allows the PIC to switch +12V on the high side, to keep the power to the circuit on, after the power path from ignition switched 12V throuth the indicator lamp is no longer available. I use the signal through the light bulb to tell it when the ignition is turned ON, as well as being able to ground the lightbulb and cause it to illuminate.

I used a Bosch relay on a 71 chevy to power an HEI ignition and the relay would hold down to 3volts which was low enough to allow engine to run when switched off due to receiving power through the alternator light, had to kill engine in reverse gear, where the backup lights would load it enough to cutoff relay.

[turbokinetic]

I used a Bosch relay on a 71 chevy to power an HEI ignition and the relay would hold down to 3volts which was low enough to allow engine to run when switched off due to receiving power through the alternator light, had to kill engine in reverse gear, where the backup lights would load it enough to cutoff relay.

LOL! I had the exact same thing happen on my 72 Nova. When I converted it to EFI, the ECM, ignition, and everything else was powered by a relay that wouldn't drop out until the alternator was unplugged. Fixed that by installing a diode in the alternator warning lamp wire.

It was kind of nerve-wracking because the engine was a newly rebuilt one I had put together, and wired everything up. The first time I turned the key, it started instantly, and the transmission started spewing oil profusely from a forgotten cooler line, and I couldn't shut it off!!!!

David

[turbokinetic]

Well - after all the fuss and mess; the real cause was after all..... a bad resistor. I had intended to use 1K resistors for the the transistor bias resistors on the relay, valve, and lamp driver circuits. They did all come from the same package.

The resistor for the relay driver was a 1R (1 ohm) resistor instead of 1K (1000 ohms) and was badly overloading the output on the PIC, causing it to malfunction. I finally determined there was a serious issue when I felt the PIC chip, and the 5V regulator both getting VERY WARM when the relay output was active.

After changing the resistor, the circuit works fine, without any extra choke coils or capacitors, and nothing gets warm.

The resistor was correctly marked as a 1R resistor (by color bands) but was in a package with 1K resistors so (like a dummy) I did not look closely at it before soldering it in.

Live and learn. Thanks again for the ideas, I really appreciate it and am glad to have found a place to discuss these projects!

Later,
David