Hi, I'm done with my PIC based stereo control, remote start, car alarm.
Everything works wonderful, BUT the project is crippled beyond use due to
electrical noise causing the Holtek HT12D decoder to reset which produces a
false VT (valid transmission) and resets the data latches to 1111b. This
happens to be the data nibble which causes the alarm to arm/disarm. I realize
the encoder/decoder pair isn't the most secure thing I could use, but this
really doesn't help. It intermitently happens when I roll the windows up/down
(electric) or lock/unlock the doors. Using the alarms onboard lock/unlock
function doesn't seem to cause the same problem at all even though the relays
to do this are the same PC board. I'm using a 2200uF across the input, 7805
voltage reg., decoupled every chip onboard with .1uF caps across the leads,
and  used a huge ground plane. Still doesn't fix it. None of the other chips
(PIC16F84, 74HT166 to increase input pins, JRC 1to16 shift reg to increase
output pins) are affected at all. I've studied the output of the RF module
and have found nothing strange. Just a narrow pulse here and there (when not
transmitting) . I've tried 2 different brands fo RF modules also. I've
disconnected everything but the power but still the problem persist. Any
ideas? Thank you much.
Matt B.