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RC Lost Model Alarm Modification

K

Kevin Walton

Jan 1, 1970
0
Hi

I have purchased a Lost Model Alarm with a circuit that looks like
this:

http://mach.unseen.org/~kevin/electronics/lma/lma1.gif

IC1 is a PIC 12C508A, TR1 is a transistor marked 2N02, C1 is I assume
a supply decoupling capacitor.

The PIC is powered from the Remote Control Reciever battery.
switiching on the alarm if no signel is recieved at connection point
S.

This circuit has a design problem, even though it has it's own
integral battery if the reciever battery is not connected then the
alarm wont sound. I would like to solve this by powering the circuit
from the internal 12v battery. So, whenever a singlan is not present
at S the alarm will sound.

I atempted this like so:

http://mach.unseen.org/~kevin/electronics/lma/lma2.gif

IC2 is a 78L05, 5V regulator, in theory taking 12V and producing 5v.

However this circuit now just alway provides a small voltage to the
alarm continuously and the presence of signal at the input makes no
difference.

I am obviously missing a fatal problem, can someone point it out and
possibly explain a way around the problem for me please?

Thanks
Kev

kevin at unseen dot org
 
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