Hi Guys - new to this forum and have a rudimentary understanding of electronics. I have considered several different ways to install a driveway sensor that's about 300 feet from the house. I don't want to use the Milton bell tubing because I'd have to take it up in winter (and it's $$), I am not keen on visible optic systems either. I looked at a giant metal detector, but then I found piezo electric coaxial cable, so I'm trying to work out the circuity with that.
I think I have it mostly figured out (probably lots of mistakes all over the place), but the main problem I'm having is that the cable generates an AC signal that I convert to DC and regulate with a LM7808, then send the signal up the driveway to the house where it triggers a BJT transistor to complete the DC circuit of the alarm bell.
The problem is, when the piezo signal is cut (i.e. I change the AC input to 0), there is still charge and voltage in the system after the wheatstone bridge which continues the input/output of the LM7808.
What am I doing wrong that the circuit won't re-open when the AC is turned off?
See attached two PDFs - one with 0V AC and one with 12V AC.
Thanks!
B
I think I have it mostly figured out (probably lots of mistakes all over the place), but the main problem I'm having is that the cable generates an AC signal that I convert to DC and regulate with a LM7808, then send the signal up the driveway to the house where it triggers a BJT transistor to complete the DC circuit of the alarm bell.
The problem is, when the piezo signal is cut (i.e. I change the AC input to 0), there is still charge and voltage in the system after the wheatstone bridge which continues the input/output of the LM7808.
What am I doing wrong that the circuit won't re-open when the AC is turned off?
See attached two PDFs - one with 0V AC and one with 12V AC.
Thanks!
B
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