When I went
shopping for a real life test of the unit, I made another discovery
about PIR's. What seems to be so simple and just using a PIR with
relay output, became quite difficult. Unfortunately the common PIR's
on the market having a Line in, Line out and a common neutral. If
it's rated for 240 Volt (Europe) well, 240 volt go in and 240 volt
come out which is for our purpose not a great advantage except we
want to add a relay ourself. It's possible but would just put up the
costs of the unit unnecessary. Since a couple of days I am
experimenting with the motion sensor coming with some of the Arduino
starter kits, the HC-SR501. Advantage of this sensor is, that it runs
of our 5 V power supply and the output can go straight into the shift
register input. I also have 3 PIR's running in parallel without
blocking diodes and it works just fine.
First we need to make the connections
to the last 5 Volt and Ground bus. Then pin 1 from our PIR connects
to ground, pin 3 to the 5 Volt bus and the middle one (pin 2)
connects to the pin of our S1 which goes to the input pin (PI 1) of
the first CD4021B shift register. Since I couldn't find a fitting
diode in my electronic box, I am running 3 PIR's parallel without
any problems. But for active use as shown in the image it would
definitely be good practice to put a diode like a 1N4148 in the PIR's
output.
Again a small warning at this stage.
Please do not attempt to connect all PIR's you are planning to use to
the circuit as shown. The same goes for relays. Connect 1 for
demonstration purposes and 2 to 3 PIR's and you are fine. If you like
to connect more, please check carefully the power consumption not to
blow your Arduino board.
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