How do you determine the VCC, GND, and Signal on a PIR that is unmarked? Thanks.
Google it
Tried that and simply ended up with several possible lead positions. I wonder is there a way with a resistance check, for example, to pick the leads?
Look for clues.
Ground is usually connected to a large ground plane on one or on both sides of the circuit board.
VCC could be connected to a (large) buffer/bypass capacitor (electrolytic?) between VCC and ground.
And/or is also connected to the input of a voltage regulator.
You could look up the datasheets of the chips used, and see where the pins are connected to.
etc.
Post a picture of the circuit board.
Leo..
Test with a suitable supply and a 1k series resistor. the 1k series resistor on the +ve supply will avoid
damaging the thing if connected wrong, but should allow its basic functionality to be tested for each
way of connecting till you find the right one.
I've only seen two pinout variants. Unfortunately the more common pinout you find in the "maker" world's tutorials does not match the pinout of the common super cheap PIR modules but instead uses the pinout of the more expensive modules sold by Adafruit, probably only because that's the pinout of the Fritzing part.
The ones that are not marked are likely to use the cheapo pinout. They are probably marked on the other side of the PCB under the plastic diffuser dome (idiots!). Often you can just pull the dome right off because the manufacturer didn't even bother to weld down the plastic pins that hold it to the board.
The HC-SR501 PIR sensors I have DO have VCC/OUT/GND printed on the circuit board (not under the dome).
The dome can be removed in case you want to add an LDR (two holes under the dome).
The LDR stops the PIR from outputting a HIGH during daylight.
Leo..
I have a bunch of PIR modules I bought super cheap on eBay auctions. They are in multiple styles. Some of them are marked on the diffuser side of the PCB, some on the other side, as well as some other differences of board layout. They all have the same VCC/OUT/GND pinout and none of them use the GND/OUT/+5V pinout of the Adafruit and Fritzing modules
Also if you can see the PCB the ground connection can usually be traced to the groundplane on the PCB,
or buzzed-out to an obvious ground point.
But a 1k limiting resistor is usually all you need to avoid damaging stuff (at low voltage).