Let's Make Robots!

Salvaging an old motion triggered light

The other day I found this in our local garbage dump:

2009_001.jpg

 

 

I have been trying to figure out its wiring diagram using a multimeter.

 

I know that all that is on the left is power control and everything on the right is to with the PIR sensor itself. There are 5 wires connecting the left bit to the right bit, 2 of them connected together so that makes 4.

1 of them will be V+, 1 will be G and I believe one will be to trigger the relay, what the last one would do is anybody’s guess.

 

I am wondering if I should try to get this circuit working or should I just slvage indidual parts such as the PIR sensor, 2 variable resistors, mini LDR and a bunch of resistors and caps? 

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The board on the left has the relay for controlling the light. The brown capacitor takes the place of a power transformer, (much cheaper). You'll probably find one end connects to the mains power and the other end goes to a diode. There will also be an electrolytic cap and probably a small 3-terminal regulator, (looks like transistor) to provide either 5 or 12 volts, (look at markings on regulator or relay to determine this).

 The PIR board itself should operate with + - and one lead will be the output to the relay, (through another small transistor). The two pots will be for delay and sensitivity. The better ones have a photocell, (only works when dark), and a multiposition switch for several modes, (including "walk test").

 Good luck!

Tanks for the information!

But I have decided to take it apart, the single parts are more useful to me at this stage than the entire thing. 

I can see an LDR photocell directly below the PIR sensor on the right-hand board.
You have very nice fingernails.
Thanks ;) 
Chris, I think you have been staring at Walter too long. ; j
I'm with TeleFox on just pulling it apart. However, if you want to figure out how the circuit worked as a learning experience, I'd start by identifying the most complex part, which is the IC at the top-right in your picture. Look up that chip and trace all the connections one by one between all the components and you will have a schematic.

 

I think I will go with pulling it apart, I may not learn how this circuit works but by rebuilding one myself I will hopefully learn a bit more usefully knowledge. 

But thanks for the tip, might be interesting to try it.  

I'd go for pulling it apart myself, much easier to build a circuit that does what you want it to do than to change the behaviour of an existing one.
Having said that it's probably a good idea to take a look at roughly how it's put together, that might give you some good ideas on how to use the parts.