I have a small light that uses 3 AAA batteries. It has a switch, and would like to convert it to motion sensor PR.
I changed connections as below
Attached extra wire to battery negative and attached to SR505 -ve pin
Attached wire from battery positive to SR505 +ve pin
Attached SR505 - "out" to LED +ve
The light works..but much dimmer than switch on
Is there anything I can do to make it brighter like switch on ?
Hi,
Can you post a circuit diagram please.
It sounds like you are not using all 3 of the AAAs.
Do you have a DMM?
What is a SR505?
Link to specs/data?
Thanks.. Tom... 
It is of course, a PIR! I bought a few in the "old days" when they were cheaper than now. 
So it includes a 3.3 V regulator and the output is switchied with a 1k resistor in series.
Not surprisingly, the light will be dimmer than on 4.5 V. 
You can use a small MOSFET to switch the current. I would use an N-Channel MOSFET, connect the Drain to the cathode (negative side) of the LED and the Source to the negative battery terminal. The anode (positive side) of the LED goes to the positive battery terminal. The output of your motion sensor goes to the Gate of the MOSFET.
But again - it must be a true "logic-level" MOSFET which will definitely switch at 3.3 V.
The popular (and cheap) 2N7000 or more correctly the 2N7002 version may work or if more (than 100 mA as I suspect it is) current is required, perhaps an AOD4184A.
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