hi,
any one may help to modify or convert a device from using 2 units of AAA battery to using car battery??
the device have output(LED), sensor(the sensor together with battery tray)...

how can i modify it?and adapter needed??

thanks..

 

2 x AAA nominally 3v but up to 3.5v ...you need a voltage regulator chip ..a variable one set with resistors should just get you down to 3.5v as the fixed ones go to 5v though you could use 5v regualator and a couple of series diodes to drop the volts to 3.5v

 

This might work:

http://www.futurlec.com/Linear/LM2937ET-3pr.shtml

These are nice because they are internally protected from the harshness of an auto's electrical system. This one provides 3.3v @ 500ma, I hope that's close enough. Their only requirement is to use a high quality capacitor (low ESR) on the regulator's output pin.

If you need exactly 3.0v, you'll need an LM317 which is an adjustable regulator. These are not directly suited for automotive use and will require external protection.

All of this could be put into a little box and plugged into the cigar lighter so there would be no need to disturb the original auto wiring (which is forbidden here).

 

hi all,
thanks for replying, can show me the circuit diagram?because i not from e & e background..
thanks a lot..

 

Look at the datasheet for the 2937, it has a typical application. That will work, use a small fuse between the +12v input and the 2937. Mount the 2 capacitors close to the regulator.