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Car Protection and Safety 
This remote works as well as a factory keyless remote. So I used it to wire a relay to the car starter power relay. Simply click OFF when leaving your car, and forget about anyone stealing your car, your keys or carjacking. It will not start with this device under the hood disabling your starter. Piece of Mind has never been cheaper.
Simple Modification Makes This RC Even More Versatile
Out of the box, this unit with its 2-button transmitters, works nicely to latch on a 12-Volt load with one button and latch it off with the other button. The 12 Volts for the load comes from the receiver's power supply through the relay contacts. But I needed a single-button, momentary (non-latching) unit where the relay closes only while the transmitter's button is held down, and opens when the button is released, for a garage door opener. This unit will serve with a simple modification. If you open up the receiver by removing two screws, you will find the 18-pin PT2272-L4 controller IC. Pin 12 of this IC latches high whenever the "ON" button of the transmitter is pressed, driving a transistor which drives the relay coil and closes the contacts. The high output remains on pin 12 until the "OFF" button is pressed. However, pin 17, the "VT" or "valid transmission" pin, goes high whenever either button is pressed, and stays high only while that button is pressed, which is perfect for my garage door opener. So I simply moved the base resistor for the driver transistor from pin 12 to pin 17, and now the relay closes when either button is pressed, but only while the button is pressed.
While you are in there, you can also disconnect the 12-V power supply from the relay contact if, like me, you want isolated contacts. You can cut the PC board etch around the common pin, which is located under the upper right hand corner of the relay as you look down on it from the top with the lettering upright. Solder a new wire to this common pin and run it out to your load with the existing white wire.
Another great All Electronics deal!
Handy unit - many different security codes availab
To answer the prior question about different frequencies for different units: the RF frequency stays the same, but you can program the binary code in the transmitter and receiver to provide for many different security codes. You need to open up the devices and use a soldering iron, but there are 8 inputs on the encoder chip that can be used for programming. Just match the binary pattern on each unit. I have several different units, and they all came with different codes, so you may not have to do anything.
In one application, I disabled the relay and used the TTL level output directly to a PIC for low power useage. Without the relay the receiver draws about 6 mA, most of which is the quiescent current of the internal 78L05 5-volt regulator which can be replaced with a LM2936-5.0Z for even lower standby current.
I have found the range of these units to be good - in excess of 100' in the open.
The FOBs are well constructed for the money. These are handy units for many applications
photos
I took apart a couple of these for a project and put the pictures up here : http://blog.ericmoon.net/2009/12/remote-control-lighting/
So far, range seems excellent, even with the original batteries.
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