120V to 1.5V

Hi, I recently bought a remote thermometer but it all runs off of watch batteries and I don't want to have to keep replacing them whenever it dies. I was wondering if there is anyway I could take the 120V from my house and convert it down to 1.5v then permenently wire the remote temperature sensor to the house power. I am not totaly in the dark, could I use a plug transformer and get it down to 3V and then use a resistor to kill the rest?

If you're at radioshack, get a 3.3v zener diode. This will be your "clamp". Get a simple NPN transistor too (2n2222 or 2n3904). grab a 10uF capacitor, and a few 1k resistors. Also get a small potentiometer (10kohm). The use of an LM317 requires a few volts (~2) above the output rail, so it becomes a problem. The BJT will drop ~0.7v from base to emitter too. tie your BJT's collector to the +v supply voltage. Tie 2 1k resistors (in parallel) from +v voltage to the cathode of the 3.3v zener. Tie the anode of the zener to ground. Tie the 10uF capacitor in parallel to the zener diode. This gives you some supply stability and transient regulation. Now, tie the pot to the cathode node of the zener diode and the other end to ground. Tie the wiper to the base of the BJT. The output will be tunable from ~0v to 2.6v. Tie another 1k resistor to ground from the emitter in a temporary manner as its your test load. Measure the output voltage on the emitter and tune the pot until it reads 1.5v, or whatever you need. This will act as a pretty good voltage source and can source a few mA.