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?

The specs, 3v and 0.2mA tell you what voltage is required, and how many amps it pulls. According to ye olde Ohm's Law, unless you somehow alter the resistance of your circuit (ie by short circuiting it), a 3v input to the circuit will always be pulling 0.2 milliamps from end to end. Most devices are required to list an amp rating for safety reasons; houses have fuses that carry 15 amps on average, and some big appliances that need a lot of juice might blow the fuse if used together on the same circuit.

As for your problem, if 3v is the lowest setting you have, just get the resistance rating of the device by plugging in an ohmmeter to both ends. Then match the resistance using resistors, and hook it up in series with the power supply. This doubles the circuit resistance, and since it's in series the 3v will be distributed evenly, giving you the 1.5v you need to run the device within specifications. Hope that helps (ps. not responsible if your place burns down due to shitty Mexican soldering job).