Indoor/outdoor thermometers are handy, but the outdoor transmitter can consume too many batteries, depending on the unit. I decided to power the outdoor transmitter with an old phone charger. The voltage of the phone charger needs to be dropped about two volts to match the requirements of the transmitter. This Instructable is really about altering the voltage output of an old 5 volt switch mode phone charger to fit special power needs you might have.
I powered up the transmitter for this thermometer with some partially used AAA batteries. Notice the battery with a diagonal line through it on the upper half of the display. This is a weak battery symbol.
- Switch mode phone charger with a 5 volt, 0.5 to 1.0 amp. output
- #24 speaker wire
- 1N4001 diodes
- Brass sheet
- Electrical tape
- Dowel rod
- Staples for doorbell wire
- Mounting screw
- Soldering iron
- Heat sink
- Side cutter pliers
- Knife or wire stripper
- Wood saw
- Precision Phillips screwdrivers
- Jumper wires with alligator clips
- Hammer, etc. for mounting wire and transmitter
Step 1: Phone chargers
The output on these is typically very close to 5 volts at 0.5 amp. to 1 amp. In order to power the outdoor sender unit on my thermometer I will need to drop the voltage to about 3 volts.
Phone chargers are switch mode power supplies. I once tried to reduce the voltage on a switch mode power supply using an LM317 variable voltage regulator chip. It did not work. The power supply shut down until I removed the regulator chip.