I like knowing when the temperature near the road surface starts to get near freezing, so I bought a thermometer
It turns out that it wants 5V in, not 12V, so I hooked up a voltage regulator (LM7805, a whopping $1.59 at Radioshack) and for good measure added some capacitors to filter the signal. Adding the capacitors might be overdoing it, so then you only need the dinky little 7805.
Here is what I conjured up:
After that picture was taken, I put electrical tape around each separate leg of the 7805 to prevent short circuits and I bolted 2 pieces of scrap aluminum to the top to function as a heatsink. The 7805 dissipates the energy from the voltage drop as heat.
Don't know if the heatsink is needed either, but I thought it is easier to do now than have to add it later. I even put some Arctic Silver in between the plates, that I had left over from a CPU install a year ago.
I will post pics again after I install the thermometer in my dash.
As you can see it reads in Celsius, but since I was born and raised in the Netherlands I am quite comfortable reading that. Moreover, you simply need to start paying attention when the number drops near 0.
You can tell it is not very warm in my garage.