[phyrrus9]

What circuits do you want me to build with the leftovers?

Knowing you, you'd probably build a nuclear power plant.

On a serious note, what can they actually be used to build?

I actually do want to build a low scale nuclear power plant (like the size of a 5 gallon bucket), but thats gonna take a lot more research and learning before i go anywhere near the materials for that.

As for this, I'm using it to make a hybrid analog-digital circuit to drive a 2-speed fan for my car's radiator. Basically I'm using an NTC thermistor taped to the lower radiator hose. As temperature increases the resistance across it will decrease, allowing more of the current to flow through it. I'm adding resistors before the NTC so that I can tune the level of current flowing there so that the voltage right before the NTC will be exactly 1.5v at the temperature I want. Before the NTC I've got a p-MOSFET (turns on when input is off, aka below 1.5v). So when the thermistor gets hot enough, the p-MOSFET input will be driven low causing the output to be high and supply power to a relay that will switch from low to high speed on the fan. As it cools back down the transistor will turn back off and if everything goes right it will cycle back and forth at 65-70C