Surprisingly that worked. With a normal diode, not a zener. Used the forward voltage of the diode to drop the Li-Ion voltage down to the voltage the radio works at. No voltage regulators needed now, and the DS18B20 temp sensor will work at all the voltages. I'll just have to be careful not to short circuit anything and blow up any batteries.
Do you need to be careful with Li-Ion batteries not discharging fully?
Yes, looks like it. Just looking it up and they shouldn't be discharged to under 2.4V. All the cells in the laptop battery are 2.2-2.3V so maybe I shouldn't be using them. The one I charged didn't explode though.
Do you have a 18650 battery charger?
Yes, just got one for my bike lights.
My !!/really exciting/!! Atmega 328p programming board.
It's got the 16MHz crystal and caps so I can program my chips to run at 8MHz off the internal clock before sticking them in my temp sensors (only have 1 so far though).
Forgot to upload the picture.
I've got a couple of 328ps but couldn't get them to work. Need to try again.
They're pretty easy to get working. Everything on that board will get it detected by AVRdude. You do need a USBasp to program it or upload a bootloader if it doesn't come with one.
But it should have have some caps and resistors and other bits to properly connect it all up.