A 16 bit DAC solution for your Arduino! The schematic is very simple, it's just the DAC (Analog Devices AD420), a few capacitors and an operational amplifier used as voltage follower in order to provide some buffering to the DAC output. The DAC is not very cheap (around 15-18$!) but it allows to obtain a good resolution in order to satisfy all your accuracy needs... I've built the circuit using a smd-to-dil pcb adapter, but the DAC is also available in a breadboard-friendly PDIP package.