The specs of this project are:

• 1 input channel: IR 38kHz receiver
• 2 output channels
•  2 different frequency pulses in the 130 Hz range
• Programmable constant current on output in 30 - 250 uA range
• LED to show pulsing (2 different patterns or colors)
• LED to show power on
• IR transmitter (off-the-shelf) compatible with 38kHz receiver
• Coin cell battery CR1025 (10 mm dia)
• Desired weight < 2.5 grams
• Desired area footprint 1 cm x 1 cm

I'm prototyping with one of Microchip's Curiosity dev board, which comes with a 20 pin DIP PIC16F1619.

I've gotten to blinky with MP Lab X and the code configurator, the documentation isn't that great, but maybe just because there's a lot of it. Getting to blinky took 2 hours.

I swapped the 20 pin DIP out for a 14 pin DIP PIC16LF1703. This chip has 2 on-chip opAmps. I need a constant current supply for the circuit I'm designing, and so thought it might work with one of the on-chip opAmps. 

VOLTAGE TO CURRENT CONVERTER