1st Draft TODOs

## Core Design Features
- < 1ms lick detection latency
- no false positives
- Ephys-invisible

## Core Board Features
- [x] RP2040 + 16MB ram
- [x] Isolated full speed USB
- [x] Harp synchronizer input
- [x] SWD input
- [x] serial debug port input
- [x] dual analog and digital power supply (analog front end and digital circuitry)
- [x] dual analog power supply for opamps
- [x] 100KHz clean sine wave generation
- [x] single lick detection input
- [x] 60Hz noise rejection
- [ ] solenoid noise rejection with low-voltage-triggering TVS diodes

## Bringup
### Harp Core PCB
- [x] Bringup Harp Core on a PCB
- [x] Confirm active shielding stage works
- [x] Confirm bandpass filtering stage works

## Considerations
- [x] investigate if we need active guarding on first opamp input.

## Docs
- [x] choose the right license(s)
- [ ] cable/hookup specs for lick spout
- [ ] document design (schematic + design choices)
- [ ] document lick tube cable

## Testing
- [x] Test USB Isolator with Adafruit [ADUM4160 breakout](https://www.adafruit.com/product/2107). Ensure no additional latency has been introduced.
- [x] Test final breadboarded analog front-end design with a probed mouse