EMI on Long Lick Cable (Triax)

[Poofjunior]

This has long been an issue with all lick detectors, and it's fundamentally a hard problem to solve.

To detect licks while not being detectable on ephys recording in the mouse brain, we need to introduce and detect a relatively small signal. Currently, this signal has a 100KOhm series impedance and plays a 100KHz waveform. By running this cable down a long wire, the high impedance nature of the signal makes the signal very susceptible to external noise. (This is after shielding and guarding measures have been taken.)

The current solution (shielded and guarded triax) cable works well in some rigs and poorly in others, depending on what other EMI sources are present. A better solution would be to update the design to remove the need to run a high impedance signal over a long cable.

One solution is to split the board design into two boards:

1. a small board that solely buffers the signal (converts low impedance to high impedance)
2. a "main board" that does the rest of the downstream processing.

This solution removes the need to use a triax cable altogether. Since the resulting signal sent to the main board is low impedance, a variety of multiconductor shielded cables can be made to pass this signal.

[Poofjunior]

Current progress on the cable buffer board:

The current board is 25 mm long and accepts an M3 screw for attaching to the lick tube, and a JST SH cable.

Current progress on the main board:

The main board simply removes the triax cable and first buffer. All other features of the signal chain are unchanged.