Catch exception on aref check during connect

This was preventing a clean connection on older firmware which
prevented auto-updating.
Revert to previous API for avr_helpers until...

Revert to previous API for avr_helpers until this bug is
fixed:

https://github.com/wheeler-microfluidics/avr_helpers/issues/1
Allow a 1% tolerance on waveform frequency to...

Allow a 1% tolerance on waveform frequency to prevent exceptions caused by
floating point errors.