audio-sync-circuit
This repository contains EAGLE CAD files for a simple circuit that converts a synchronization pulse on an audio channel to a TTL pulse. The audio sync pulse is assumed to be the output from a sound card, which means that it's line-level and probably has some high-pass filtering applied. For example, the open-ephys-audio script plays a short click on a separate channel so neural recordings can be precisely synchronized with the stimulus. This circuit will condition the click to be a square 5V pulse so that it's more easily detected. Other recording hardware (e.g., inscopix miniscopes) can only be triggered by TTL pulses, so this circuit is necessary to synchronize playback and data acquisition. The circuitry is really just a schmitt trigger on a board with the appropriate kinds of connectors, an LED to show when the output is high, and a trim potentiometer to adjust the trigger voltage. There is a fair amount of hysteresis, so this can take some finesse to set, but it shouldn't ever need to be adjusted again.
Files
eagle.epf,line-pulse.sch,line-pulse.brd: EAGLE CAD schematics and board filesBOM-oesync.xlsx: bill of materialsschmitt.asc: an LTSpice model for the circuit- various eagle LBR files
Making the circuit
You can order printed circuit boards from OSHPark here, and the BOM has links to digi-key pages for each of the parts.