First check that DIO1 mode is configured properly. In the configure system window of the 220A olfactometer control software, ‘sequence start trig’ should be selected. If so, then the problem is likely from the sequencer window where the user must check the box ‘use DIO1 as sequence start trigger.’ For control of individual odorant release within a sequence, the user must select ‘ext trig’ as the delay to challenge to trigger each line of the sequence externally. In addition, you wish for the odorant duration to also be externally controlled, the user should select ‘falling edge’ which indicates the final valve will be closed when the unit sees the falling edge of a TTL pulse.
external triggering of the final valve (release of odorant to animal) can be done directly using the front panel BNC connection labelled “Final Valve Trg In.”