Sequential touch switch

The touch switch is based on a Schmitt trigger with hold contact, which is built from IC(1a), IC(1b) and R3. The output of IC(1b) is fed back to IC(1a) via R3 resulting in both gates maintaining their stable status. As long as the circuit is quiescent, that is, the anode of D(1), is low and the cathode of D(2) is high, this situation continues.