Touch Switch Circuit
Posted on Jan 11, 2013 11825
When the touch-on contacts are bridged, pin 6 of Ul-b goes low, which forces its output (the set output) at pin 4 to go high. That high divides along two paths; in one path, the output is applied to pin 2 of Ul-a, which causes its output at pin 3 to go low. That low is, in turn, applied to pin 5 of Ul-b, which latches the gate in a high output state. In the other path, the output of Ul-b is used to drive Ql. When Ql turns on, U2`s internal LED lights, which turns on its internal, light-sensitive, triac-driver (diac) output element.
The triac driver feeds gate current to TR1, causing it to turn on, and light the lamp (11). When the off contact is bridged, IJl-a`s output switches and latches high, causing Ul-b`s output to go low, turning off the lamp.