Controller Circuit

This Switch On Time Delaycircuit has been designed to create a lamp switch operatedelectronically with an option of setting a delay in the time ofexecution of operation to reduce one or more lamps in a stairwell orany other places where this circuit may be useful. The circuit can beuseful to control various lamp or appliances that can be connected inrelay contacts.

The circuit that takes advantage of the emitter/base breakdown voltageof an ordinary bi-polar transistor. The reverse connected emitter/basejunction of a 2N3904 transistor is used as an 8 volt zener diode whichcreates a higher turn-on voltage for the Darlington connectedtransistor pair. Most any bi-polar transistor may be used, but thezener voltage will vary from about 6 to 9 volts depending on theparticular transistor used. Time delay is roughly 7 seconds using a 47Kresistor and 100uF capacitor and can be reduced by reducing the R or Cvalues. Longer delays can be obtained with a larger capacitor, thetiming resistor probably shouldn't be increased past 47K. This SwitchOn Time Delay circuit should work with most any 12 volt DC relay thathas a coil resistance of 75 ohms or more. The 10K resistor connectedacross the supply provides a discharge path for the capacitor whenpower is turned off and is not needed if the power supply already has ableeder resistor.