d. Light operated switch
Description of remote operated switch
When you press an infrared transmitter or normal TV remote control near TSOP1738 infrared sensor, the 555 timer configured in monostable mode gets triggered. The output pin 3 of 555 timer remains on for a while and the ‘on time’ is determined by the resistor R2 and capacitor C1. The output at pin3 along with transistor BD139 activates the 6Vrelay. The relay switches on the 555 timer configured in toggle switch mode and that finally glows LED D2. When you press remote control again near TSOP1738, the LED D2 switches off. Fig. Remote operated switch(Click on the schematic to enlarge it)
This project was tested and verified during LDR Engineering Course.