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Here is a light-operated, remote-controlled solidstate switch to operate a lamp. During darkness, the resistance of LDR shoots up to meg-ohm range. Thus, the triac does not get gate drive and hence it does not conduct. Circuit diagram: Light-Operated Light Switch Circuit Diagram When LDR is illuminated by means of a torch-light beam, the resistance of LDR suddenly decreases (below 10-kilo-ohm). This causes the triac to conduct and switch  ‘on’ the lamp. Light received from the lamp (not from the torch) keeps LDR’s resistance low. So, the lamp re-mains continuously ‘on’. Once the lamp is‘on’, it can be switched  ‘off’ again by in-terrupting the light falling on LDR, by either waving hand in front of it or by interrupting power supply to the circuit for a moment. RFC emplo-yed here can be made by winding about 15 turns of 18 SWG wire over an insulated ferrite rod. Author : Pradeep G.  - Copyright :electronicsforu

Here is a remote operated spy robot circuit which can be controlled by using a wireless remote controller. It can capture audio and video information’s from the surroundings and can be sent to a remote station through RF signals. The maximum range is 125 meters. It overcomes the limited range of infrared remote controllers. This robot consists of mainly two sections. They are explained in detail below. Remote Control Operated Spy Robot Circuit – Block Diagram Remote Control Operated Spy Robot Circuit - Block Diagram 1. Remote Control Section The circuit uses HT 12E, HT 12D encoder and decoder. 433MHz ASK transmitter and receiver is used for the remote control. H-bridge circuits are used for driving motors. Two 12V DC/100RPM gear motors are used as drivers. The working of the circuit is as follows. When we are pressing any key in remote controller the HT 12E generate 8 bit address and 4 bit data .The DIP switches are used for setting the address. Then the ASK transmitter sends the 8 bi

This solid state DC switch can be assembled using just three transistors and some passive components. It can be used to switch on one gadget while switching off the second gadget with momentary operation of switch. To reverse the operation, you just have to momentarily depress another switch. The circuit operates over 6V-15V DC supply voltage. It uses positive feedback from transistor T2 to transistor T1 to keep this transistor pair in latched state (on/ off), while the state of the third transistor stage is the complement of transistor T2’s conduction state. Initially when switch S3 is closed, both transistors T1 and T2 are off, as no forward bias is available to these, while the base of transistor T3 is effectively grounded via resistors R8 and R6 (shunted by the load of the first gadget). As a result, transistor T3 is forward biased and gadget 2 gets the supply. This is indicated by glowing of LED2. Circuit diagram : Solid-State Switch For Dc-Operated Gadgets Circuit Diagram