Position: Index > Switch Circuit >

Phone Activated Solid State Relay Switch Circuit

2015-09-19 03:10  
Declaration:We aim to transmit more information by carrying articles . We will delete it soon, if we are involved in the problems of article content ,copyright or other problems.

"solid-state" relays, which use an SCR , TRIAC, or transistor output instead of mechanical contacts toswitchthe controlled power. The output device (SCR, TRIAC, or transistor) is optically-coupled to an LED light source inside the relay. The relay is turned on by energizing this LED, usually with low-voltage DC power. This optical isolation between input to output rivals the best that electromechanical relays can offer.Each and every time a phone on the same line or calling numberis taken off-hook, the circuit will be activated to control an external electronic circuit. If several extension telephones are used on one phone line, the circuit can be useful as a busy indicator. LEDl contains a special flashing red  LED  that makes an excellent indicator for a busy circuit condition. The solid-state switch can be used for several other phone-activated applications, such as automati cally turning on a cassette recorder, starting a phone-use timer or counter, etc.A small relay can be connected at points A and B, in place of LEDl, to control external circuits. A 117-Vac-to-6-Vdc plug-in power supply can be substituted for the battery to keep the operating cost at a minimum. The 48-Vdc, on-hook, phone-line voltage keeps Ql in the cut-off condition, allowing no current to flow through resistor R4, hence Q2 remains off. Resistors Rl and R2 keep the solid-state switch circuit from causing any problems with the telephone`s central-office equipment. A solid-state electronic switching device which switches power to the load circuitry, and some coupling mechanism to enable the control signal to activate this switch without mechanical parts. The relay may be designed to switch either AC or DC to the load. It serves the same function as an electromechanical relay, but has no moving parts.