interfacing relay 8051 keil c

Posted on Feb 7, 2014

In some electronic applications we need to switch or control high voltages or high currents. In these cases we may useelectromagnetic or solid state relays. For example, it can be used to control home appliances using low power electronic circuits. Anelectromagneticrelayis a switch which is used to switch High Voltage or Current using Lowpower circuits. It magnetically isolates low power

interfacing relay 8051 keil c
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circuits from high power circuits. It is activated by energizing aelectromagnet, coil wounded on a soft iron core. For detailed working of relay please visit this page. A relay should not be directly connected to a microcontroller, it needs a driving circuit due to the following reasons. A microcontroller will not able to supply current required for the proper working of a relay. The maximum current that A89C51 microcontroller can source or sink is 15mA while a relay needs about 50 100mA current. Transistor is wired as a switch. which drives the relay. When the first pin of port P2 goes high the base current flows through the 10k resistor. This in turn switches the transistor ON. The relay gets enough current through the 12v supply to switch the secondary circuit ON.

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