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relay


arsal_uet
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hi
i want to use a realay, to conrtol a bulb of 60 or 100watt using microcontroller ouput.
can anyone tel me which relay to be used keeping in view the controling parameter which wold be the dc ouput from microcontroller maximum of 5 volt and the bulb operating voltage which wold be220v ac.
thanks for ur replies.

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Hello
  It depends on the relay on how much voltage and curent you need I sometimes use electronic relays that can be triggerd by 3 volts, not sure how many Mamp's but the Pic supplies enough and the relay can handle 220V at 20amps. A driving transistor works and some will say opto's will do the job too. I guess it all depends on what parts you plan on using.
                                                  have fun
                                                  gogo 

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Simply look on the datasheet of the 8051 to see its max allowed output current and what voltage it drops down to (4V?). It is probably only 25mA and the voltage will be 4V.
Then try to find a relay with a coil that operates at only 4V and 25mA or less.
If you don't find an extremely sensistive relay then the 8051 can drive a transistor that can drive nearly any relay.

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Arsal,
You don't want to supply a voltage from the micro port to control a relay. Instead, use the micro to sink (drop) the line to 0 V.
I use the Opto 22 Solid State Relays directly off the port pin of a micro for industrial control of mains with no problems. You don't need a transistor or any other components on the control circuitry of the SSR. Just your 5 volt VCC and set a high or low on the port pin.

You can find what you need on their website at www.opto22.com
Product literature, specs and pricing are on this site, but after you figure out which one you want, search for a better price in your web browser.

Hope it helps.

MP

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