Optocoupler PC 817

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will7o20602

New Member

• May 27, 2011

• #1

Hi All ,

i'm totally new with optocoupler , so i need to use it nowadays with a microcontroller project to get a signal from the microcontroller and then control 12V contactor of a relay

Anyone can help me?

 

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Ian Rogers

User Extraordinaire

Forum Supporter

Most Helpful Member

• May 27, 2011

• #2

First you need to check the datasheet of the PC817 to see if it can drive said relay sometimes relay coils can take 100 mA+. Secondly! you need a resistor (@ 470 ohm) on RA pin.

 

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will7o20602

New Member

• May 27, 2011

• #3

i tried but it still not working. When i check there is 3.9 V on the 470 ohm resistor..

 

ericgibbs

Well-Known Member

Most Helpful Member

• May 27, 2011

• #4

will7o20602 said:

i tried but it still not working. When i check there is 3.9 V on the 470 ohm resistor..

Click to expand...

hi,
That very old type photo-coupler will not drive a relay directly, you require a drive transistor after the coupler.

EDIT:
Like this.

 

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Last edited: May 27, 2011

Boncuk

New Member

• May 28, 2011

• #5

additionally to ericgibb's I suggest to use a 6N139 optocoupler for direct connection to an MCU I/O pin.

The 6N139 transmitter requires 1.5mA only, thus keeping current requirements for I/O ports to a minimum.

Boncuk

 

Last edited: May 28, 2011