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AC Feedback using Optocoupler

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ajit5wadekar

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Hello Everyone,

I need to identify the Switch press and this switch is AC Switch so I have used optocoupler to identify the same, further I given the transistor output of optocoupler to Micro-controller through which I identify the switch press. I have attached image of the circuit so as to portray the idea.

Optocoupler Feedback.png

Now here 1st thing is that my input side of optocupler is heating cant identify the reason because the
resistor is of 200k which limits the current to 1.15mA i.e.264mW.

Also is my circuit right will the output be stable.
 

FvM

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You didn't think about the behaviour during negative voltage cycles. The optocoupler will be most likely burned by exceeding the maximum voltage rating.

There should be an antiparallel diode with the LED, cutting negative cycles. To reduce the resistor power dissipation, a high voltage rectifier diode (e.g. 1N4007) can be connected in series.

There are also special AC optocouplers with two anti-parallel LEDs that can process both input polarities.
 

ajit5wadekar

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Thank you for the help. I have added a diode for negative cycle sorry forgot to mention. Also I am planning to use the AC Optocouplers for my Application.

Can this circuit add noise to my remaining circuit, because I am using SPI Communication to communicate between Attiny2313 and CC2530 and when I send data from CC2530 there is garbage data that is coming into attiny which is acting as slave. How can I reduce this noise.

Also can you help me with the best packetization method that I can use to transfer data here.
 

Audioguru

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Will your 200k resistor breakdown when it has voltage peaks of 325V or more?
There is no filtering so the transistor will conduct with fairly low levels of noise on the AC line.
Since the opto-coupler uses the transistor as an emitter-follower then its maximum output is only +3.3V - 0.7V= +2.6V. Is this high enough?
 

ajit5wadekar

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I am getting a voltage of 3V at the transistor output which is good enough for my controller to sense.

What kind of filtering should be used?

Also as this circuit is used for identification of switch press, I think it is some how affecting my power supply. I have made my own power supply using LNK306 which in turn is affecting the controllers which cause data to lose or the controller to react in random manner.

And this happens only on switch press and works perfectly fine irrespective of that.
 

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