Detect AC Power supply

[steve_venkat]

This is the circuit I' using to detect the AC voltage.I can't get any output from this circuit..
Is simply in Idle.Their is no negative voltage is detected.

 

[Alec_t]

You can't get a negative voltage out, since the '814 output transistor is only connected to a +5V supply.
What AC voltage are you trying to detect? 110V mains?

 

[kellys_eye]

With 100k resistors I'm surprised you're getting anything at all. This means only 0.5mA through the opto's LEDs. Without referring to the data sheet (coz I can't be bothered to download one) is <1mA sufficient to activate the LEDs?

 

[steve_venkat]

You can't get a negative voltage out, since the '814 output transistor is only connected to a +5V supply.
What AC voltage are you trying to detect? 110V mains?

Its connected to MCU input,The resistor is connected as pull-up resistor...
Have to detect 230VAC,But the voltage will vary from 160VAC to 280VAC...

 

[steve_venkat]

With 100k resistors I'm surprised you're getting anything at all. This means only 0.5mA through the opto's LEDs. Without referring to the data sheet (coz I can't be bothered to download one) is <1mA sufficient to activate the LEDs?

Its 5mA current required.?If the voltage is constant(230VAC) means 4.k OHM is enough for it..?
But the voltage will vary from 160VAC to 280VAC...
At this point how to choose the resistor value..?

 

[kellys_eye]

The current range for LED operation can vary considerably yet still allow it to work. Take the average AC voltage (220V) and use that to calculate the required resistor for 5mA current flow. Any changes either side of that will be acceptable.

Alternatively take the 230V as the 'working value' and choose a resistor for that.

 

[Bluejets]

One of these and stick an opto, relay or whatever on the end. Cheap enough and will cover the range of your input voltages no worries.
https://www.ebay.com.au/itm/AC-DC-1...=item3b1f6c79bb:g:gRwAAOSwtMNbuB9~:rk:21:pf:0

 

[steve_venkat]

The

Its 5mA current required.?If the voltage is constant(230VAC) means 4.k OHM is enough for it..?
But the voltage will vary from 160VAC to 280VAC...
At this point how to choose the resistor value..?

The LED in optocoupler is 20mA current and 70mW power dissipate.So I calculate resistor value for 5 different range of input supply and took average value from that.Its 11.1K,2W...Is this Correct method or have to change something..?

 

[steve_venkat]

The optocoupler working fine with ground supply...I tried with positive voltage instead of ground supply and connected the output from the optocoupler to controller.Their is no response in the controller.Is this circuit is correct..?

 

[(*steve*)]

On the optocoupler side, I would make the 1k resistor 10k, and connect it from the emitter to ground. The emitter should be connected to the microcontroller input pin.