4n25/35 optocoupler detect led on/off

[StealthRT]

Hey all i am just wondering if my drawing below is correct in order to have an arduino detect an on or off led on another board using a optocoupler?

My thoughts of the above drawing is that when the led is on it will trigger the relay inside and send 5v to the arduino digital pin to read. 0v if the relay inside is not connected.

I also would possibly need to tell the arduino digital pin that its an input pullup like this:

pinMode(pin, INPUT_PULLUP);

please advise if this is correct or not.

 

[Harald Kapp]

There's no relay inside an optocoupler. In this case only a transistor (datasheet). For a typical application see figure 1 in the datasheet. You will need a pull-down resistor to generate a logic '0' in case the LED within the optocoupler is off. A pullup will not help in this scenario.

A better way of using an optocoupler is this:

Beware, this circuit is inverting: an active LED will generate a logic '0' at the output. But this can easily be handled in software on the arduino side. You can also use the internal pull-up of the arduino's microcontroller, so you don't have to provide R2.
Resistor R3 is commonly recommended to reduce sensitivity of the receiving transistor within the optocoupler to noise. A value of 1 MΩ ... 10 MΩ is suitable.
R1 is required to limit input current to the LED. The 4N25 is specified for an LED current of typically 10 mA, max. 60 mA.

 

[(*steve*)]

For the configuration as shown, you need a pulldown resistor.

 

[StealthRT]

Im looking to connect the 4n25 to a HM-10 bluetooth module led:

 

[kellys_eye]

Im looking to connect the 4n25 to a HM-10 bluetooth module led:

WHERE on the module?

 

[StealthRT]

WHERE on the module?

ummm... PIO1 (24)

 

[Harald Kapp]

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