look at pin 21

 

Disregard what I said about the led, I am stupid.

OK I'm getting confused, lets go back to the start, I have been told I could use the H11AA1 but don't have access to it. I now have access to the SFH620A-1, SFH620A-2 or SFH620A-3. 3 Questions:

1. Are these usable?
2. If so which one is best this (I am in the UK if that helps)?
3 And what resistors do I use?

My answers from my silly head:
1. Yes
2. Doesn't matter
3. 2X 47K Resistors 1/2W in parallel or similar.

 

Hello,

All three are suitable.
The transfergain is different, I would choose a -2 or -3 version.

Greetings,
Bertus

 

Would you mind explaining transfer gain?

 

Hello,

I have taken a sharper look at the datasheet, it is called Tranfer Ratio.

It is the ratio between the Led and transistor current.

Greetings,
Bertus

 

So what will that effect? If I have UK mains(take away some cos the 2X 47K Resistors 1/2W in parallel) going into the Leds, what current will be coming out?

 

Hello,

The led current is about 10 mA.
That depends on the value of the collector-resistor.
If it is 10K and the powersupply is 5 Volts , it will be round 5 mA.
If the ratio is higher the edges of the pulses will be sharper.

Greetings,
Bertus

 

I'm using an Arduino so it will be 5V and where do I find out the value of the collector-resistor.

 

Hello,

You posted a link yourself where a 10K resistor is used.

I cutted this from your post. Only you will use the SFH620.

Greetings,
Bertus

 

But im not converting the AC to DC, Im just using the SFH620A-2 straight away????

 

Hello,

You are rectifying but not smoothing the signal.
You will get a pulse at every zero-crossing.
So the frequency of the pulses is double the input.

Greetings,
Bertus

 

No, Im not using the rectifier, Im using an ac input chip so I dont have to.

 

I think Im correct in saying that?

So, like this:

 

I think Im correct in saying that?

No. Bertus is right. Look at the IC input. http://www.isocom.com/SFH620A-2/AC+Input.htm. It has a pair of back to back LEDs. Each conducts on alternate half cycles...think rectifier. The output transistor doesn't care about the polarity that makes each LED conduct. It will conduct as pulsating DC with twice the frequency of the input AC signal. The output will look exactly like full-wave rectification, which it essentially is.

Ken

 

OHHHHH I wasn't thinking again. and in your opinion, what should I use? SFH620A-1, SFH620A-2 or SFH620A-3.

 

Hello,

Now I see it, the SFH has two leds back to back.
(there are optocouplers with a reverse voltage protection diode in it).
Then you do not need to rectify.

As I said before I would go for the -2 or -3 version.
(these will give sharper edges on the output pulses).

Greetings,
Bertus

 

so -3 will have sharper corners on the signal than 1 or 2? if so thats better for the microcontroller, right?

 

Hello,

Yes , you are correct.
Just try it.
If the pulses are not sharp enough you can lead them through a schmit-trigger, like a 74hct14.

Greetings,
Bertus

 

Ok I will try that the second the parts arrive and post back with results.