replacing the 6n138/139 optocoupler

[tomcody]

Hi everybody, in my country the 6n138/139 optocoupler is a little expensive and some times a hard to find component, and searching in the web I found an alternative circuit with the 4n26 or 4n36 (I tested it with both) - comes in PDIP-6 and this is the equivalent circuit for using instead of 6n138/139:

I'm not sure but if you look at the fairchild datasheet appears a lot of others optocouplers - maybe those works too.

[rasteri]

I use a 4n25, since that's the only optocoupler my local Maplin had. Never had any problems with it.

[stryd_one]

Is there meant to be a pic there?

Edit: I forgot I can see source of posts hehe the original link is:

http://img300.imageshack.us/img300/5084/circuitoconel4n26o4n36hm2.gif

I guess imagesHack is being lame with referrers...

Rasteri are you using the 4n25 as a drop-in replacement or what?

[rasteri]

Rasteri are you using the 4n25 as a drop-in replacement or what?

Unfortunately not - the pinouts completely different (for a start there's two less...) I've attached the circuit I'm using, I dunno if it's an optimal solution but it certainly works.

EDIT : My schematic was wrong, LyleHaze's is better (see below)

[lylehaze]

Your pin numbers have 4 and 6 swapped.

This might confuse somebody that tries to wire this up.

This one has them corrected.

Also, this circuit should have a pullup resistor for

pin 5 (to RX). It might work without it, but for the

price of a resistor, why take chances?

Have Fun,

LyleHaze

[tomcody]

fixed it, now are correct - I tried before a simple circuit like yours, but it doesn't works, I'll try your circuit. Thanks.

[/tilted/]

*ahem* cross post.

very useful, though.  ;D