Recent content by alan

Hi All, I tried the circuit from my post #13 and it appears to work ok, though PWM values between 1 and ~90 have the same on/off times. Anyway, I built up 3 separate circuits for 3 LD's but i noticed that the R4 sense resistance required to get a particular current value (200 mA) varied a lot...

Hey all, I've been messing about with the 2-opto circuit from my last post but it doesn't work very well. When The arduino is off and optos 'open'... the laser is on... which I was trying to avoid with the second opto! I think maybe its because the fet gate is floating in this setup. So I've...

Bobhaha, thanks for that. I guessed there might be but I'll try the diy route for a wee while first ;) HIMNL9, thanks for your suggestions. The common positive sounds good but I was thinking that if the arduino is not plugged in (and the LD is) then the LD would be on. So I've been messing with...

Ok, thanks for that HIMNL9, I'll give that a go. Common positive: I need to connect arduino PWM to optocoupler anode (thru a resistor) and arduino ground to optocoupler cathode (no need to connect arduino 5V anywhere). Is this correct? Thanks, Alan.

Hi HIMNL9, Ok, I think I see what you are saying, its left sortof floating. So actually if I ignore the two circuits that I posted and connect the arduino directly to the circuit that Bionic-Badger posted I should be probably ok (assuming my calculations are ok above!)? Q1 is tied to ground...

Thanks for all the replies. Bionic-Badger, I've been looking at that instructables circuit you linked to and I have a real newbie question for anyone with patience/time.... If I have 5V VCC, a 2.2V LD operating voltage and a 0.28A operating current.... is the following correct? R3 =...

Hey all, I've been lurking for a few weeks but this is my first post so go easy on me :) I'd like to use an Arduino (uno) and an optocoupler to TTL/PWM switch a ir LD (808 nm, 280 mA) which gets a constant current from an LM317. From my lurking here (thanks folks for all the excellent info)...