Hi Terry, saw your deal on opto-isolators and passed the link to a friend who needs some.
You beat 20 for $4.40 with 5 for $1.00 so you topped the list.
Working voltage: 4.5V; Working current: 20mA;
And if Arduino puts out about 5.0V for a HIGH (close), the resistor needs to drop 0.5V. So:
5.0 - 4.5 = 0.5 R=E/I R= 0.5 / .02 = 25 ohms.
I get a bit antsy about the way you just did that because I used to do that for leds years ago. I'd get a usable value, just a few times higher than it should have been because I didn't take the drop across the led into consideration. I only know some basic, I have to look -everything- else up and wonder what I missed!
So I wonder, is there not much drop across the laser ... enough to make much difference? Not that I argue since HEY you've got the suckers working and very obviously know your EE stuff!
What I'm really looking for is explanation which you and others do provide so I do Thank You For That Given Already. Really... THANKS!
I guess a trim pot will carry a few mA current to let me find out working values. I might want to try resistance for 3V and 6V since I have a load of CR2032's (pretty sure they're 3V) just getting older every day now. They ran me like 25 cents each, just hate to see them go to waste. You'd pick a quarter up off the sidewalk, if it looked clean, wouldn't you? I do.
I gotta see if 2 mW is bright enough to do the 2 speakers with mirrors light show. Well, in a real dark room on a white wall it might.