Can someone please reccommend me an opto-isolator?

I need to optically isolate my arduino INPUT from another system. The other system is 1000VDC going through a voltage divider (1.5Mohm pot) to output 2.5V (adjustable, I could increase this, but I was using 2.5V to light an LED). Right now I am using a red 3mm LED and a photoresistor inside shrink tubing as an opto-isolator, which works alright (mostly), but I want it to look professional. the current available for the switching power is very low (the LED draws .5ma, and I would like the opto-isolator to draw less than that if possible). I think this is backwards from the way you would normally use an optoislator, but I need it to switch my 5v from arduino to input. Thanks!

I think that is going to be a hard find. Most opto-isolators use a led for input and require say 3ma minimum. I'm suprized your setup works at .5ma. Maybe some kind of isolation based on a neon lamp would work better for your high voltage sensing?

Good luck

Lefty

If you want to keep the current drawn from the 1000v circuit low, you will need to make a voltage divider with several dozen Mohms and feed the voltage into an op-amp with a high input impedance. As retrolefty says, the current requirements for an LED are higher than you say you can tolerate.

Here we have yet another application for an isolation amplifier.

What about this one? http://www.newark.com/avago-technologies/hcpl-4731-000e/optocoupler-darlington-3750vrms/dp/31K7040 do you think it would work for what I need?:
Recommended Operating Conditions

Parameter Symbol Min. Max. Units

Power Supply Voltage V CC *

1.6

18

V

Forward Input Current (ON) I F(ON)
40
5000

µA

Forward Input Voltage (OFF) V F(OFF)


0


0.8


V

If you can afford 50 microamps of current to be drawn off your 1KV circuit, then this jobby looks like doing the job. That's 50mw of power.

What about this one? http://www.newark.com/avago-technologies/hcpl-4731-000e/optocoupler-darlington-3... do you think it would work for what I need?:

I've used it (or one of its relatives) ten years ago and it's good enough. The only draw-back of your design is that you may need high voltage and high power resistors for your voltage divider:

I did it with two resistors in series without voltage divider. Both resistors had enough resistance for opto's IF current. Then remember to consider isolation big enough (>500 V) for both and its power.

Good Luck,

/me

I've used it (or one of its relatives) ten years ago and it's good enough.

Oh, excellent. do you think it would also work as a relay driver for my arduino OUTPUTS?

The only draw-back of your design is that you may need high voltage and high power resistors for your voltage divider:

Got 'em

I did it with two resistors in series without voltage divider. Both resistors had enough resistance for opto's IF current.

So you're saying that if I had a hig value, high power rating resistor, the 1.4V forward voltage would be dropped across the LED inside, and the other 998.6V would be dropped across the resistor, no divider necessary?

Then remember to consider isolation big enough (>500 V) for both and its power.

are you referring to the isolation rating of the optocoupler itself? or as to the physical layout of my circuit and not running HV and LV wires too close. Thanks!

So you're saying that if I had a hig value, high power rating resistor, the 1.4V forward voltage would be dropped across the LED inside, and the other 998.6V would be dropped across the resistor, no divider necessary?

Thats correct.

Then remember to consider isolation big enough (>500 V) for both and its power.

This means that electrical isolation between resistor terminals must be greater than 500 V in order to achieve 1000 V with two resistors. Of course, your opto-isolator is able to achieve 1000 V between the high voltage side and the logic side.

/me