# Linear voltage conversion and opto isolation question

Discussion in 'General Electronics Chat' started by rainyday101, Jul 14, 2010.

1. ### rainyday101 Thread Starter Member

Sep 24, 2009
50
0
I am trying to find a circuit that will take a 0-10 vdc input and convert it to 0-5vdc for my Arduino controller, and provide a linear conversion. Also I would like to provide opto isolation that is linear.

I also have a DAC (LTC1257) that I want to use to get a 0-10vdc output. If my thinking is right, I can scale the digital signal in the Arduino to get my 0-10vdc out. Again though, I would like to provide linear opto isolation from the external devices.

I have searched the internet for hours and am uncertain on how to proceed with this. (0-10 vdc converted to 0-5 vdc and linear opto isolation). Can someone point me in the right direction? I have been looking at an IL300 or HCNR200 for the opto isolation. Any help would be appreciated.

2. ### mcgyvr AAC Fanatic!

Oct 15, 2009
4,787
973
First you said 0-10VDC in and convert to 0-5V for the Arduino. Then you say you want 0-10v output.
Which one is it??
Is this for a LED/lighting dimmer circuit?

3. ### Norfindel Active Member

Mar 6, 2008
235
9
Without isolation, a simple resistive voltage divider will do. With isolation, a search throws this:

http://www.clare.com/home/pdfs.nsf/www/AN-107.pdf/\$file/AN-107.pdf
http://www.vishay.com/docs/83622/83622.pdf
http://www.ssousa.com/appnote060.asp
http://www.ece.umd.edu/~dilli/research/smartdust/power/solarcell/optocoupler300.pdf
http://electroschematics.com/4708/linear-optocoupler-circuit/

About the output, you can either search for an DAC with that voltage output, or use an opamp after the DAC.

Why do you need optical isolation? Is that connection likely to get shorted to higher voltages, or something?

4. ### rainyday101 Thread Starter Member

Sep 24, 2009
50
0
mcgyvr- It is actually a two part question. Sorry if I was not clear enough. First I am looking at bringing in a 0-10vdc input and converting that to a 0-5vdc signal so that is useable for the Arduino. Secound I am looking at outputing a digital 0-10 to a DAC to get 0-10 of an analog on this output. I would like to get linear optical isolation on both of these signals.

This is for work for an application in a manufacturing enviroment. We use 0-10vdc signals for speed signals to drives etc. We also read in 0-10vdc from a host of analog sensors. Normally I would use a PLC (programmable logic controller), but for simple applications the Arduino is a great cost effective alternative.

norfindel- Why optical isolation? External sensors in an industrial manufacturing enviroment often have longer wire runs from a piece of equipment to the control box. Damaged wires, sensors getting smashed, etc happens. Also I took apart a PLC analog input card and saw they had optical isolation, but could not get any useable numbers off of the IC.

Thanks for the links, I will be looking them over shortly.

5. ### mcgyvr AAC Fanatic!

Oct 15, 2009
4,787
973
Just my \$.02 for the output side.. I found it really easy to simply use the Arduino PWM pins 9,10,11 to output a 0-5 PWM signal then filter it to 0-5VDC analog with a resistor and cap then feed an op amp (non-inverting 2x scaling) to scale it to 0-10VDC. Looks like pretty clean 0-10VDC on my oscope...

6. ### rainyday101 Thread Starter Member

Sep 24, 2009
50
0
THANKS mcgyvr, that is exactly what I am looking for. I was hesitant to use the PWM at first. I am going to prototype a circuit and try that. The PWM is easy to opto isolate, so your solutions solves two of my problems!