Isolation

Take a look at instrumentation and difference amplifiers. Analog Devices has a pretty good website. I believe that both types of amps can give you a pretty high degree of isolation when used properly. This is especially true of the instrumentation amps, but I also think that they are usually designed with a high gain, so they may or may not work for your application.

You could still use a simple optical coupler - just calibrate against a lookup table in memory.

If the two batteries can share a common ground there's no problem.

If they have to be separated - ask yourself why you need isolation?

Just to keep the motor supply from talking to the data supply? If that's the case you can use a high impedance op amp (something like a Jfet input amp) and use relatively high series resistance into the differential inputs - it won't be "isolated" strictly speaking, but no significant current will be exchanged by the two systems, and no noise.

A cheap and dirty isolation trick is to use something like a two pole double throw relay and charge a cap with the motor voltage then switch the relay and read the voltage on the cap.

Another technique is to use a voltage to frequency converter on the motor side to send a string of pulses over to an optical coupler whose frequency is proportional to the motor voltage. You read the frequency at the micro controller and calculate the voltage or convert the pulse train back to a voltage level with a frequency to voltage converter.

--

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Flying capacitor input to the ADC: (View in Courier)

+----------->\\ DATA | \\ | | O | | | | [MOTOR BATTERY] [CAPACITOR] | | | | | O | | / | +----------->/