I can supply outline circuit diagrams for the following if desired and some references but will start with a word outline as others may have better suggestion. If the floating signal is not "isolated" per se and only floats within the power supply range of a standard op-amp (say about +-15 volts ) then a standard 2 input differential amplifier will give you the ground referenced result with as little as 1 op-amp (3 for a full instrumentation amplifier). If the floating voltage floats at much higher voltages or true isolation is needed then "telemetry" style approaches may be needed. Two of many approaches are: 1. Siemens (and others) make opto couplers which have 2 receivers so that one can be wired in a feedback loop and allow a linear voltage to be transmitted across the opto. Siemens IL300-X016 - RS sell for $NZ11.54 in ones. Farnell probably also sell them. 2. A "reasonable" method is a voltage to frequency converter and use of an opto isolator to send the pulses to the PIC for counting. Could be a 555! or a purpose built IC such as LM331 (Nat Semi) , TC9402C (Burr Brown) AD654 and others (RS 1998 catalog page 1-1133) As you are a "local" (to me anyway :-) you could ring me on (09)8372999 if any of this sounds useful. -----Original Message----- From: Gavin Jackson To: PICLIST@MITVMA.MIT.EDU Date: Sunday, 26 April 1998 15:17 Subject: [OT] Isolation measurement >Hi there > >I need to measure the output from a circuit >that has a floating power supply. The circuit >that does the measurement has a 16C71 >and its supply is referenced to ground. > >The circuit with the floating power supply >produces a voltage in the range of 3V to 9V >and I need to isolate it from the PIC and >bring it down to within the limits of the PIC's >AD converter. > >Is there a simple way of using OP-Amps to >provide the isolation or another method that >does not cost much? > >Regards > >Gavin >-------------------------- >vulcan@ihug.co.nz >http://www.geocities.com/TheTropics/Cabana/2625 >-------------------------- >