There are many peak-hold circuits in application notes. I haven't got anything on PC but look at Linear Technology's site - they are SURE to have something suitable. Many others will have as well. Basically, for a positive peak detector, you use an op-amp with signal applied to the non-inverting input to drive a capacitor on the non inverting input high via a series diode and resistor from the output to the inverting input (diode anode to IC output). For a negative peak detector swap the op amp inputs and reverse the diode. A high value bleed resistor from the capacitor to negative rail for the positive detector and to V+ rail for the . negative detector slowly "resets" the capacitor after a period of no signal. Without this bleed effect the highest peak will be held for a long time if the input signal decreases. The above is just a skeleton but should be a good start. Very good compliance to true min/max can be expected. Russell McMahon _____________________________ - www.easttimor.com Updated regularly: 100,000 refugees STILL in West Timor face starvation! - www.sudan.com And you think Kosovo and Chechnya are bad! What can one man* do? Help the hungry at no cost to yourself! at http://www.thehungersite.com/ (* - or woman, child or internet enabled intelligent entity :-)) -----Original Message----- From: Grant Forest To: PICLIST@MITVMA.MIT.EDU Date: Thursday, 30 March 2000 23:14 Subject: [OT] Measuring Peak to Peak >Goodday, >Have a problem where a 500mV P/P sin wave varies. >Not sure if its the $3000 Cro I'm using or the wave it self. >Has anyone got a circuit or known's of an IC that will give the Max +ve >peak >and the Max -ve peak as two DC values that I can then measure with a 4 1/2 >DVM. >I'm looking for changes in the order of 0.1mV. >Tks >Grant Forest >