Reading a cycling voltage, capturing the peak value?

Turnbull2112

I have a voltage I'm reading from a process that cycles from let's say 2 to 4.5 volts every 40 seconds or so. How can I take a "snapshot" of the maximum voltage from the peak of each cycle and average the peaks? Is there any way to take the duration of the peak into account as well? I'm not sure what commands to use here. The voltage I'm reading is going to be scaled into 0-100%. Thanks

erco

You're using an ADC or RCtime to measure the voltage using a Stamp?

Make a loop that constantly measures the voltage as quickly as possible, updates the stored max value only if the current value higher than the previous stored max value. After the value decreases beyond a reasonable amount, call that a peak value, store in a word-sized accumulator, and update a sample counter. Average value is accumulator/samples.

Martin Hebel

There's also a peak-hold circuit using an op-amp that may be of use. It entails an op-amp (LM-358), diode, and cap on the non-inverting input. The capacitor will charge to the maximum value, and the diode will prevent it from discharging. This will lock in the peak for a little while. Without drawing it out, the op-amp is in the voltage follower configuration, with a cap to ground from the non-inverting input, and a diode in series with signal. A better means is to use another op-amp instead of the diode (to prevent the 0.7V drop). This web page has a java applet showing one in action.
http://www.falstad.com/circuit/e-peak-detect.html

Note, once charged, the cap must be discharged (reset). A transistor controlled by the controller could be used to "dump" the charge.

-Martin