On Tue, 13 Jul 1999 01:13:23 +1200 Russell McMahon writes: >I have used both a standard microprocessor input pin as the sense >element (PIC) and an internal comparator (Z8) and an external op-amp >(LM324) as comparator. I am aware of the poor performance of the >LM324 as a comparator The 324's comparator brother the 339 (also offered in a dual unit, the 393) should be about the same cost. But then you need two chips unless you can make the 339 work well as an amplifier. There was a chip with 324 type amplifiers and 339 comparators on one chip. It's likely been discontinued. Probably the major problem with the 324 is its low bandwidth. If you slow the whole process down it may work better. Amplifying the signal before appling it to a MCU pin ought to improve that method. Metal-gate (4000 series) CMOS gates biased into linear operation make decent rock-cheap amplifiers. The 4069UB is the best choice, but other gates will work if you happen to also need a logic gate in the circuit. Also, amplifiers made from 2-input gates can be placed in low-power shutdown easily by a logic signal applied to the other input. These amplifiers are maybe not so good for DC precision but work well with small high-impedance AC signals. ___________________________________________________________________ Get the Internet just the way you want it. Free software, free e-mail, and free Internet access for a month! Try Juno Web: http://dl.www.juno.com/dynoget/tagj.