Portable, multi-channeled voltage sensor

microchip has several PIC's that come with Analog inputs i even think from Maxx you can get an io expander that would allow you to multiplex lines.

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Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

The problem here is the 'millivolt' part of the requirement. The ADC on the normal PICs is 10bit, and loses linearity below a Vref of about 2V. So the smallest 'step' resolution, is around 2mV. I cannot think of any micro, that has an ADC able to give good resolution to this sort of level, but the obvious answer is an analog multiplexer, followed by a gain stage. There are a few PICs offering higher accuracy ADC's (the 16C77x, with

12bit, and the old 14000), but even with these amplification will be needed for any reasonably resolution, and (assuming the source has a relatively high impedance), to meet the drive requirements of the ADC itself.... The sample rate is not a problem. Even the standard PIC ADC, can sample in the order of 30000S/sec, but if using a multiplexer (either external, or the one inside the chip), the time needed to select the new channel, acquire this, and then read this, needs to be included. The simplest solution, would probably be to use a buffer amplifier on each input, bringing the signal range up to about 2.5v peak. Then a 2.5v bandgap reference, and a chip like the PIC18F4515 (which already has a 13way ADC multiplexer), and about 3K of RAM, to hold readings. If more storage than this is needed, add an FRAM.

Best Wishes

The buzzword is Datalogger (or variations on that theme). A battery powered microcomputer with input circuitry for measurements and enough memory to save the information until offloaded. One name that comes to mind, for miniatures, was Onset(?). For regular sized equipment, Fluke.

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

Such a device is called data logger. All sizes and prices are available.

will list more than you care for :-).

Markus