How to measure Current with a Pic

[circuitpro]

I am working on a project in which we are using a LMP8601. This part converts the current through a shunt resistor to a voltage that can then be measured by your PIC's A/D converter, or in our case, we are feeding the output to a window comparator for a "go-no go" digital output that goes directly to a PIC i/o pin. This part is available from both Mouser and Digikey I believe. The theory is explained pretty well in the datasheet.

[languer]

The key to your request is the following (imho):

The load can be between 0 and 20 amps. I would like to be able to monitor the current in to the PIC.

If you want to monitor current from 0 to 20A (both ends inclusive), then the Allegro parts are probably best.

However, if all you need is to set a reasonable trip point (e.g.) 10A at which an overcurrent signal trips; then a sense resistor followed by some form of a comparator is probably easiest and less expensive. We have normally used something like the LT1787 with multiple parallel power-rated 0.1ohms or less sense resistors. The power rating will depend on how many sense resistors are in parallel, how much margin you deem necessary above your maximum current.

[Charles Linquis]

I'm a fan of the Allegro devices. So much simpler than dealing with low-value shunt resistors. Isolated too. Unless you have a pretty good understanding of analog, just use an Allegro. Up to 30A in an SO-8 package. The offset from zero is about 10% of the supply and the output is linear - 133mV/Amp.