Hi MarkT, I ordered a couple of these chips and they arrived today. Man those things are TINY!! They are so small I lost one when I opened the package. Several times I thought I'd found it but it turned out to be a bread crumb!! I should hopefully be able to solder it still :-)

With regards averaging using the arduino wouldn't this be a problem if it gets busy doing something for a short period of time? You would end up affecting the readings. On the other hand wouldn't a cap be a lot simpler?

I am curious about using a hall sensor but am wondering how they manage to only pickup current from wire in question. Wouldn't they be susceptible to other electrical interference?

Hi Mark, thanks for the reply. That chip looks like it's exactly what I need. I like integrated packages like this :-) From what I understand I can just hook up 12V to power the chip, either side of the shunt to V+ and V-, a resistor to the output and it's done. I would then just need a resistor and cap to smooth out the voltage. I believe it is average amps I am after, whatever you get if you used a voltmeter. Basically I should be able to multiply amps x volts x time to get the amount of capacity taken out of the battery. Is there anything else I would need to add to the circuit, say for protection due to spikes etc?

Cheers,
Michael

I wish to measure current up to 150A in an car using a shunt. I have three different problems with this. The first is that I cannot place the shunt on the negative wire because I will need to isolate parts like the alternator from ground. This causes the problem that each side of the shunt is 12+ volts and the arduino measures only up to 5. The second is that I need to amplify this signal up to improve its accuracy as I only have 1mv per amp. The third is that one of my loads is an inverter. Being that an inverter outputs AC I have found that the current running into it goes near zero 100 times per second. Because the arduino takes reading very quickly it is sometimes showing a high reading and sometimes showing near zero, pretty much at random.

So what I need is something that will isolate my 12V signal, amplify the voltage drop across the shunt and then smooth it out. I kind of know what I need, an op amp and an RC circuit to smooth it out but not sure of the specifics.

Thanks in advance.
Michael

See this post. Different pins are used on the mega
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1282386473