What ADC does this wattmeter use?

[simingx]

This one... http://www.rc-cars-planes.com/rc-watt-meter_n.html?wurd5
To get 0.01A resolution out of 100 amps, you'd need at least 14 bits of resolution (0.006A/LSB)... does it really have one?

[AndyOne]

My guess is that it's autoranging as it only reads out to 4 digits.

Andy

[tclark]

I don't know what they use in that wattmeter, but the one I built uses the internal A/D (10-bit per conversion) in an Atmel processor. By having a dither on the incoming data, and averaging many conversions (it's been a while since I designed it, I think 2048) per sample, I get better than 15 bits of resolution.

-Tracy

[Mr.RC-CAM]

You can create N effective bits for every 4N (four raised to a power of N). That is, in a perfect world, 1024 properly acquired samples would extend a 10-bit A/D to ~15-bits. This only works if the lower order bits are "noisy" and the noise is Gaussian. YMMV.