Accurate Keg Monitoring System

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How Did I Do It?

I decided that an external scale was the only way to do this. I still don't like the flow type systems. I personally close my tank valve until I need it and then just open it for a short time and shut it off. This obviously would affect flow. So, I figured I would weigh the empty cup or mug and store that value, then weigh the full cup or mug and subtract the first value from the second, giving me weight of beer! Here is the scale I bought from Amazon for $6.99 SHIPPED!

I took this baby apart, removed the existing electronics to expose only the load cell, and started testing with my Arduino. Here is an image of the completed scale circuit.

You will notice two chips. the one on the left is an AD620 Instrumentation Amplifier. It takes minute changes in voltage and allows them to be amplified up to 10,000 times! The chip to the right of it is an ICL7660 Voltage Converter. It takes V(in) and makes it = -V(out). This is important because the AD620 requires both +5VDC and -5VDC. I know there are other In-Amps out there that are single supply, including the INA125, which I tried! The results between the two were not even close. Buy the AD620 and spend the $2 for the ICL7660. Your results will be much better and the ICL7660 is just cool! The only other thing you'll need is an Arduino board. Any one will work. I use the Uno and an XBee to wirelessly transmit the data to my PC. Check out the image below.