[DegrawSt] uses four 50 kg load cells to create a bathroom scale using an Arduino. Load cells typically contain strain gauges that change resistance when deformed.

In this quick Arduino tutorial I will explain how you can control a relay using the Arduino Board, one 1K and one 10K resistors, 1 BC547 transistor, one 6V or 12V relay, one 1N4007 diode and a 12V fan ...

Looks like low-end load cells might not be up to measuring the output on your high-power pneumatic tools, at least not repeatedly, but they ought to hold up to most electric drivers just fine. And ...