I am looking for help with hacking a typical digital (body) weighing scale to use in a custom application. Is there some internal digital or analog output in body scales to directly get the measured values? How might I go about reading this output?
I thought about connecting the scale with an Arduino, Tinkerbot or Raspberry Pi for further processing, for instance to weigh other stuff and for home automation. I am not looking to build my own body scale from scratch, just adapt one to be able to extract the measured values. Body fat or similar nonsense (which cannot be measured reliably anyway) is not required.
Best Answer
Sounds not too difficult to do what you are proposing, most digital scales use 1, 2 or 4 strain gauges in a Wheatstone bridge configuration to form a load cell.
This load cell will output a small differential signal which is read by an Instrumentation Amplifier (InAmp) to amplify and output a single ended signal that can be easily read by an ADC.
So if you have a digital scale, it's just a question of hacking it and tapping this signal to be read by your PIC, Arduino, etc, to be used as you like (send to PC, display...)
As far as I'm aware the R-Pi doesn't have analog inputs available as "standard", and it sounds like complete overkill for this anyway (unless you are using the R-Pi in place of a PC or something)