Does anyone know how I can connect an Arduino Uno to the LCD display of a bathroom scale? Context -- this project is a hack, its essentially a joke where no matter what you put on the scale it'll show the same weight. So I'm thinking all I really need is a touch sensor, my Arduino, and an LCD display.
But I'm interested in seeing if I can re-use the scale's existing display since it has a very nice blue lighting to it. There are only two wires going into it - black and red.
In general if I did want to intercept/read that data coming from the scale's load sensors could I hook up to the existing board or would I need to use something like the HX711 that I see ppl recommending for a DIY scale?
That would be an extremely bad transgression of forum protocol!
OK, I hope that you can successfully reassemble it.
If you want it to read exactly the same whatever is placed on it, that part is fairly easy. You need four resistors and a potentiometer.
Disconnect all four load cells, and measure between black and white wires. This should be twice the measurement as between white or black, and red. Choose four resistors of vaguely similar common value as half the black-white value. Connect a pair in series between "E+" and "E-" with the centre tap to "S-". A second pair in series with a potentiometer in between, the potentiometer value being (approximately) one tenth of the resistor value. The ends again connect to "E+" and "E-" with the potentiometer wiper to "S+".
Now you have the ability to set the indicated value to whatever you want, however the behaviour of the scale logic is that it only switches on when you change the setting.
I will move on at this point to see how you follow this.
You forgot to count the 16 contacts on the edge of the circuit board. Those are pressed against the "zebra connector" on the edge of the LCD. The zebra connector is a strip of rubber with alternating conductive and non-conductive layers. When the two sets of contacts are lined up and pressed to either side of the zebra strip, one or more conducting layers connect the corresponding contacts while the insulating layers keep them from shorting to adjacent contacts.
You should be able to drive the LCD with an Ardiuno. Use this little sketch to alternate A0 and A1 on an UNO:
Yes, especially for a beginner. The LCD will be destroyed if segments are subjected to a constant DC voltage for a significant length of time, for example if one or more segment driver pins are stuck high, as a result of a programming error.
, and I tried both with the two and four but am getting nans. The calculated calibration offset value says 0.0.
I know the load cells work Bc the scale was working before…
Any ideas on how to debug the HX711?
Arduino is brand new, I'm using the default pins 4 and 5.