knut_ny:
..read the value:
Instead of: Serial.println(avg);
do Serial.println((5219-avg)/114.4;

You should be able to find these parameters based on [u]your[/u] readings/numbers

Or, follow the "how to calibrate your scale" procedure in the bogde/HX711 library "README.md", except the initial calls (to establish the "tare") are with zero differential voltage, and the subsequent calls (to establish the "scale") are by applying a "known voltage" (not a "known weight").

Alternatively, you could ditch (not use) the bogde library and just use the code in the last post in this link. Then, to determine the equation you seek:
- First, apply, say, 0 mV and note the "count" (as unsigned long). Take multiple readings and average them if you want...
- Then apply, say, +15 mV and note the new count.
- Use those two pairs of values to determine the equation of the straight line between those points (google it if you don't know how), where "voltage" is the ordinate value (vertical or "y" axis) and "count" is the abscissa (horizontal axis or "x" axis). The equation will be of the form y = m*x + b, where y = voltage, x = count, and m and b are constants that you determine from the two pairs of values.
Then you can apply an arbitrary voltage, get the count, plug that count into the equation, and then you will know the voltage.

Or, you could keep the bogde library and just do the same process with the 0 mV and 15 mV values in your first post (assuming those are reliable counts...and they probably aren't, since you seem to have violated the common mode voltage limit of the hx711).

The above must be done keeping mind Wawa's warning about *not* sharing grounds.

And, as Wawa said, keep the differential input voltage less than 16.8mV if you are using the default gain of 128 (judging from your last post, you don't seem to be "listening" to him). The code in the above link is based on the 128 gain.

PS: For calibration, you could use more than two points and "fit" a line through the points, but judging from your questions thus far, it's probably best to keep it simple at first and use just two points... :)

PPS: When you get data you don't understand, it is often helpful to graph it. A good homework exercise would be to graph the data in your first post (except not the two huge values at +5v and -5v).