The digital weigh-scale(The Load Cell and HX711)

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Finally, the Wheatstone Bridge and some few more concepts we learned in school get applied in real life!! Isn't that exciting??

The load cell, as we said earlier , is used to measure electrical signal whose magnitude is directly proportional to the force being applied on it.

There are a variety of load cells among which I will be using a strain gauge.

Basically, the strain gauge measures the electrical resistance (which is proportional to the strain being applied) on the device.  Each strain gauge has a different sensitivity to strain. This is known as the Strain Factor or the Gauge factor(the ratio of the relative change in electrical resistance to the mechanical strain)  

So enough with the class stuff, lets get to the part we all like:

I had the worst time with this thing. Rule of thumb from me: Never trust everything as said by the manufacturer. They too make mistakes. Some of which may take you days to realize. Like me and the load cell & HX711.

So, the load cell may have four or five wires [RED, BLACK, WHITE, GREEN & YELLOW]. the yellow is optional, hence some strain gauges don't have it. Its used for grounding so as to lessen the EMI. In place of it, a black wire,foil or loose wires are used to shield the wires so as to lessen EMI.

The red, black, white and green come from the strain gauge on the load cell.

Every load cell has four wires that are hooked up in a Wheatstone bridge formation.

These wires are what connect the load cell to an Amplifier. This amplifier allows us to read the resistance changes in the form of units we understand. This is possible after some calibration has been done.

I will be using the HX711 Amplifier.



Excitation+ (E+) or vcc is RED
Excitation -  (E -) or ground is BLACK
Output+ (O+), signal+ (S+), Amplifier (A+) is WHITE
O-, S-, A- is green or blue

So, probably works for most of them, but I think mine had issues. After weeks of trial and error, self blame, and a lot of doubt on the machine, I learned that mine was just different;

BLACK   E -
WHITE   E+
RED       A+
GREEN  A -

Also a problem may come up in the readings, e.g. the values decrease as your weight increases. Then, you may have to interchange the O+/O-




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