Single half weathstone bridge load cell with Hx711 problem

Other Hardware Sensors
1

Hello,
Today I attempted to make a serial scale with a single 3 wire half Wheatstone bridge 75K load cell (YZC-161D) and an hx711 amplifier

I've seen a circuit on google that show's how you can connect the single load cell to the hx711 by replacing the other load cell with 2 resistors with the same value as shown
here:

http://postimg.org/image/5f5lwz751

and connected it to my hx711 as shown here:

http://postimg.org/image/axoz34hnh

I measured the resistance between the legs and here are the results:

white - res = 1k
white -black = 1k
red - black = 2k

So after that I used the Hx711 library for arduino made by Weihong Guan

and ran that sketch

#include <Hx711.h>
Hx711 scale(A2, A3);

// Connected A2 to DT
// and A3 to Clk

void setup() {
Serial.begin(9600);
}

void loop() {
Serial.print(scale.getGram(), 1);
Serial.println(" g");
delay(200);
}

After opening the serial port to see the results no matter how hard I pressed on it or what load I put on it it always showed 0.0 g

Can anyone tell me make am I doing wrong , if there is a simpler way, other way or noway to do it?

Thanks for your time.

2

You mean the white by saying grey?

3

I have deleted that post, because the first image appeared to be consistent with other sensors.

Are you sure you have the largest resistance between black and red...
If so, black and red go to ground (-E) and supply (+E).
white/grey goes to a sensor input, e.g. A+.

Most sensors I see on the net have red as output (A+), black as ground (-E), and white as Vref (+E).

The two resistors in series go between +E and -E.
And the centerpoint of the resistors goes to the other input (A-).
So your diagram #two is wrong.

You can also use two of these single sensors.
One to input (A+), and the other one to input (A-)
Swap the supply wires of ONE sensor.
forum.arduino.cc/index.php?topic=343054
Leo..

1 Like
4

Wawa:
I have deleted that post, because the first image appeared to be consistent with other sensors.

Are you sure you have the largest resistance between black and red...
If so, black and red go to ground (-E) and supply (+E).
white/grey goes to a sensor input, e.g. A+.

Most sensors I see on the net have red as output (A+), black as ground (-E), and white as Vref (+E).

The two resistors in series go between +E and -E.
And the centerpoint of the resistors goes to the other input (A-).
So your diagram #two is wrong.

You can also use two of these single sensors.
One to input (A+), and the other one to input (A-)
Swap the supply wires of ONE sensor.
forum.arduino.cc/index.php?topic=343054
Leo..

Your last post actually helped me thanks.
It works now but I don't how precise it is because when I try to calibrate it in the sparckfun HX711 library and put a 50g weight on it and then calibrate the output of the serial port to that value and then put a weight of 20g it shows me a greater value or no change at all from 0.

and when I put alot of pressure on with with my thumb and leave it it completely off set its self.

5

Did you measure the midpoint voltage of the sensor and the midpoint voltage of the resistors.
If the resistors are not exactly the same, the IC might get out of range.
What is the voltage (millivolts) between A+ and A- without weight.
Leo..