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Topic: Measure 4 load cells with 1 HX711, shift registers and Arduino Uno (Read 1 time) previous topic - next topic

witzlprmft

Hello to all of you,

I have a question about measuring multiple weights (outputs of load cells) with one HX711 and one arduino uno. Because the HX711 is build for measureing only one weight I want to use a shift register to "loop" through 8 load cells (4 full bridges). Is this possible? Is this how I can use a shift register (74HC595)?

This is how I think it could work:

The HX711 is connected to the arduino (as usual).
All 4 bridges (load cells) are connected to the HX711, without connecting the VCC (5V) from the HX711 to the bridges.

The shift register controls that only one bridge at a time gets the VCC (5V). My hope is now that all the other bridges which get no VCC give a signal of 0, so only the bridge supplied with VCC from the registers gives a signal to the XH711 which can be read by the arduino?

Do you think this is possible?

Thanks for any help or suggestions, I don't want to buy 3 more HX711 or 3 more arduinos =)

Greetings,
Mo

Grumpy_Mike

Quote
Do you think this is possible?
No, this idea will not work.
A load cell that has no power supplied to it nevertheless has an impedance and this will distort the signal of the one with power attached to it.

The load cell is simply a Wheatstone bridge click the link and you will see it just contains four resistors.

witzlprmft

Thx for your fast answer.

You are right, the measurement on a bridge without VCC still gives a reading (of course...).

So just in case if some other stumble across his problem:

You can measure 4 different weights with load cells like this:

- 4 load cell full-bridges
- 4 HX711 - You can buy HX711 quite cheap (4 pieces - 4€)
- 1 Arduino

-> You can connect all 4 HX711 to the same clock pin, the same GND and the same VCC on the arduino.
-> So you need just 4 digital input pins on the arduino to connect the signal of each HX711 to the arduino.
-> To use 4 HX711 at the same time you need to use this library for the HX711:
https://github.com/compugician/HX711-multi#hx711-multi

Good Luck with your projects.

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