Problem developing a weight scale ( Load Sensor Combinator + HX711)

Other Hardware Sensors
1

Hello, this is my first topic here in Arduino Forum, but i'm planning to be a active user, help and being helped :slight_smile:

But now i really need some help D:

I am using this combinator with 4 Tal220 Load Cell and a HX711 ADC Amp, but when i run the code with nothing on the scale, and the read value is constantly increasing ( starts 0.00 lb, up to 0.01, etc), but i'm really not understanding why this is happening.

All the load sensors have been testing alone and worked great. I also have already checked all the connections and is accordingly the Sparkfun tutorial that i followed. I will put above the links of sources that i used.

HX711 Arduino Library : GitHub - bogde/HX711: An Arduino library to interface the Avia Semiconductor HX711 24-Bit Analog-to-Digital Converter (ADC) for Weight Scales.

Load Cell: Load Cell - 10kg, Straight Bar (TAL220) - SEN-13329 - SparkFun Electronics

HX711 : SparkFun Load Cell Amplifier - HX711 - SEN-13879 - SparkFun Electronics

Load Sensor Combinator: SparkFun Load Sensor Combinator - BOB-13878 - SparkFun Electronics

Also, a parallel question : Which one of this configurations have better accuracy, or they have the same accuracy: 4 10 kg Load Cell or 1 40 kg Load Cell? Why?

thanks in advance ^^

2

Is this temperature drift perhaps? You have 4 sensors operating at different temperatures (after
you've been handling them), perhaps the configuration you are using is not temperature
compensated? Link to the tutorial you've used is missing BTW.

The higher the max load of a load cell the less sensitive it will be, since you are measuring
the ratio between a tiny signal against a large supply voltage. So the 10kgf one's are 4 times
better, everything else being equal. Also the geometry matters - with a single loadcell you
have the issue of correct alignment of the force, since torques and shears will confuse the reading.

3

Sorry for delay in responding, i was doing some test with the system. And thanks for your answer MarkT

Well, let me update the dev situation. I finally was able to get some constant readings with the sensor. The problem is that i'm not sure about the cause. First of all, some facts that i forget to say in the previous test is about where the load cells are being tested. I'm intend to use the load cells inside a supermarket car, in order to measure the weights of the products. The connection that i made is in the photo bellow

I put the 4 load cells in the middle of two mDF plywood plates with another mDF plate to make the struct parallel inside the car. The photo bellow shows better the structure

So, as i sad in the first post, i made test with the system already built into the car and, after some tests, i decided to test a single load cell without taking out the car and i realised that all the load cells have presenting the problem that i described in the first post. After that, i take out the structure and when i made tests outside the car the load cells started to get more reliables readings. So, when i put the structure inside the supermarket cart again, the system works!

I think that may be some part of the structure that wasn't put correctly, but i'm not sure. Someone know something that can help me to discover what happened? About the temperature, i believe that is not the problem, cause each load cell works outside the car, in the same temperature.

Besides that, i was wondering how can i make the system more reliable in weight readings. How can i compensate, for example, the temperature problem in the system? I don't know very much about Mechanics, but how can i improve my structure in order to mitigate the influence of vertical forces, and make sure that all the weight will be read by the load cell? I thought that some of these questions may be outside the scope of the forum , but if someone can point to me some link about these questions, will be very helpful :slight_smile:

Lastly, i'm not from a country with English as a native language, so i apologize in advance for any grammatical problem is this post ˆˆ

4

Sry the double post, but i need to say that the system still unstable. Today i put the system to run and back the same problem of values increasing unlimited that i have in the start. I rly don't know what to do D:

5

Do you have RF suppression capacitors in place - that's a lot of bare wires picking up signals there, I'd
suggest 10nF or more across the inputs to the amplifier to quell that possibility. RF direct into the input
of a sensitive opamp is bad news.