I am trying to make a scale and I want to connect 2 5kg load cells together to one HX711 amplifier, which connects to an Arduino Uno REV3. How would I be able to go about this?
For more information about the electronics, they are linked below.
5 Kg Micro Load Cell - RobotShop
HX711 Load Cell Amplifier - RobotShop
The 5 kg load cell you linked appears to be a complete Wheatstone bridge sensor, and only one of those should be connected to the HX711.
Why not use two HX711 boards.
There is a HX711-multi library that lets you connect one or more HX711 boards to your Uno.
Clock can be shared, so you use only three pins for two boards.
Leo..
Okay, I assume it'll be the same as if you were to connect two load cells together and the Uno would read the overall value but, how would I connect the HX711 boards to my Uno? Could you explain further?
How do I share the clock line and such? And what pins would be used on the Uno board by the HX711 boards?
EDIT: I have thought about it further and am not entirely sure but do I solder the CLK pins of both the HX711s with wires and then connect to the Uno, and then their DAT pins separately to their respective pins on the Uno. What about the VCC/VDD pin? I was thinking of shorting them together and connecting them to a voltage pin(eg 3.3), so I can use the other voltage pin for another component(say a potentiometer or LCD, something else et.). So I am unsure about that as well.
No, not at all.
Spend a couple of moments with your favorite search engine to look up things like "multiple hx711 arduino library" and discover web sites like this one:
With wires.
The clock wires of the two HX711 board can be connected to one Arduino pin,
but they don't have to. Up to you. The data lines need their own Arduino pin.
Each board needs of course 5volt power and ground.
Most HX711 board are 5volt-only, so I don't know why you mention 3.3volt.
And you said you had a 5volt Uno R3.
Breadboards are commonly used for that. At least in the testing stage.
Leo..
So to sum up, I just connect only one HX711 amp CLK pin to an Arduino pin, and connect the HX711 amp power pin to the 5V in parallel on the breadboard. Just to confirm?
If the load cells were half Wheatstone bridge, would I have been able to connect two to one Arduino?
And the reason I had decided to use two 5k load cells instead of one 10kg is because I thought it would perform better. Would I be better off using just one 10kg load cell?
Thank you, I have taken a look. I have come across the fact that using two HX711 amplifiers would make it asynchronous. Would this mean that the values read from the load cells would come up one after the other, instead of together and combined? Bit confused with the asynchronous situation.
Are you trying to measure a max load of 10kg or 5kg?
Two 5kg doesn't equal one 10kg
Max load of 10kg. I didn't know that 2 5k equalling one 10kg isn't the case. I figured it would give a more accurate reading, but I am guessing now it is just better/right to use a single 10kg load cell?
If so, would you be able to explain further please?
Yes, of course. Do with the two values whatever makes sense for your overall project, whatever that is.
because I thought it would perform better.
For what purpose, and "better" than what?
I would want the two load cells to act as one(by connecting to the hx711 amp) to measure the weight of an object I put on the scale. The reason I wanted to use two load cells is that the scale design I am interested in is rectangular, and the object placed in the middle. I feel there would be better support and more accurate readings with two load cells placed on either end, as opposed to just one load cell in the middle, which I feel would also need extra support to hold the load up(would that not affect the reading that comes out?)
If I use 2 5kg load cells, and the object that I place on the scale is 7kg, what would the HX711s read? I would have wanted just one reading returning 7kg, but I feel that wouldn't happen, as from what I can understand from this thread, they'd only be able to read up to 5kg and return them separately up to 5kg. I don't think one load cell would read 5kg, and the other 2kg. I don't think it will work like that.
Essentially, I would want a scale that works like this:
50kg Load Cells with HX711 and Arduino. 4x, 2x, 1x Diagrams. - Circuit Journal
the x2 version, but unsure as to how to do that with these load cells. The max load doesn't have to be 10kg, so I am okay with just following this example if I am unable to do it with the micro 5kg load cells. I take it that because of their Wheatsone bridge configuration, I can't combine them together like the ones in the example?
A scale, and better results in term of accuracy.
You can use either one 10kg load cell or two, three, four, etc. but they must all be 10kg
If you have a big platform then use three or four.
If you use four, one in each corner, then you just simply add all the weights from the four load cells to get the actual final weight.
You will need four HX711s.
Accuracy depends entirely on how well you calibrate the scale. You will need accurate test weights to do that.
Your approach will work fine, just add the two individual measurements to get the total weight (after taring and calibrating each sensor).
Each individual sensor introduces its own errors to the measurement and they are independent, so the total error can only increase, as you add more sensors.
For two sensors, the estimated total error is sqrt( sensor1_error^2 + sensor2_error^2).
You can only do that with 1/2 bridge load cells, so you would need to find 4 10kg 1/2 bridge load cells, but probably won't
Okay, I've searched around and can only ever see 50kg load cells that are half bridges. So to clarify, if I were to use 4 of them connected to one combiner board and then hx711 on a rectangular-shaped scale(the cells placed on each end), would the total weight then be 200kg? And if something less than 50kg were to be put on the scale, eg 34kg, would it return just that value(after tare and calibration of course)
I would have figured the two load cells would read and return the same value of the total weight, so if I were to add, wouldn't the value just double? For example, if I were to put a 2kg weight, and add the two returned values of the load cell, I would get 4kg instead of 2. I think I am misunderstanding something here
With two cells, on each end of a platform, the added weight will be unevenly distributed on the cells, unless is it exactly centered. If it is perfectly centered, each cell supports half the weight.
These are things you can test for yourself.
Say you had a steel plate 1 meter long and 15cm wide and you place one 5kg load cell at each end.
Now you place a 10kg weight 1/4 meter away from the center towards one end.
What do you think each load cell will measure?
5kg each?
No, one will measure 7.5kg and the other 2.5kg.
So can you measure 10kg with two 5kg?
The answer is NO.
It doesn't matter if they are 1/2 bridge or full bridge, unless the weight is evenly distributed or centered between the load cells you may exceed the range of an individual load cell.