Load Cell Experience

@fastrunner08 - I'm not a electronics hardware guy, so I can't answer your question, but do you have a link you can share for these units?  I might be able to help, if I looked that over.  I'm definitely interested in the load-cell unit itself.  I'm sure you've checked the ratings for taking the 9 tons... have you considered the transverse loads?  Do you plan on having panhard links to take the longitudinal and lateral loads?  9 tons of load wanting to shift driving over roads, pot-holes and emergency braking, sounds like a lot to take if you only plan on 4 (or even 8) of these to take all vertical and lateral loads.  Just a thought.  Got any pictures of the whole thing? 😀 Sounds like a cool, real-world project!

@fastrunner08 Hi, interesting project. Sorry, but Amazon links don't work here, use a shortener.

What is that device, what protocol will be used?

Oh yeah!  @fastrunner08 - I usually put the link in normal so we get the picture and also use it in quotes so we can dig it up also.  I think this looks to be the same one???

"https://www.amazon.com/Pressure-Force-S-type-Sensor-Cable/dp/B01F6IOWDG/"

@inq @fastrunner08 Now all we need is the data protocol.

@inq It is a walfront S-beam load cell.  Model # Walfront2oska6i7ev-04. 

The Spec sheet comes up if you throw that into google.  I didn't realize the amazon link didn't work. 

I don't have any photos yet of any of the set up because i'm just in the concept phase.  I can get some photos of the wagon, next time i have it unburied from the barn.  Lateral forces and loading was a concern of mine.  It would never be traveling faster than 15mph in on the road full, being pulled by the tractor.  My bigger fear is in the field where it will be the roughest, but travel speed at that point would be less than 4mph.  

I was also thinking of an air suspension system in combination where it holds the gravity bed on the running gears when to pressure, but then lowers completely, to put all the weight on the load cells for measuring when the wagon is stationary.  Of course that option, while much more durable would be $$$$$$. 

So i'm new to the term "data protocol" so correct me if i'm assuming the wrong thing. I'm using the Arduino HX711 library by Bodge.  I think it is just running an analog to digital converter protocol, which in this case uses 2 digital pins per HX711 chip connected to the UNO.  One pin for clock and one pin for data.  No Serial or I2C required.  I'm planning for the prototype to just use the serial monitor to output the measurements, but eventually output to an OLED screen, that will most likely be I2C.    

Posted by: @fastrunner08

I am planning to use the HX711 amplifier with them, but was wondering if anyone had advice on how i can wire them together to use fewer amplifiers than pairing one amplifier to each load cell. 

Again, I'm not a hardware guy... so this is just an idea I've picked up over the years.  There is a chip (< $1 or 2) called a Mux.  I have some (CD74HC4051E Mux) or maybe a Shift Register (74HC595N Shift Register).  I'm not sure the distinction and someone here can help you with an appropriate choice.

That I think might do what you need.  Basically it's a switching thing.  You tell it with several pins from your Arduino and it can re-route say... the four leads from one of your transducers to the amplifier, and take a reading.  Set the Mux to other values will send the data from the a second transducer.  On the Arduino, you just cycle through all the transducers one at a time.  I imaging it might only be several milli-seconds do do all of them... sum them up and you get the whole load.

@inq I assumed they were stationary under ground level pads he would drive onto to weigh the load. If not, maybe the lateral forces will be an issue.

@fastrunner08

Posted by: @fastrunner08

Hello Everyone,

I'm working on a project to apply these load cells to a gravity wagon on the farm to determine weight of crop placed in it. https://www.amazon.com/dp/B077YHFCX4?psc=1&ref=ppx_yo2ov_dt_b_product_details

To handle the load, i'm going to need to use at least four of these load cells, one on each corner that will be mounted between the gravity wagon hopper frame and the running gears (This is the section of the wagon that has the 4 tires frame, and two long wooden or in my case steel parrellel bars that the hopper mounts to).  I possibly will need to use 8 or two in each corner to give more support and balance the load.  Wagon total weight with wet corn it should not exceed 18000lbs.

I have seen some videos that link 3 wire load cells together, but not much on these ones. 

I am planning to use the HX711 amplifier with them, but was wondering if anyone had advice on how i can wire them together to use fewer amplifiers than pairing one amplifier to each load cell. 

I'm looking for any advice or links to ideas of how to wire the load cells together before running to the amplifier or if it isn't possible, and i just need to bite the bullet and get enough HX711's.  I am buying the sparkfun ones at about $10USD a pop. 

What a coincidence... this sounds like a great project!

I was actually looking into one of these S-type load cells (aside from many other types) recently, with the view to building an engine dyno (obviously using a larger cell, but the same type).

Look forward to your progress!

Cheers

@zander

Posted by: @zander

@inq I assumed they were stationary under ground level pads he would drive onto to weigh the load. If not, maybe the lateral forces will be an issue.

These S-type load cells can accept both tensile and compressive loads, thus if you design in such a way that via using tie rod end's, the load will always be correctly aligned to the load cell.

Cheers

Posted by: @zander

@inq I assumed they were stationary under ground level pads he would drive onto to weigh the load. If not, maybe the lateral forces will be an issue.

I might have miss-read the O.P., but I thought he wanted to integrate it into the trailer itself.  Basically, I was imagining he wanted 4 (maybe 8) to be the total load path from the bed holding the stuff and the frame.  I was just suggesting using several Panhard Rods to take ALL lateral, longitudinal loads.  18000lbs * multiple G's in a collision would certainly break those little things and have that load come crashing down on you in the truck cab.  

@inq I admit I did assume they were like a scale. I had a guy weigh my rig wheel by wheel and I assumed it was similar. If it's an agricultural application then it makes more sense to weigh as he goes to know when to leave the field and dump that load. Maybe the OP will clarify.

The mechanics of the situation I have pretty much worked out, the real question I had was around the wiring of them.  Does anyone know if it is possible to wire all these in series to one Hx711 or do i need 1 amplifier per load cell.  

Hi @fastrunner08,

   Sorry, I have only had a quick glance at the datasheets etc. listed below, so I could be missing the obvious.

Based on two example refs:

• https://circuitjournal.com/50kg-load-cells-with-HX711
• https://circuitjournal.com/four-wire-load-cell-with-HX711

+ datasheet & description

• https://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/hx711_english.pdf
• www.amazon.com/Pressure-Force-S-type-Sensor-Cable/dp/B01F6IOWDG/

It looks like the 3 wire load cells .. which have two resistive elements per cell, can be used in 1, 2 or 4 cells per HX711 configuration

However, the 4 wire load cell, is a complete Wheatstone bridge in each cell ... and it isn't obvious to me how three bridges can be connected together.

So far as I could see on the Amazon page, it lists 4 wires ... +E -E +S & -S

Implying a 4 wire load cell.

So my impression is you will need 1 amplifier per load cell, and hence need to measure 4 voltages, and sum the result in software.

I suggest you prototype the system before committing to the 'heavy duty' enginnering needed to implement the final project, if only on a limited basis at the 'lower' end of the scale of weights you intend to to measure. In particular, check for accuracy and drift, making sure they are within your requirements.

Best wishes and good luck, Dave

Posted by: @fastrunner08

The mechanics of the situation I have pretty much worked out, the real question I had was around the wiring of them.  Does anyone know if it is possible to wire all these in series to one Hx711 or do i need 1 amplifier per load cell.  

Already gave you a suggestion.  You must have missed it.  Look this over:

http://www.gammon.com.au/forum/?id=11976

You get four of these chips... Each chip would handle one wire coming from each of your 8 load cells.  It would require 3 digital pins from the Arduino to change which sensor ALL 4 chips are looking at, at any one time.  The output (1 wire from each of the 4 chip) would go to the Hx711.

Procedure:  Set the 3 data pins to select a sensor, take reading, select the next sensor, take a reading.  Daisy chain.  Depending on the update rate of the Hx711 would determine how long it would take to read all 8 sensors... probably well under a second.

@davee - Would you mind sanity checking my suggestion?