Measuring weight

Hi,

I've recently bought some load cells from "dollatek" on Amazon. It didn't come with a datasheet or anything and now I'm not sure how to use it (I'm a bit new when it comes to arduino).

After some intense googling, I came across this pdf which looks a lot like the load cell that I've purchased (the difference is that I've got a white wire instead of a blue one). This document didn't help me a lot either since there is some inconsistency in it.

I've also come across posts like this and after following the instructions of that post, I didn't get any results.

Can someone help me with this issue? Many thanks in advance!

As you have discovered, it really makes no sense to buy parts with no documentation.

Get some new load cells, after deciding what characteristics are best suited to your purpose, and follow a decent tutorial.

Avoid Instructables as most of them are crap, written by people who have no idea what they are doing.

@jremington I wasn't aware that there was no documentation. Instead of throwing these load cells away and buying new ones, I'd like to at least try to get some results.

A link to the original listing might help us understand what you have.

Do you own a multimeter?

@JohnRob thank you for your quick answer.

I've got it from here (it's in german).

I do not have a multimeter. Like mentioned in my post, I do not have a lot of experience regarding physical computing.

OK, I'll give you a lesson on how to approach such a problem:

  1. I looked a the photo on your link. Then searched google for something that looked similar:

Google Similar load cell

The from the title I googled "50KG Body Load Cell" and found this Sparkfun and this Instructables

Sparkfun is a solid source of information. Indestructible is kind of iffy as the authors range from pretty smart to inept.

Good luck

John

@JohnRob thanks for the links. The link from Instructables is one that is based on 4 load cells for weighing items whereas I am using a single one (I believe it's called quarter-bridged?). I'm using it to calculate impact of certain items when thrown or swung at the sensor. I have HX711 modules to read the weight that is applied on the load cell but I do not know how to wire it correctly.

I appreciate your help to show me the right direction in problem solving. I am pretty good at finding the right pages in order to hack my stuff together but this is one of the few times where I'm completely stuck. The links you've shared contain some additional information yet none of them show me how to wire the load cell with the load cell amp (the HX711 module).

The .pdf you linked to in your first post explains it all.

If you only have one load cell (half bridge) then you must make a second 'dummy' load cell with two 1k resistors. Then use the load cell and the dummy cell to make a full bridge for the HX711.
Leo..

As Leo said you need another set of resistors to created a full bridge. See the sketch attached. The Rpot should be about 10 ohms but sometime that will be hard to get. I would try for 50 ohms if you can find one. This pot will be your "zero" adjust.

John

Bridge.png.jpg

Note: If you can mechanically accomplish it, you could use two loadcells in mechanical series. In this case the Red wires would go to the amplifier and the other will be wired with one set of colors swapped.

Bridge.png.jpg

You need 1% or better resistors to make a decent reference half-bridge. Metal film, not carbon, preferably.

@Leo thanks for your reply. I have 1k resistors. Although, I do not think they are good enough, considering @MarkT 's comment.

In this topic, you mention that I should wire the wires, based on what values the multimeter gives me. Can you elaborate or give me a link where this is explained?

@MarkT would this suffice?

@JohnRob I'll dig a bit deeper in your sketch, thank you very much for your help so far!

If you have a multimeter I would measure the wires on your sensor(s) to see if they matchs the ones in Step 2. If the measurements match you know what your have.

instructables 3 wire

@JohnRob thank you for the quick reply. I have measured and the wires match as in step 2. Where my confusion starts (and maybe someone pointed this out before but, like I mentioned, I'm quite new to this stuff), is where to put those resistors (the 1k resistors) and to which parts of the HX711 I connect those wires.

edit
Setup that I've tried so far:
white -> E-
black -> E+
red -> A-

Unfortunately, the readings of the "calibration program" remains 0.0 :frowning:

The metalfilm resistors you linked to are fine.
If you have a DMM, then measure/select an identical pair.
Doesn't matter what value they are, as long as they are the same, or as close as possible.

Show us a picture of your setup if you're having problems.
Leo..

@Leo This is how I wired it.

I will buy those resistors, just to be sure.

edit
Eventually I want to connect 6 Pieces of them, each individually being able to measure applied force.

Wiring is not correct.
The load cell output goes to one A input.
The voltage divider output goes to the other A input.
Leo..

The load cell output is the red wire in this case yes?
What would the voltage divider be in this case?

albertdavid:
What would the voltage divider be in this case?

The two 1k resistors.
They divide the voltage from E+ in half, and connect it to A- (not A+ as you did).
Those resistors mimic a second load cell for the second input of the HX711.
You didn't buy a second load cell for a "full bridge", so you need to replace that with fixed resistors.

The red wire is the load cell output, and connects to A+.

You did connect the resistors to the red wire, which is wrong.

One resistor goes from E+ to A- and the other resistor goes from A- to E-
Leo..

Wawa:
The metalfilm resistors you linked to are fine.
If you have a DMM, then measure/select an identical pair.
Doesn't matter what value they are, as long as they are the same, or as close as possible.

Show us a picture of your setup if you're having problems.
Leo..

Why you need 1% resistors is not necessarily the precision itself, its the well behaved temperature coefficient.

@Leo I've got it wired as following:

Red (from the load cell) with A+
E+ with A- (with a 1k resistor)
E- with A- (with a 1k resistor)

[edit]
My load cell is not giving me anything. Are you sure that I only need to connect the red wire of the load cell?