how to connect 4 wire load cell to load cell combinator

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junke715
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how to connect 4 wire load cell to load cell combinator

Post by junke715 » Tue Nov 28, 2017 9:06 am

i purchased 4-wires load cell, as well as the load cell combinator. but the combinator is for 3-wires load cell, i wonder if there is any way that i can connect them and get correct readings?
help is needed!!
thanks in advance

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DanV
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Re: how to connect 4 wire load cell to load cell combinator

Post by DanV » Tue Nov 28, 2017 1:48 pm

The combinatory is clearly for connecting 4 load cells (or half load cells) together and then to an amplifier.
What you appear to need to connect your 4-wire load cell is just an amplifier HX711:
https://learn.sparkfun.com/tutorials/lo ... okup-guide

junke715
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Re: how to connect 4 wire load cell to load cell combinator

Post by junke715 » Wed Nov 29, 2017 5:17 pm

but i have four load cells, so i dont need combinator?

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DanV
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Re: how to connect 4 wire load cell to load cell combinator

Post by DanV » Thu Nov 30, 2017 8:13 am

Well, that's not exactly what you said:
i purchased 4-wires load cell
which sounds to me like a single 4-wire load cell.

The combinator takes four 3-wire load sensors and connects them as a wheatstone bridge, then the combinator connects to the amplifier.

The load cell (4-wire device) is already a wheatstone bridge designed to be connected to an amplifier.

Unfortunately, I can find no information on connecting a 4-wire load cell as a 3-wire load sensor.
I suppose you could use a multimeter to find the variable leg of the load cell and its neighbor resistor and use it like a 3-wire but I can't confirm this.

deenlee
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Re: how to connect 4 wire load cell to load cell combinator

Post by deenlee » Wed Apr 04, 2018 11:19 pm

Very real for me now, came with the same issue here. I found different advices in the web, including different schemes and infographics, but only this thread is really helpful. At the moment planning to order more load cells from Tacunasystems.

jfkreuter
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Re: how to connect 4 wire load cell to load cell combinator

Post by jfkreuter » Sun Aug 19, 2018 11:32 pm

Hey, I also have exactly the same problem! I find it strange that Sparkfun sells 4-wire load cells, amplifiers and a "load cell combinator" and there`s absolutely no documentation about connecting all of this. For the 3-wire load cells from bathroom scales, yes, but not the 4-wire cells which are actually sold by sparkfun.

Has anybody here found a solution to this yet? I would greatly appreciate a tip in the right direction because this is what's blocking progress on my project at the moment.

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DanV
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Re: how to connect 4 wire load cell to load cell combinator

Post by DanV » Mon Aug 20, 2018 8:40 am

Not sure what your situation is - multiple 4-wire load cells and a combinator?

The Hookup guide for the HX711 Amplifier:
https://learn.sparkfun.com/tutorials/lo ... okup-guide
and Getting Started with Load Cells:
https://learn.sparkfun.com/tutorials/ge ... load-cells
both provide a ton of info.

However, the distinction between a load cell (4-wire) and a load sensor (3-wire) is not made clearly enough!
HX711 + one 4-wire load cell = success.
Load Cell combinator + four 3-wire load sensors + HX711 = success.

I think the Load cell combinator should expressly say IT IS NOT SUITABLE FOR USE WITH 4-wire load cells!

jfkreuter
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Re: how to connect 4 wire load cell to load cell combinator

Post by jfkreuter » Wed Aug 22, 2018 2:18 am

Hey, thanks for your answer.
Yeah, that`s the situation.

I want to weigh spices and was planning a three-point system to hang up the "weighing funnel". So i have three 4-wire load cells and the combinator and an hx711 amplifier.
I read through the tutorials you posted thoroughly and I`m able to get correct and reproducible readings with one load cell + amplifier.

Do i read your post correct in the means of "the load cell combinator does not work at all with 4-wire load cells" ?

Then i agree with you, that should be included in the description of the combinator. I`m sure its not the first time somebody wanted to combine the load cells and the combinator in this way.

Do you know your way around load cells? Do you know if there`s a way to connect the 4-wire cells to give out a cumulative reading?

Edit: I want to weigh actual spices, not what a friend of the green stuff would name "spices" ;D

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DanV
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Re: how to connect 4 wire load cell to load cell combinator

Post by DanV » Wed Aug 22, 2018 2:08 pm

The issue:
A load cell is a Wheatstone bridge with one variable element. Connect it to n amplifier and away you go.
A load cell looks like a voltage divider with one variable element.

I suppose you could measure the wires on a load cell to determine where the 3 significant wires are that could make it look like a load sensor, but the element resistance values could be far from that of a load sensor - I just don't know.

I would get a beam style load cell (5Kg : https://www.sparkfun.com/products/14729) and hang your weighing pan from it then use the HX711 or the OpenScale https://www.sparkfun.com/products/13261.

But, that's just me.
You could possibly use three HX711's with your three loads cells as three inputs to your arduino and sum them up but that sounds iffy.

jfkreuter
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Re: how to connect 4 wire load cell to load cell combinator

Post by jfkreuter » Thu Aug 23, 2018 12:01 am

OK, so there`s no stupid simple way ;)

I`ll carry on building and use only one load cell for measuring and the other two as fix points. That`ll work with my geometry for now.
I`ll figure the other two sensors out on the way.

I can`t let the funnel hang form the top, because of geometrical fix points, and i like the small load cells because i hope they give me more accurate measurements. I have to weigh small amounts up to about 500 g/17 oz and down to about 20 g reliably.

I actually have three amplifiers and an arduino mega, but i might run out of pins with three load cell amplifiers. I have to control a bunch of motors too ;)

Thanks for the clarifications on the combinator and the load cell/load sensor story, I`ll post again if there`s something to show to the world.

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