Load Cell Setup and Components

@Leo
Why would the ADS1115 be a poor choice? Granted not great but why would we say a poor choice?

Ron

Ron_Blain:
@Leo
Why would the ADS1115 be a poor choice? Granted not great but why would we say a poor choice?

Ron

I added "absolute" and "ratiometric" as hints.

Load cell output voltage depends on two things: load and excitation (supply) voltage.
ADS output only depends on one thing: input voltage.
Therefore you should also measure excitation voltage, and use it's variation to compensate results.

Much easier to use a ratiometric A/D with a ratiometric sensor.
If load cell supply and A/D reference are coming from the same point, then, when supply goes up load cell output increases, but A/D output decreases with the same ratio. Automatic compensation.

The regulated 4.3volt excitation voltage of the HX711 is also internally used as reference for it's A/D.
Leo..

Otay and thank you for sharing that. Not all but most of the load cells I worked with we used 10 volt excitation and absolutely from a stable well regulated supply and even then the cells were calibrated.

Ron

Wawa:
"It has a supply voltage of 5volt" is a wrong assumption.
Load cells don't have a fixed supply voltage. The datasheet only recommends 5volt.
The HX711 works with an excitation (load cell supply) voltage of 4.3volt, which is perfectly fine.
A HX711 board does need a 5volt supply for that,
and if you're going to use a 3.3volt processor (WeMos, ESP32 etc.), then you need a Sparkfun HX711 board with separate 5volt analogue and 3.3volt digital supply connections.

@Ron_Blain
An ADS1115 (absolute A/D) is a poor choice for a load cell (ratiometric sensor).
Leo..

Thanks for your reply and everyone else’s , they have been very helpful.
I have decided on 3 sparkfun HX177 modules for my 3 load cells. However I am not sure on the amps of the load cells are as it’s not on the data sheet and I don’t have the cells in hand. So I can calculate the power I need. I plan to supply power for 10 hours or less. What is the purpose is a lipo booster ? Can anyone help explain?
Additionally the WEMOS D1 mini ESP32 requires power through a micro USB port is there a preferred power source for the WEMOS? As the circuit is to be wireless, a power bank was suggested but is this a good power source ?? Thanks

adam272000:
I am not sure on the amps of the load cells

I wouldn't worry about that. A few mA...

A cellphone powerbank should be fine. Even a small-ish 5A type could keep it running for 24H+.
Leo..

Wawa:
I wouldn't worry about that. A few mA...

A cellphone powerbank should be fine. Even a small-ish 5A type could keep it running for 24H+.
Leo..

Great thanks. Just to confirm the power bank powers ony the modules and wemos?
The load cells still require power right? Hence my original question im struggling to decide how to power the 3 load cells in how to connect them ?

If you go with the HX711 modules they provide excitation as was covered earlier. Load cells draw, as was mentioned, a few mA of excitation current.

Ron

Ron_Blain:
If you go with the HX711 modules they provide excitation as was covered earlier. Load cells draw, as was mentioned, a few mA of excitation current.

Ron

Cheers, so just to confirm the load cells draw power from the HX177 modules. Hence the power bank connected to the WEMOS provides power through the modules to the load cells. So two sources of power aren't needed just one?

adam272000:
Cheers, so just to confirm the load cells draw power from the HX177 modules. Hence the power bank connected to the WEMOS provides power through the modules to the load cells. So two sources of power aren't needed just one?

Correct.
Just make sure you connect the analogue supply (VCC) of the HX711 to the 5volt pin of the WeMos, and the digital supply (VDD) of the HX711 to the 3.3volt pin of the WeMos.
Leo..

Wawa:
Correct.
Just make sure you connect the analogue supply (VCC) of the HX711 to the 5volt pin of the WeMos, and the digital supply (VDD) of the HX711 to the 3.3volt pin of the WeMos.
Leo..

Perfect ! I plan on using my 10000mAh portable charger which has a 5V, 2.4A output .

Wawa:
Correct.
Just make sure you connect the analogue supply (VCC) of the HX711 to the 5volt pin of the WeMos, and the digital supply (VDD) of the HX711 to the 3.3volt pin of the WeMos.
Leo..

Yes and that is important. Make sure the HX711 modules you get allow Analog and Digital supplies. The early boards (modules) didn't and you needed to cut a run on the board for dual supply use. This was also covered previously in this thread.
Ron

Ron_Blain:
Yes and that is important. Make sure the HX711 modules you get allow Analog and Digital supplies. The early boards (modules) didn't and you needed to cut a run on the board for dual supply use. This was also covered previously in this thread.
Ron

I plan to use 3 of the Sparkfun hx177 module: Load Cell Amplifier - HX711 (SEN-13879) — Cool Components
Which has an ADC, therefore, will suffice?

Your next problem with this is the HX711 is an I2C device and it has an address. I have only played around with a single unit. To the best of my knowledge you can't change the address. Unless someone else has some thoughts as how to use 3 of the HX711 modules or knows how to change the address you may want to think about a MUX (Multiplex) scheme, something along these lines.

Ron

Ron_Blain:
...the HX711 is an I2C device and it has an address.

Wrong. Not an I2C device, no address.

There is a HX711_multi library out there that allows several devices to share the clock pin, so four common digital pins are needed for three devices.
Leo..

Then he is good to go. My bad as to the I2C address.

Many Thanks for the correction.
Ron

Wawa:
Wrong. Not an I2C device, no address.

There is a HX711_multi library out there that allows several devices to share the clock pin, so four common digital pins are needed for three devices.
Leo..

Advice on how to combine the multiple analogue supplies to the 5V on the WEMOS and respectively for the multiple digital supplies?

Hi, for the HX177 to WEMOS connections I am slightly stuck! Should the DAT lines have separate digital ports and the clock lines have the same digital port? By this, I mean all currently I have designed all DAT wires from the HX177 module to connect to separate digital ports the WEMOS? and all the clock wires from the HX177 module connect to the same digital ports( or should this be same analogue port) on the WEMOS.

I aim to program using the Arduino IDE for the load cells to work individually and just output the force they experience. thanks.

Did you search for, read, and install a HX711_multi library.
All the information should be on those pages. One clock, three data lines.

The HX711 is digital.
Nothing do do with analogue, apart that some examples use analogue pins as digital, to confuse you.

Get ONE HX711 working before you expand to three.
Search for which pins you can use on a WeMos. Not all can be used.
Leo..

Wawa:
Did you search for, read, and install a HX711_multi library.
All the information should be on those pages. One clock, three data lines.

The HX711 is digital.
Nothing do do with analogue, apart that some examples use analogue pins as digital, to confuse you.

Get ONE HX711 working before you expand to three.
Search for which pins you can use on a WeMos. Not all can be used.
Leo..

Thanks. That's where I was getting confused. I understand the HX177 is digital BUT some of the examples online were confusing using analogue pins. I just want to design my circuit before I built the circuit when the components ARRIVE.
I can't test one load cell and module as I haven't built the circuit yet. I just wanted to get a full understanding of the circuit before I do. I connected the all clock pins from the HX177 to a single digital pin on the WEMOS and the data pins are connected to their own digital pins. I have understood clock lines to be the wires from the clock pins but the library or forums don't explain if these connect to a signal digital pin or another type of pin on the WEMOS?

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.