Problem with Arduino, load cell and LED display

[zoran_urban]

Hi all.
I have made project with Arduino Mega 2560, load measuring cell (full bridge), load cell amplifier and LED display (block diagram attached).
In short, everything was working fine for half an hour and then suddenly power supply, step down converter and Arduino start having some sort of interruption in work, like working in cycle. Everything powers up and after half a second goes down, than again up,down... LED display freezes on last value and that’s it.
First I taught that it was power supply, but it is 1,5A, it should be sufficient for Arduino and peripherals.
Any idea what could cause this?

[Wawa]

Which buck converter, and did you connect it to the 5volt pin?
A load cell amplifier powered by 24volt and then connected to a 5volt input sounds suspicious.
Why did you use that, with the low-resolution Arduino A/D, and maybe with the instability of default 5volt Aref (we didn't see your code). Everybody else uses a 24-bit digital HX711 breakout board.
Leo..

[TomGeorge]

Hi, @zoran_urban
Welcome to the forum.

Please read the post at the start of any forum , entitled "How to use this Forum".

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Can you please post link to spec/data of the Load Cell Amplifier?
Can you please post link to Step down converter?

Do you have a DMM?
If so can you measure the voltage between the 2560 gnd and the Load Cell gnd?

Thanks.. Tom..

[zoran_urban]

Hi Leo.

Idea was to use this amplifier, because I taught it will be better solution then HX711 and not expensive in the end.

tda-01_manual.pdf (200.8 KB)

[cndg]

What load cell are you using?

All the simple ones work directly from the arduino - no 24v or other power needed.

[zoran_urban]

DC-DC Step Down regulator LM2596SHVS 4.5-60V DC
In: 4.5V-50V
Out: 3V-35V
Output current: Nominal 2A
Outpit deviation: 30mV (max)
Work frequency: 150kHz
Temp. range: -40° C do +85° C

[TomGeorge]

Hii,
Have you measured the 5V and 24V when the system is cycling?

Tom...

[Wawa]

@zoran_urban

Idea was to use this amplifier, because I taught it will be better solution then HX711

The opposite is true.
As said, the HX711 does not rely on the low 10-bit resolution of the Arduino, and on the stability of the Arduino power supply (which that 0-5volt output of the amplifier does).

With the HX711 you can also forget about the buck converter, and power the Mega (which powers the HX711) with a 5volt cellphone charger connected to the USB socket.
Leo..

[zoran_urban]

Sorry for late reply. I was out of the office for some days and couldn’t measure it. When I did it, I found out that it is cycling from 0 to around 2V. Frequency of pulsation is the same as frequency of reading pins.
Definitely bad wiring in practice.

Thanks for advice.

[zoran_urban]

Wawa,

thanks for pointing in right direction. I taught that 10 bit resolution is enough for this project and that commercially available (but cheap) amplifier is good solution. First asumption was very wrong, second one only wrong.
I have made new wiring with HX711 and except solving problem with bad wiring (99% this was the problem), measuring is now with error that can fit to normal distribution.

Thanks once again.

Zoran