Hello everyone! I want to make a project where 16 HX711 scale modules will be connected to one Arduino Mega 2560. Tell me, can I have any problems with getting values from sensors with such a quantity? I assembled 4 sensors on Nano328 - everything was fine there. Now the only thing that confuses me is that I plan to use the D22-D53 connector block. Since SPI is occupied for W5500, and D2-D9 will be used for PWM. I attach the diagram.
Figma Board
Interesting project,
the HX711 array should get their own power supply(s) + GND from the MEGA to have a common reference.
You might check my library - GitHub - RobTillaart/HX711: Arduino library for HX711 24 bit ADC used for load cells and scales.
I have discussed using an array of loadcells with a shared clock pin in the past.
It has side effects but it might work for you. Would save 15 clock pins on the MEGA.
Thanks for the suggestions, I have already studied this library, but I would like to use the "Conditionally stable" version with a standard connection, since the choice already hints at Arduino Mega. My question arose solely because I read a topic about connecting via PCF8574. I found out that it cannot be used due to the I2C speed. Are there any restrictions on the speed of the MEGA2560 D22-53 pins? The power supply for each sensor is laid in the 8P8C connector (2 VCC, 4 data pins and 2 GND)
Do you have a link?
Thinking out loud,
It would indeed take 3 I2C calls per bit, one call at least 2 bytes, yes would slow communication with one or two orders of magnitude.
for performance one might use the SPI MCP23S17
With a shared clock one could read up to 7 (or 15) sensors in parallel in theory.
would take a dedicated code to work
Not that I am aware of.
Be aware that 16 HX711's can draw quite some current.
Did you do some measurements with your 4 channel setup?
In all my projects I use an AD-DC converter on PCB for 5V2A, according to my calculations this is enough for Mega2560, W5500, MOSFETs and all kinds of sensors on 8p8c ports.
Note that pin 50-53 (SPI) will be used by the W5500.
Leo..
Wow, the pinout actually shows SPI on pins 50-53, not 11-13. Does that mean the standard UNO Ethernet Shield won't work with the Mega2560?
Oh, no. Shield uses ICSP connector. Right?
Which is internally connected to those SPI pins.
Leo..
Thank you! It's very important note!
The analogue pins can also be used as digital pins.
You only need 17 digital pins for 16 Hx711 boards.
The HX711 draws very little current, but the load cells draw a bit.
A 4*350 Ohm bridge draws 4.3/350 = ~12mA. 4.3 being the regulated excitation voltage of the HX711. I calculate 70mA for the Mega, 240mA for the 16 load cells and 160mA for the W5500. That's 470mA total, and the absolute max for USB.
Leo..