hi forum!
so i'm thinking in building a scale that shows information on Android via Bluetooth (using the MIT app inventor [0]... can i use 2 cells in the same HX711 module? i'm thinking in getting one that have a precision of 100 grams and another one of 1 Kg!
if yes or no, can i use both cells at the same Nano or am i over judging its processing power?
The HX711 Module (Fig-1) has two ADC Channels (Channel-A and Channel-B); so, we will be able to connect two wheatstone-type Load Cells. NANO is powerfull enough to process your data.
Figure-1:
Which Nano.
The board pictured in post#2 can only be used with a classic Atmega328 board.
Newer 3.3volt-logic Nanos (with bluetooth) need a different version of that HX711 board.
Connecting several HX711 boards to a Nano is not a problem.
There is even a HX711-Multi library for that.
Leo..
Atmega328P, 5v
Data sheets of HX711 show that the device/module can be operated from 2.5V to 5.5V.
Therefore , the Board of Fig-2 can be connected with 3.3V MCU when VCC-pin of the HX711 Module is tied with 3.3V.
That's the voltage range of the HX711 chip, not for the board it's mounted on.
Some parts on the board need a 5volt supply.
The board has a 4.3volt voltage regulator for the load cell that needs at least 4.6volt to do it's job.
@OP. Yes, any HX711 board can be used with a 5volt-logic 328.
Leo..
There is a DVDD supply pin, to power the digital parts of the chip, which should get the processor's logic voltage (5volt or 3.3volt). So there is no need for logic level shifting.
And there is a VSUP pin, for the that "analogue supply regulator" block. Supply voltage for that part of the chip depends on the two feedback resistors R1,R2.
Those resistors set the voltage for the AVDD pin, and power for the load cell. The resistor values are calculated for an AVDD voltage of 4.3volt. It should be clear that you can't get that voltage if the S8550 pass transistor is powered with less than ~4.6volt.
The HX711 module from Sparkfun has separate connectors for the digital and analogue blocks,
VDD for the digital part and VCC for analogue part of the board. Link in post#3.
Making it the only board I know that's suitable for 3.3volt-logic processors.
Leo..
so, i could only get the schematic of one of the sensors (they didn't arrive & i'll post their dimensions later on) but i'm now wondering what to-do with the design! should the small scale be located at the top of the bigger module? not touching it, of course... or should i let them spaced as the picture & in the space in-between i add a Nano holder?
edit: by "on top of the bigger module i meant something like this;
you could simplify the system by moving to a microcontroller with onboard Bluetooth and dumping the HC-06, e.g. an ESP32 which has onboard WiF, Bluetooth Classic and BLE
there's much programming difference? i'm not seasoned in programming much, so what i'll do here is a soup of tutorials i found over the internet...
anyway, tha Nano is already on my way
totally different
theHC-06 is a seperate module connected via serial communication and sent commands
the ESP32 executes Bluetooth library code onboard
lets see how this projects evolves (i'm a bit skeptical of the precision i'll get from > 5 USD weight modules)... maybe we can do an ESP32 later?
supp!
the plate supports are printing, but i got this so far;
so, i was reading about scale.set_gain(x) as we'll use it for accessing the A and B input from HX711, does it makes sense wiring the 100.g instead of the 1.kg sensor at A as it has a higher gain? or does it have no noticeable difference?
also we need to change the structure for an unified one... but i was just testing my Blender CAD skills 
and my 1° exp. with 3D printing!
the .stl files are a modified version of: USB C Arduino Nano Slim Case by ShafinM - Thingiverse and Load cell testbed by RRacer - Thingiverse (when i find time i'll add their licenses to the .zip file, as well all the measures used)
well, i still have no idea what to do with the design! i'll use this thing for a while and in case no one drafts anything, i'll probably do a support single mesh... about the code; i couldn't make it work with both scales running at the same time (we need to use the button toggle and re-calibrate every-time)! apparently data gets mixed and i have no idea what to do (already tried to set high delays but no avail); keep in mind that i set the calibration weight in both sensors to 50 grams as i didn't left my bedroom to search for something with 700 grams for the 1.kg bit 
there are some stuff to do before i post the .stls and .ino! from calculating the weight of the overload message, correctly (so far i'm not considering the tared one); increase the plates a bit so dirt don't get inside the mesh and correcting some holes sizes for screws...
edit: 
yeah! using the scale through bluetooth and a touchscreen was too messy and clunk! i also added one more board for getting the data of one of the cells, as my skills and what i read from Github, it's too slow and messy to make both work from one board only...
