Raspberry Pi Forums

Hello everybody

I'm not sure should I post this here or in the noob section, but I have serious problems with a project I'm working on. I'm trying to connect a simple 3kg load cell (4 wire type) to my RPi3.

The cell came with that simple green hx711 controller board with 8 soldering points. B+, B-,A+, A-. E+ and E-. On the other side, there are GND, DT. SCK, VCC.

I was using this tutorial (https://tutorials-raspberrypi.com/digit ... sor-hx711/) to solder everything together, and a friend who's in charge of the software part got some inconsistent readings. The scale had an accuracy level of +/-10% which is a lot for a 3 kg scale. Then I found a simple hack to connect pin 15 on the hx chip to VCC, rising the sample rate. It was still very un-accurate.

I've decided to get that brown , shielded HX711 board, but that little bugger has different markings on it: OUT+, A+, A-, GND, B+, B-. I', pretty certain that the OUT+ corresponds to E+, and GND to E-. so I've connected it that way.



The other side is also different: VCC, DO/RX, CK/TX, GND. I have connected the VCC to +5V, and GND to GND on the Rpi,

I believed that the DO equals the DT pin, and the SCK equals to CK pin.

The Rpi doesn't see the scale. As it's not connected. Then I went on and about googling for possible pin connections, and found several:

DO/Rx should be connected to GPIO28 ...which equals to DT and GPIO9
CK/Rx goes to GPIO30... and that should correspond to SCK and GPIO11

that didn't work either. GPIO 28 and 30 aren't marked on the pin layout..

I thought that the E+ or OUT+ equals to a +5V source (if the VCC pin is connected to +5V obvs), but my voltmeter doesn't measure anything. On some posts I found that the red wire from the load cell should be connected to the VCC (+5V). Tried that as well.

found another one with DO and CK connected to pins 5 and 6 if counted from the USB ports (left row, closer to the HDMI port, haven't had the time to test that version yet)

Nothing works. In the meantime, I managed to damage my SD card, loosing everything, then I corrupted a spare one I had because I stopped the IMG writing.. and finally got the 3rd working again.


To get to the point....

which is the correct wiring diagram for the brown (red?) HX 711 amplifier circuit, for the RPi3? what pin (either by official pin layout, or basic counting method) should each of the hx 711 points be connected? Same with the cell.. if the green wire is A-, and the white A+, where do I connect the red one? Out+ or the +5V (VCC pin on the other side)

you can even mark it out on the pin layout picture

https://www.jameco.com/Jameco/workshop/ ... e_fig2.jpg

please help me, because this is really frustrating.

I'm using a fivr programmer from Pakistan, so both the time and mileage difference aren't helping matters...

Vcc --- 3V3
GND --- ground
DO/DT --- any GPIO
CK/SCK --- any GPIO

E+ --- 3V3
E- --- ground

Use channel A or B according to the gain you want.

Channel A gain 64 or 128, channel B gain 32.

Ok, tried soldering DO wire to GPIO6, and CK to GPIO5

And got a glimps of an error. Managed to take a photo.. It dissappears in a second, and the terminal shuts down.

And got a glimps of an error.

What is shown on the screen is a Warning, for information, not an error that causes termination of the script.

joan wrote: ↑

Wed Jan 22, 2020 9:46 am

Vcc --- 3V3
GND --- ground
DO/DT --- any GPIO
CK/SCK --- any GPIO

E+ --- 3V3
E- --- ground

Use channel A or B according to the gain you want.

Channel A gain 64 or 128, channel B gain 32.

ok, and what about the other side.. towards the load cell? I don't have E+ or E- on the shielded controler. I have GND (E-?) and OUT+ (E+?).

do I use the OUT+ or do I solder it to the VCC pin for the red wire

and which gain gives more accurate results? weight change should be in tens of grams..

I'm googling extensively, but failing to find a straight formward answer. Everybody is using A+/- terminals, so I believe that's better.

One more thing.. why use 3V3 for the VCC? the nominal voltage for the load cell is from 5-10 Volts, where 5V is preferred... 3,3V is under the excitation level for the cell..

ChILd_ReBoRn wrote: ↑

Wed Jan 22, 2020 11:57 am

One more thing.. why use 3V3 for the VCC? the nominal voltage for the load cell is from 5-10 Volts, where 5V is preferred... 3,3V is under the excitation level for the cell..

Unless one understands 110% what one is doing, never connect any device powered from 5 volts to a RPi GPIO input. RPi GPIOs use 0 and 3.3 volt logic levels and are NOT 5 volt tolerant. It is not just a matter of getting erroneous results. Exceeding those voltage levels can damage the GPIO and even kill the whole SoC.