i also try to connect two hx711 boards to an esp32 devkit v1.
I connected 1 to pin 18&5, that one is working.
but I have no idea where I can connect the second one to.

 

Hi Edi,
Welcome to AAC.
Please post a circuit diagram and your Sketch.
E

 

i also try to connect two hx711 boards to an esp32 devkit v1.
I connected 1 to pin 18&5, that one is working.
but I have no idea where I can connect the second one to.

 

View attachment 269359

thank you for the quick reply.
maybe a dumb question, as that I connect one board to pin 18&5 (that is working).
Do I need to connect the other one to pin 15&14?
Iam totally new to this but eager to learn.

 

could not edit my last post but I tried the 23&19 , 15&14 but I get no value's.
correct me if i'am wrong but I can connect the wires to the pins and assign them the function, so can connect the wires how I want?
iam still in the calibratie modus and using the sketch like in the link below.
https://github.com/EverythingSmartHome/mqtt-bed-sensor/tree/master/Scale_Calibration

 

Hi Edi,
Welcome to AAC.
Please post a circuit diagram and your Sketch.
E

Hi Eric,

thank you for the warm welcome.

I use the calibration sketch in the following link:
https://github.com/EverythingSmartHome/mqtt-bed-sensor/tree/master/Scale_Calibration

i connect the dt->pin5
sck->pin18
the board gets its 5v from the esp32
this one is working.

With the second one I tried different pins and its not working: dt->19. dt->15
sck->23. sck->14
i 'am calibration them separately (one board at the time)

 

Looking at the HX711_basic_example.ino it seems that the HX711 library creates an object to simplify communications.

I would suggest trying to create two such objects with suitable pins pairs for each load cell sensor. Any unused GPIO pins should be suitable.

#include "HX711.h"

const int LOADCELL_1_DOUT_PIN = 2;
const int LOADCELL-1_SCK_PIN = 3;

const int LOADCELL_2_DOUT_PIN = 4;
const int LOADCELL_2_SCK_PIN = 5;

void setup() {
  scale_1.begin(LOADCELL_1_DOUT_PIN, LOADCELL_2_SCK_PIN);
  scale_2.begin(LOADCELL_2_DOUT_PIN, LOADCELL_2_SCK_PIN);

  Serial.begin(57600);
}

void loop() {
    long reading = scale_1.read();
    Serial.print("HX711_1 reading: ");
    Serial.println(reading);

    reading = scale_2.read();
    Serial.print("HX711_2 reading: ");
    Serial.println(reading);
}

 

Looking at the HX711_basic_example.ino it seems that the HX711 library creates an object to simplify communications.

I would suggest trying to create two such objects with suitable pins pairs for each load cell sensor. Any unused GPIO pins should be suitable.

#include "HX711.h"

const int LOADCELL_1_DOUT_PIN = 2;
const int LOADCELL-1_SCK_PIN = 3;

const int LOADCELL_2_DOUT_PIN = 4;
const int LOADCELL_2_SCK_PIN = 5;

void setup() {
  scale_1.begin(LOADCELL_1_DOUT_PIN, LOADCELL_2_SCK_PIN);
  scale_2.begin(LOADCELL_2_DOUT_PIN, LOADCELL_2_SCK_PIN);

  Serial.begin(57600);
}

void loop() {
    long reading = scale_1.read();
    Serial.print("HX711_1 reading: ");
    Serial.println(reading);

    reading = scale_2.read();
    Serial.print("HX711_2 reading: ");
    Serial.println(reading);
}

thank you for the reply, I will try to adopt this code once I can get a reading from the second loadcell.

Within the calibration sketch I put :
const int LOADCELL_DOUT_PIN = 19;
const int LOADCELL_SCK_PIN = 23;

but I get a zero value despite I put weight on it or not.
i wired the second loadcell the same as the first one, the first one I put on:
const int LOADCELL_DOUT_PIN = 5;
const int LOADCELL_SCK_PIN = 18;

 

Hi Edi,
post your Sketch when ready, I have a two HX711project set up on the bench, I can check your code.
Which type load cells are you using.?
E

 

Hi Eric,

I use the the filling calibration sketch:

#include <HX711.h>

HX711 scale;  // Initializes library functions.

const int LOADCELL_DOUT_PIN = 19;          //Remember these are ESP GPIO pins, these might not be the pins labeled on the board.
const int LOADCELL_SCK_PIN = 23;

int calibration_factor = 2400; // Defines calibration factor we'll use for calibrating.

void setup()
{
  Serial.begin(74880);   // Starts serial communication in 9600 baud rate.

  Serial.println("Initializing scale calibration.");  // Prints user commands.
  Serial.println("Please remove all weight from scale.");
  Serial.println("Place known weights on scale one by one.");


  scale.begin(LOADCELL_DOUT_PIN, LOADCELL_SCK_PIN);   // Initializes the scaling process.
  scale.set_scale();
  scale.tare();          // Resets the scale to 0.
}


void loop()
{

  scale.set_scale(calibration_factor);  // Adjusts the calibration factor.
  scale.wait_ready();
  Serial.print("Reading: ");            // Prints weight readings in .2 decimal kg units.
  Serial.print(scale.get_units(), 2);
  Serial.println(" kg");
  Serial.print("Calibration factor: "); // Prints calibration factor.
  Serial.println(calibration_factor);

  scale.power_down();    // Puts the scale to sleep mode for 3 seconds.
  delay(3000);
  scale.power_up();
}

the following code I wanne use for the final readout with two sensors:

#include <Arduino.h>
#include <HX711.h>
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include "config.h"

HX711 scale;                          // Initiate HX711 library
WiFiClient wifiClient;                // Initiate WiFi library
PubSubClient client(wifiClient);      // Initiate PubSubClient library

void setup() {
  Serial.begin(74880);
  Serial.println();
  WiFi.mode(WIFI_STA);
  WiFi.begin(SSID, PASSWORD);
  Serial.print("Connecting...");

  while (WiFi.status() != WL_CONNECTED) {       // Wait till Wifi connected
    delay(500);
    Serial.print(".");
  }
  Serial.println();

  Serial.print("Connected, IP address: ");
  Serial.println(WiFi.localIP());                     // Print IP address

  client.setServer(MQTT_SERVER, 1883);                // Set MQTT server and port number
  client.setCallback(callback);                       // Set callback address, this is used for remote tare
  scale.begin(LOADCELL_DOUT_PIN, LOADCELL_SCK_PIN);   // Start scale on specified pins
  scale.wait_ready();                                 //Ensure scale is ready, this is a blocking function
  scale.set_scale();                                 
  Serial.println("Scale Set");
  scale.wait_ready();
  scale.tare();                                       // Tare scale on startup
  scale.wait_ready();
  Serial.println("Scale Zeroed");
}

void loop() {
  float reading; // Float for reading
  float raw; // Float for raw value which can be useful
  scale.wait_ready(); // Wait till scale is ready, this is blocking if your hardware is not connected properly.
  scale.set_scale(calibration_factor);  // Sets the calibration factor.

  // Ensure we are still connected to MQTT Topics
  if (!client.connected()) {
    reconnect();
  }
 
  Serial.print("Reading: ");            // Prints weight readings in .2 decimal kg units.
  scale.wait_ready();
  reading = scale.get_units(10);        //Read scale in g/Kg
  raw = scale.read_average(5);          //Read raw value from scale too
  Serial.print(reading, 2);
  Serial.println(" kg");
  Serial.print("Raw: ");
  Serial.println(raw);
  Serial.print("Calibration factor: "); // Prints calibration factor.
  Serial.println(calibration_factor);

  if (reading < 0) {
    reading = 0.00;     //Sets reading to 0 if it is a negative value, sometimes loadcells will drift into slightly negative values
  }

  String value_str = String(reading);
  String value_raw_str = String(raw);
  client.publish(STATE_TOPIC, (char *)value_str.c_str());               // Publish weight to the STATE topic
  client.publish(STATE_RAW_TOPIC, (char *)value_raw_str.c_str());       // Publish raw value to the RAW topic

  client.loop();          // MQTT task loop
  scale.power_down();    // Puts the scale to sleep mode for 3 seconds. I had issues getting readings if I did not do this
  delay(3000);
  scale.power_up();
}

void reconnect() {
  while (!client.connected()) {       // Loop until connected to MQTT server
    Serial.print("Attempting MQTT connection...");
    if (client.connect(HOSTNAME, mqtt_username, mqtt_password, AVAILABILITY_TOPIC, 2, true, "offline")) {       //Connect to MQTT server
      Serial.println("connected");
      client.publish(AVAILABILITY_TOPIC, "online", true);         // Once connected, publish online to the availability topic
      client.subscribe(TARE_TOPIC);       //Subscribe to tare topic for remote tare
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      delay(5000);  // Will attempt connection again in 5 seconds
    }
  }
}

void callback(char* topic, byte* payload, unsigned int length) {
  if (strcmp(topic, TARE_TOPIC) == 0) {
    Serial.println("starting tare...");
    scale.wait_ready();
    scale.set_scale();
    scale.tare();       //Reset scale to zero
    Serial.println("Scale reset to zero");
  }
}

I checkend everything again, the wiring,code and voltages at the hx711 board.
I found that between the vcc and grnd is around 5v, but at the sensor side between the E+ and the E- I don't measure anything.
So I think I broke my hx711 board, I ordered a new one to change it out and try again.
The load cells iam using are P.S.D modelsd-s1 200kg.

 

hi Edi,
Downloaded your files, will run them, let you know how it goes.
E

 

hi Edi,
Where did you get the first Sketch from.?
When running, the Vext to the Load Cell is being pulled from ~+4v to almost 0v, during a Read cycle.

Do you have a photo of your ESP32 so that I can check the pin coding agrees.

E

 

hi Edi,
Where did you get the first Sketch from.?
When running, the Vext to the Load Cell is being pulled from ~+4v to almost 0v, during a Read cycle.

Do you have a photo of your ESP32 so that I can check the pin coding agrees.

E

I found the sketches at the following link:
https://github.com/EverythingSmartHome/mqtt-bed-sensor

Could the voltage drop be because of the de 3 sec delay that the loadcell turns off?

I use the esp32-wroom-da module library.
I use the following esp32 board:

 

hi Edi,
I had a wiring problem on my board, will continue testing.
E
My module layout a little different to yours.

 

hi Edi,
I had a wiring problem on my board, will continue testing.
E
My module layout a little different to yours.

yes I found also different esp32 layouts, that was adding to the confusing.
Thank you so much for your time

 

hi Edi,
Which version of the HX711 Lib are you using.?
Could you post a short listing of the results you got when using the 'working' first program.?

E

 

hi Edi,
Which version of the HX711 Lib are you using.?
Could you post a short listing of the results you got when using the 'working' first program.?

E

Hi Eric,
the lib version I use is 0.7.4 by Bogdan Necula.
I found out that one board was't outputting 5v to the loadcell.
I changed that board out for a new one from sparkfun, so I loaded the calibration sketch and the second one is working.
So now I have two working loadcells with a deviation of 0.02, that is accurate enough.
Now I only have to see if I can combine the two of them in one sketch and push the values using Mqtt to my home assistant.

 

hi Edi,
Also using Bogdan.
I have two load cells I use for testing, 5kG and 30kG.
The 30kG was giving weird results, check the cable, and it had been chewed up by a mouse or some other critter... its ruined.!
However, the 5kg is running OK, see the clip attached. 500gm Cal weight and 36gm weight.
I will knock up a resistive test box to substitute for the ruined load cell.

Keep me posted with your dual sketch and I will run it.

E

 

hi Edi,
There is a problem with that ESP32/Bogdan library, in that if the unloaded load cell output is greater than ~ -100uV the set-up code fails and the readings are large negative values.
I encountered this problem when using the 30kG load cell on the ESP32 , HX711 & Bogdan sketch, fixed it by adding a small positive offset voltage on the HX711 A+ input [1meg to +Vx].
When using the 30kG L/C with a Uno code and library, it works OK.

E

 

Hello Eric,

due to some really nice weather here in holland my reply is a bit late, sorry for that.

I finished connected the sales under my bed and sinds I use home assistant I decided to use the esphome add-on and found a
piece off code to use and well it works flawless, only have to fine tune it a bit.
Thank you for your time and patience.

I don't think this piece off code works with the ardunio software but here it is:

globals:
  - id: initial_zero
    type: float
    restore_value: yes
    # NOTE: make sure to align this value to the one used in "calibrate_linear" below!
    initial_value: '51265'
  - id: initial1_zero
    type: float
    restore_value: yes
    # NOTE: make sure to align this value to the one used in "calibrate_linear" below!
    initial_value: '8037'
    
  - id: auto_tare_enabled
    type: bool
    restore_value: yes
    initial_value: 'true'
  - id: auto_tare1_enabled
    type: bool
    restore_value: yes
    initial_value: 'true'

  - id: auto_tare_difference
    type: float
    restore_value: yes
    initial_value: '0'
  - id: auto_tare1_difference
    type: float
    restore_value: yes
    initial_value: '0'
    
  - id: manual_tare_flag
    type: bool
    restore_value: no
    initial_value: 'false'
  - id: manual_tare1_flag
    type: bool
    restore_value: no
    initial_value: 'false'

    
switch:
  ## Switch to enable/disable the auto tare feature
  - platform: template
    id: bed_deur_continuous_tare_enabled
    name: "Smart Scale Continuous Tare Enabled"
    lambda: |-
      return id(auto_tare_enabled);
    turn_on_action:
      - lambda: |-
          id(auto_tare_enabled) = true;
    turn_off_action:
      - lambda: |-
          id(auto_tare_enabled) = false;
          
  - platform: template
    id: bed_kast_continuous_tare_enabled
    name: "Smart Scale Continuous Tare Enabled"
    lambda: |-
      return id(auto_tare1_enabled);
    turn_on_action:
      - lambda: |-
          id(auto_tare1_enabled) = true;
    turn_off_action:
      - lambda: |-
          id(auto_tare1_enabled) = false;
 
  ## Switch used to initiate a manual tare
  - platform: template
    id: bed_deur_manual_tare_action_switch
    name: "Smart Scale Manual Tare Action"
    lambda: |-
      return id(manual_tare_flag);
    turn_on_action:
      - lambda: |-
          id(auto_tare_difference) = id(initial_zero) - id(bed_deur_value_raw).state;
      - switch.turn_off: bed_deur_manual_tare_action_switch
    turn_off_action:
      - lambda: |-
          id(manual_tare_flag) = false;
  - platform: template
    id: bed_kast_manual_tare_action_switch
    name: "Smart Scale Manual Tare Action"
    lambda: |-
      return id(manual_tare1_flag);
    turn_on_action:
      - lambda: |-
          id(auto_tare1_difference) = id(initial1_zero) - id(bed_kast_value_raw).state;
      - switch.turn_off: bed_kast_manual_tare_action_switch
    turn_off_action:
      - lambda: |-
          id(manual_tare1_flag) = false;

## Sensor Configuration ##
sensor:
  # template sensors from global variables
 
  - platform: template
    id: bed_deur_initial_zero
    name: "bed deur Initial Zero"
    lambda: |-
      return id(initial_zero);
    update_interval: 1s
  - platform: template
    id: bed_kast_initial_zero
    name: "bed kast Initial Zero"
    lambda: |-
      return id(initial1_zero);
    update_interval: 1s
    
  - platform: template
    id: bed_deur_auto_tare_difference
    name: "bed deur Auto Tare Difference"
    lambda: |-
      return id(auto_tare_difference);
    update_interval: 1s
  - platform: template
    id: bed_kast_auto_tare_difference
    name: "bed kast Auto Tare Difference"
    lambda: |-
      return id(auto_tare1_difference);
    update_interval: 1s
    
  # sensors imported from home assistant
  - platform: homeassistant
    id: homeassistant_initial_zero
    entity_id: input_number.bed_deur_initial_zero
    on_value:
      then:
        - lambda: |-
            id(initial_zero) = x;
  - platform: homeassistant
    id: homeassistant_initial_zero1
    entity_id: input_number.bed_kast_initial_zero
    on_value:
      then:
        - lambda: |-
            id(initial1_zero) = x;
 
  # RAW Scale input
  - platform: hx711
    id: bed_deur_value_raw
    internal: True
    dout_pin: 5
    clk_pin: 18
    gain: 128
    unit_of_measurement: kg
    accuracy_decimals: 2
    update_interval: 0.2s
    filters:
      - sliding_window_moving_average:
          window_size: 5
          send_every: 5
    on_value:
      then:
        - sensor.template.publish:
            id: bed_deur_value
            state: !lambda 'return id(bed_deur_value_raw).state;'
        - if:
            condition:
              and:
                - lambda: 'return id(auto_tare_enabled);'
                # current smart scale value is below approx. 10KG (raw value -275743) aka nobody is standing on the scale
                - lambda: 'return id(bed_deur_value).state < 10.0;'
            then:
              - if:
                  condition:
                    # current raw scale value is below expected zero value
                    - lambda: 'return id(bed_deur_value_raw).state < (id(initial_zero) - id(auto_tare_difference));'
                  then:
                    # INcrease Auto-Tare offset to slowly align real zero value with expected zero value
                    - lambda: |-
                        id(auto_tare_difference) += 10;
                  else:
                    # DEcrease Auto-Tare offset to slowly align real zero value with expected zero value
                    - lambda: |-
                        id(auto_tare_difference) -= 10;
  - platform: hx711
    id: bed_kast_value_raw
    internal: True
    dout_pin: 23
    clk_pin: 19
    gain: 128
    unit_of_measurement: kg
    accuracy_decimals: 2
    update_interval: 0.2s
    filters:
      - sliding_window_moving_average:
          window_size: 5
          send_every: 5
    on_value:
      then:
        - sensor.template.publish:
            id: bed_kast_value
            state: !lambda 'return id(bed_kast_value_raw).state;'
        - if:
            condition:
              and:
                - lambda: 'return id(auto_tare1_enabled);'
                # current smart scale value is below approx. 10KG (raw value -275743) aka nobody is standing on the scale
                - lambda: 'return id(bed_kast_value).state < 10.0;'
            then:
              - if:
                  condition:
                    # current raw scale value is below expected zero value
                    - lambda: 'return id(bed_kast_value_raw).state < (id(initial1_zero) - id(auto_tare1_difference));'
                  then:
                    # INcrease Auto-Tare offset to slowly align real zero value with expected zero value
                    - lambda: |-
                        id(auto_tare1_difference) += 10;
                  else:
                    # DEcrease Auto-Tare offset to slowly align real zero value with expected zero value
                    - lambda: |-
                        id(auto_tare1_difference) -= 10;

    
  # Mapped value to KG
  - platform: template
    id: bed_deur_value
    name: "bed_deur"
    internal: False
    filters:
      # apply auto_tare difference
      - lambda: 'return x + id(auto_tare_difference);'
      # apply rough calibration
      - calibrate_linear:
          # retrieve these values by evaluating the raw values with loads of known mass.
          # note that a bigger difference between measurements usually results in higher resolution,
          # so measure 0 Kg and the highest known mass you have (like f.ex. your own weight, measured by a normal scale with good accuracy)
          - 51265 -> 0
          - 88682 -> 82
      # map values below 0.1 to 0 (to decrease value changes due to random fluctuation)
      - lambda: |-
          if (x <= 0.1) {
            return 0.0;
          } else {
            return x;
          }
  - platform: template
    id: bed_kast_value
    name: "bed_kast"
    internal: False
    filters:
      # apply auto_tare difference
      - lambda: 'return x + id(auto_tare1_difference);'
      # apply rough calibration
      - calibrate_linear:
          # retrieve these values by evaluating the raw values with loads of known mass.
          # note that a bigger difference between measurements usually results in higher resolution,
          # so measure 0 Kg and the highest known mass you have (like f.ex. your own weight, measured by a normal scale with good accuracy)
          - 8037 -> 0
          - 24646 -> 82
      # map values below 0.1 to 0 (to decrease value changes due to random fluctuation)
      - lambda: |-
          if (x <= 0.1) {
            return 0.0;
          } else {
            return x;
          }
          
    unit_of_measurement: kg
    accuracy_decimals: 2
    update_interval: 1.0s