How to configure tds + dallas + d1_mini

ESPHome
,
1

I am having trouble getting a proper TDS value using a TDS meter v1.0. I have found multiple articles online about this, but none seem to have the same issue I am seeing. Any help would be much appreciated.

Also, I am really not totally understanding what values I should be getting back from the sensor as raw data. I am seeing a value between 0 and 1, but I am not sure whether multiplying it by 3.3 is needed.

Here is my yaml example:

    esp8266:
      board: d1_mini

    one_wire:
      - platform: gpio
        pin: D1
        id: bus1

    sensor:
      - platform: dallas_temp
        name: temperature
        id: temperature
        update_interval: 5s
        one_wire_id: bus1
        unit_of_measurement: "°C"

      - platform: adc
        name: tds
        update_interval: 5s
        accuracy_decimals: 3
        pin: A0
        unit_of_measurement: ppm
        filters:
          - multiply: 3.3
          - lambda: return x/(1+(0.2 * (id(temperature).state-25.0)));
          - lambda: return (133.42*x*x*x - 255.86*x*x + 857.39*x)*0.5;

here is some output from the logs:

    [23:33:08][D][dallas.temp.sensor:054]: 'temperature': Got Temperature=16.4°C
    [23:33:08][D][sensor:103]: 'temperature': Sending state 16.43750 °C with 1 decimals of accuracy
    [23:33:09][D][sensor:103]: 'tds': Sending state -4995.80566 ppm with 3 decimals of accuracy
    [23:33:13][D][dallas.temp.sensor:054]: 'temperature': Got Temperature=16.4°C
    [23:33:13][D][sensor:103]: 'temperature': Sending state 16.43750 °C with 1 decimals of accuracy
    [23:33:14][D][sensor:103]: 'tds': Sending state -5011.00000 ppm with 3 decimals of accuracy
    [23:33:18][D][dallas.temp.sensor:054]: 'temperature': Got Temperature=16.4°C
    [23:33:18][D][sensor:103]: 'temperature': Sending state 16.43750 °C with 1 decimals of accuracy
    [23:33:19][D][sensor:103]: 'tds': Sending state -5011.00000 ppm with 3 decimals of accuracy
    [23:33:23][D][dallas.temp.sensor:054]: 'temperature': Got Temperature=16.4°C
    [23:33:23][D][sensor:103]: 'temperature': Sending state 16.43750 °C with 1 decimals of accuracy
    [23:33:24][D][sensor:103]: 'tds': Sending state -5011.00000 ppm with 3 decimals of accuracy
2

On esphome, ADC component prints the voltage seen by the chip, 0-1V in case of Esp8266. D1-mini has voltage divider on-board boosting the range to 3.3V so yes, you need to multiply the voltage by 3.3.

Also you likely want to take more than just one sample. Add
samples: 30 #or whatever you like
to your ADC config.

Also, double check all your calculations on lambdas:

that leads to quite big compensation, maybe you need 0.02?

1 Like
3

Final thought, I was trying to figure out how to calibrate the sensor and found that a k value should be entered, but I am not sure if I am putting this value in the right place:

      filters:
          - multiply: 3.3 # 3.3v from 0-1
          - lambda: return x/(1.0+(0.02 * (id(temperature).state-25.0))); # temp adjustment
          - multiply: 1.8 # k value calibration
          - lambda: return ((133.42 * x * x * x) - (255.86 * x * x) + (857.39 * x)) * 0.5; # v to tds conversion
          - lambda: return x/500; # convert from ppm to EC
4

From where did you find that?

5

I found the process on the wiki page: Analog TDS Sensor Meter for Arduino / ESP32 / Raspberry Pi - DFRobot Wiki

6

GravityTDS library calibration code applies it like this:

void GravityTDS::update()
{
	this->analogValue = analogRead(this->pin);
	this->voltage = this->analogValue/this->adcRange*this->aref;
	this->ecValue=(133.42*this->voltage*this->voltage*this->voltage - 255.86*this->voltage*this->voltage + 857.39*this->voltage)*this->kValue;
	this->ecValue25  =  this->ecValue / (1.0+0.02*(this->temperature-25.0));  //temperature compensation
	this->tdsValue = ecValue25 * TdsFactor;

Where TdsFactor is 0.5

7

So I should multiply the initial ec value returned, before the 3.3 (v fix) multiplier?

8

3.3 multiplier has to be always first.
For the rest, I’m not so sure. The calibration method is confusing and looks like they swapped the order EC/ temp correction.
And factor 1.8 sounds really high.

9

Would it make sense to grab the raw value from the sensor and then calculate EC using the code you shared?

Sadly, I am not sure what adcRange or aref should be.

10

After re-reading the wiki page linked above and this discussion, I believe this is the correct way to set up the sensor with a calibration k value:

     - platform: adc
      update_interval: 5s
      name: tds
      accuracy_decimals: 3
      samples: 30
      sampling_mode: avg
      pin: A0
      unit_of_measurement: ppm
      filters:
          - multiply: 3.3 # 3.3v from 0-1 (esp8266)
          - lambda: return x/(1.0+(0.02 * (id(temperature).state-25.0))); # temp adjustment
          - lambda: return ((133.42 * x * x * x) - (255.86 * x * x) + (857.39 * x)) * 0.5; # v to tds conversion
          - multiply: 0.85 # k value calibration
11

But according to the library that gave you k=1.8, it should go like this:

- multiply: 3.3 # 3.3v from 0-1 (esp8266)

- lambda: return ((133.42 * x * x * x) - (255.86 * x * x) + (857.39 * x)) * 1.8; #kValue here
- lambda: return x/(1.0+(0.02 * (id(temperature).state-25.0))); # temp adjustment 
- lambda: return x * 0.5; #TdsFactor 0.5