Use a custom sensor configuration

What this example shows

The customConfig example builds its own sensorType, SENSOR_CUSTOM, instead of using one of the library's presets, creates the sensor with it at the library's default address, 0x49, and prints the gas concentration in PPM every 2.5 seconds.

This is how you give the library this board's cell. As written, SENSOR_CUSTOM holds an example sensitivity of 100 nA per ppm, so its readings are not H2S values. For this board's SGX-4H2S-300 cell, set the values to those of the library's SENSOR_H2S preset, with the output signal the SGX-4H2S-300's datasheet gives, 460 nA per ppm (460 ± 140), in place of the preset's 1200. The preset is written for the SGX-4H2S-100 cell, and with this board's cell it reads about 2.6 times too low:

Field	Value for this board
`nanoAmperesPerPPM`	`460.0F`
`internalZeroCalibration`	`0`
`adsGain`	`ADS_GAIN_4_096V`
`TIA_GAIN_IN_KOHMS`	`TIA_GAIN_7_KOHM`
`RLOAD`	`RLOAD_10_OHM`
`REF_SOURCE`	`REF_EXTERNAL`
`INTERNAL_ZERO`	`INTERNAL_ZERO_20_PERCENT`
`BIAS_SIGN`	`BIAS_SIGN_POSITIVE`
`BIAS`	`BIAS_0_PERCENT`
`FET_SHORT`	`FET_SHORT_DISABLED`
`OP_MODE`	`OP_MODE_3LEAD_AMP_CELL`

The example code

Select Board

customConfig.ino

// Include the required library
#include "Electrochemical-Gas-Sensor-SOLDERED.h"

/**
 * Here are parameters to configure for the custom sensor:
 *
 * nanoAmperesPerPPM: From the datasheet of the particular electrochemical
 * sensor, used in the calculation of PPM/PPB
 *
 * internalZeroCalibration: A fixed value which is summed to the voltage
 * measured by the ADS. The value here should make the reading be
 * just barely 0 PPM when the sensor is in a place with none of the target gas
 *
 * adsGain: The gain of the ADS
 * The voltage here represents the max range which it can measure
 * ADS_GAIN_6_144V              6.144 V
 * ADS_GAIN_4_096V              4.096 V
 * ADS_GAIN_2_048V              2.048 V
 * ADS_GAIN_1_024V              1.024 V
 * ADS_GAIN_0_512V              0.512 V
 * ADS_GAIN_0_256V              0.256 V
 *
 * TIA_GAIN_IN_KOHMS: The gain of the amplifier
 * This increases the sensitivity of the measurement
 * TIA_GAIN_EXTERNAL            External resistance
 * TIA_GAIN_2_75_KOHM           2.75 kOhm
 * TIA_GAIN_3_5_KOHM            3.5 kOhm
 * TIA_GAIN_7_KOHM              7 kOhm
 * TIA_GAIN_14_KOHM             14 kOhm
 * TIA_GAIN_35_KOHM             35 kOhm
 * TIA_GAIN_120_KOHM            120 kOhm
 * TIA_GAIN_350_KOHM            350 kOhm
 *
 * RLOAD: The load resistor in the LMP91000
 * Specified in the electrochemical sensor's datasheet
 * RLOAD_10_OHM                 10 Ohm
 * RLOAD_33_OHM                 33 Ohm
 * RLOAD_50_OHM                 50 Ohm
 * RLOAD_100_OHM                100 Ohm
 *
 * REF_SOURCE: Source of the control voltage reference
 * For our breakout, use external, there's a 2.5V external
 * reference voltage
 * REF_INTERNAL                 Internal
 * REF_EXTERNAL                 External
 *
 * INTERNAL_ZERO: Internal zero selection
 * If the electrochemical sensor has a positive polarity, you
 * would usually want to use 20% for the most headroom in the signal
 * INTERNAL_ZERO_20_PERCENT             20%
 * INTERNAL_ZERO_50_PERCENT             50%
 * INTERNAL_ZERO_67_PERCENT             67%
 * INTERNAL_ZERO_BYPASSED               Internal zero bypassed
 *
 * BIAS_SIGN: The polarity of the bias voltage
 * BIAS_SIGN_NEGATIVE           Negative
 * BIAS_SIGN_POSITIVE           Positive
 *
 * BIAS: Added bias, percentage of the reference voltage
 * Most sensors don't require this, check each sensor's datasheet
 * BIAS_0_PERCENT               0%
 * BIAS_1_PERCENT               1%
 * BIAS_2_PERCENT               2%
 * BIAS_4_PERCENT               4%
 * BIAS_6_PERCENT               6%
 * ...
 * BIAS_22_PERCENT              22%
 * BIAS_24_PERCENT              24%
 *
 * FET_SHORT: Short the FET
 * Used to perserve the electrochemical sensor
 * Has to be disabled for the sensor to be operable
 * FET_SHORT_DISABLED           Disabled
 * FET_SHORT_ENABLED            Enabled
 *
 * OP_MODE: Mode of operation
 * OP_MODE_DEEP_SLEEP               Deep Sleep (default)
 * OP_MODE_2LEAD_GROUND_CELL        2-lead ground referred galvanic cell
 * OP_MODE_STANDBY                  Standby
 * OP_MODE_3LEAD_AMP_CELL           3-lead amperometric cell
 * OP_MODE_TEMPERATURE_TIA_OFF      Temperature measurement (TIA Off)
 * OP_MODE_TEMPERATURE_TIA_ON       Temperature measurement (TIA On)
 *
 * For more details, check thge LMP91000 datasheet, chapter 7.6
 */

// Here is an example of a custom configuration:
const sensorType SENSOR_CUSTOM = {
    100.0F,                   // nanoAmperesPerPPM
    0,                        // internalZeroCalibration
    ADS_GAIN_4_096V,          // adsGain
    TIA_GAIN_120_KOHM,        // TIA_GAIN_IN_KOHMS
    RLOAD_10_OHM,             // RLOAD
    REF_EXTERNAL,             // REF_SOURCE
    INTERNAL_ZERO_20_PERCENT, // INTERNAL_ZERO
    BIAS_SIGN_NEGATIVE,       // BIAS_SIGN
    BIAS_0_PERCENT,           // BIAS
    FET_SHORT_DISABLED,       // FET_SHORT
    OP_MODE_3LEAD_AMP_CELL,   // OP_MODE
};

// Create the sensor object with the custom type
ElectrochemicalGasSensor sensor(SENSOR_CUSTOM);

void setup()
{
    Serial.begin(115200); // For debugging

    // Init the breakout
    if (!sensor.begin())
    {
        // Can't init? Notify the user and go to infinite loop
        Serial.println("ERROR: Can't init the sensor! Check connections!");
        while (true)
            delay(100);
    }

    Serial.println("Sensor initialized successfully!");
}

void loop()
{
    // Make the reading
    double reading = sensor.getPPM();

    // Print the reading with 5 digits of precision
    Serial.println("Sensor reading: ");
    Serial.print(reading, 5);
    Serial.println(" PPM");

    // Wait a bit before reading again
    delay(2500);
}

Expected result:

Serial MonitorAutoscrollShow timestampNewline115200 baud

Message (Enter to send message to the board)

Sensor initialized successfully!

Then, every 2.5 seconds, the sketch prints Sensor reading: on one line and the concentration in PPM to five decimals, followed by PPM, on the next. If the sensor does not answer, the sketch prints ERROR: Can't init the sensor! Check connections! and stops.

Functions used

sensorType is the structure that holds one cell's settings, in this order:

Field	Type	Meaning
`nanoAmperesPerPPM`	`double`	The cell's sensitivity in nA per ppm. `getPPM()` divides by it.
`internalZeroCalibration`	`double`	Voltage added to the reading before conversion, to zero it with none of the target gas.
`adsGain`	`uint8_t`	ADC full-scale range, `ADS_GAIN_6_144V` to `ADS_GAIN_0_256V`.
`TIA_GAIN_IN_KOHMS`	`uint8_t`	Front-end amplifier gain, `TIA_GAIN_2_75_KOHM` to `TIA_GAIN_350_KOHM`, or `TIA_GAIN_EXTERNAL`.
`RLOAD`	`uint8_t`	Load resistor, `RLOAD_10_OHM` to `RLOAD_100_OHM`.
`REF_SOURCE`	`uint8_t`	Reference source, `REF_INTERNAL` or `REF_EXTERNAL`.
`INTERNAL_ZERO`	`uint8_t`	Internal zero, `INTERNAL_ZERO_20_PERCENT`, `INTERNAL_ZERO_50_PERCENT`, `INTERNAL_ZERO_67_PERCENT` or `INTERNAL_ZERO_BYPASSED`.
`BIAS_SIGN`	`uint8_t`	Bias polarity, `BIAS_SIGN_NEGATIVE` or `BIAS_SIGN_POSITIVE`.
`BIAS`	`uint8_t`	Bias as a percentage of the reference, `BIAS_0_PERCENT` to `BIAS_24_PERCENT`.
`FET_SHORT`	`uint8_t`	`FET_SHORT_DISABLED` or `FET_SHORT_ENABLED`.
`OP_MODE`	`uint8_t`	Operating mode; the presets use `OP_MODE_3LEAD_AMP_CELL`.

ElectrochemicalGasSensor(sensorType _t, uint8_t _adcAddr = DEFAULT_ADC_ADDR, int _configPin = -1)returns none

Creates the sensor object. The address decides how begin() talks to the board: an address from 0x30 to 0x37 goes through the board's ATtiny404; any other address, such as the default 0x49, goes to an ADS1115 at that address and to the LMP91000 directly.

ReturnsConstructor.

Parameters

Name	Type	Description
`_t`	`sensorType`	The configuration to use. This example passes `SENSOR_CUSTOM`.
`_adcAddr`	`uint8_t`	The address `begin()` talks to. This example leaves it out, so the default, `0x49` (`DEFAULT_ADC_ADDR`), is used.
`_configPin`	`int`	A GPIO the library holds high and pulls low while it configures the LMP91000 directly. Ignored at addresses from `0x30` to `0x37`. This example leaves it out (`-1`, none).

bool begin()returns bool

Starts I2C and picks how to talk to the board from the address. With an address from 0x30 to 0x37 it checks that the board's ATtiny404 answers and sends it the ADC gain from the configuration with the slowest data rate; each command waits up to 500 ms for an answer. With any other address it starts an ADS1115 at that address with the same gain and data rate. Either way it then writes the configuration to the LMP91000 front end. Call it once before reading.

Returnstrue when every step succeeded, false otherwise.

double getPPM()returns double

Reads the ADC, subtracts the front end's internal zero (2.5 V times its percentage), adds the zero calibration, then divides by the amplifier gain and by the configuration's sensitivity in nA per ppm. A result below 0 is returned as 0.

ReturnsGas concentration in PPM.

Putting it together

Fill in a const sensorType with your cell's values, pass it to ElectrochemicalGasSensor, call begin() once, then read with getPPM(). For this board, the first table gives the values.

SourceOpen the verified Arduino exampleView the exact source used by this page.examples/customConfig/customConfig.ino

What this example shows​

The example code​

Functions used​

Putting it together​

What this example shows

The example code

Functions used

Putting it together