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MH-Z19 sensor: disable auto-calibration and some odd fixes #592

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MH-Z19 sensor: disable auto-calibration and some odd fixes #592

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a416375
mhz19: igrnore data from sensor wile it's booting
May 5, 2019
e834bf1
mhz19: add detection of B sensor revision
May 5, 2019
df2f4da
mhz19: disable autocalibration for MH-Z19B
May 5, 2019
31bae8c
mhz19: cleanup uart RX buffer before sending command
May 5, 2019
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59 changes: 57 additions & 2 deletions src/esphome/sensor/mhz19_component.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ static const char *TAG = "sensor.mhz19";
static const uint8_t MHZ19_REQUEST_LENGTH = 8;
static const uint8_t MHZ19_RESPONSE_LENGTH = 9;
static const uint8_t MHZ19_COMMAND_GET_PPM[] = {0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00};
static const uint8_t MHZ19_COMMAND_ABC_DISABLE[] = {0xFF, 0x01, 0x79, 0x00, 0x00, 0x00, 0x00, 0x00, 0x86};

MHZ19Component::MHZ19Component(UARTComponent *parent, const std::string &co2_name, uint32_t update_interval)
: PollingComponent(update_interval), UARTDevice(parent), co2_sensor_(new MHZ19CO2Sensor(co2_name, this)) {}
Expand All @@ -26,18 +27,59 @@ uint8_t mhz19_checksum(const uint8_t *command) {

void MHZ19Component::update() {
uint8_t response[MHZ19_RESPONSE_LENGTH];
repeat:
if (!this->mhz19_write_command_(MHZ19_COMMAND_GET_PPM, response)) {
ESP_LOGW(TAG, "Reading data from MHZ19 failed!");
this->status_set_warning();
return;
}

if (response[0] != 0xFF || response[1] != 0x86) {
ESP_LOGW(TAG, "Invalid preamble from MHZ19!");
ESP_LOGW(TAG, "Invalid preamble from MHZ19! [%0x %0x %0x %0x %0x %0x %0x %0x %0x]",
response[0], response[1], response[2], response[3], response[4],
response[5], response[6], response[7], response[8]);
this->status_set_warning();
if (++this->cleanup_rx_buffer > 2) {
/* try to recover and give up on it if several attemprs were no successful until the next update cycle */
this->cleanup_rx_buffer = 0;
return;
}
goto repeat;
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}
this->cleanup_rx_buffer = 0;

/* Sensor reports U(15000) during boot, ingnore reported CO2 until it boots */
uint16_t u = (response[6] << 8) + response[7];
if (u == 15000) {
ESP_LOGD(TAG, "Sensor is booting");
return;
}

/* MH-Z19B(s == 0) and MH-Z19(s != 0) */
uint8_t s = response[5];
if (response[5] == 0 && this->model_b == false) {
ESP_LOGD(TAG, "MH-Z19B detected");
this->model_b = true;
}

if (this->model_b && this->abc_disabled == false) {
uint8_t abc_ack[MHZ19_RESPONSE_LENGTH];
/*
* MH-Z19B allows to enable/disable 'automatic baseline calibration' (datasheet MH-Z19B v1.2),
* disable it to prevent sensor baseline drift in not well ventilated area
*/
ESP_LOGI(TAG, "Disabling ABC on boot");
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if (!this->mhz19_write_command_(MHZ19_COMMAND_ABC_DISABLE, abc_ack)) {
ESP_LOGW(TAG, "Failed to read ABC disable ack!");
return;
}
this->abc_disabled = true;
/*
* TODO: implement an option to recalibrate sensor, to allow for occasional
* manual recalibration
*/
}
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This whole block sounds a bit more like it should go in the setup() function. We should probably move it there.

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I've tried it first but then node hangs for good (had to restart mcu several times before I was able to flash it again) on boot. With UART0 occupied by sensor without hardware to read log from UART1 output, I don't have means to debug it.

I'd still like to move it to setup, but don't know how to fix boot issue.


uint8_t checksum = mhz19_checksum(response);
if (response[8] != checksum) {
ESP_LOGW(TAG, "MHZ19 Checksum doesn't match: 0x%02X!=0x%02X", response[8], checksum);
Expand All @@ -58,6 +100,19 @@ void MHZ19Component::update() {

bool MHZ19Component::mhz19_write_command_(const uint8_t *command, uint8_t *response) {
this->flush();

/*
* UART0 in NodeMCU v2, sometimes on boot has junk in RX buffer,
* check for it and drain all of it before sending commands to sensor
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Uhm the flush command should flush the RX buffer (naming is bad, but copied from arduino core). If it does not do so that would be a bug.

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That's make on it as well,
but got arduino/esp only a couple days ago so I'm not sure where to look for respective code
and this workaround fixed non working sensor for me.

If it's within this git repo and you can point out to related code, I'll give it a try.

*/
if (this->cleanup_rx_buffer) {
for (int i = 0; this->available(); i++) {
uint8_t junk;
this->read_byte(&junk);
ESP_LOGD(TAG, "junk in RX[%d]: %0x", i, junk);
}
}

this->write_array(command, MHZ19_REQUEST_LENGTH);
this->write_byte(mhz19_checksum(command));

Expand All @@ -74,7 +129,7 @@ MHZ19TemperatureSensor *MHZ19Component::make_temperature_sensor(const std::strin
MHZ19CO2Sensor *MHZ19Component::get_co2_sensor() const { return this->co2_sensor_; }
float MHZ19Component::get_setup_priority() const { return setup_priority::HARDWARE_LATE; }
void MHZ19Component::dump_config() {
ESP_LOGCONFIG(TAG, "MH-Z19:");
ESP_LOGCONFIG(TAG, "MH-Z19%s%s", this->model_b ? "B:" : "", this->abc_disabled ? " (auto calibration: disabled)": " (auto calibration: enabled)");
LOG_SENSOR(" ", "CO2", this->co2_sensor_);
LOG_SENSOR(" ", "Temperature", this->temperature_sensor_);
}
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3 changes: 3 additions & 0 deletions src/esphome/sensor/mhz19_component.h
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,9 @@ class MHZ19Component : public PollingComponent, public UARTDevice {

MHZ19TemperatureSensor *temperature_sensor_{nullptr};
MHZ19CO2Sensor *co2_sensor_;
bool model_b;
bool abc_disabled;
int cleanup_rx_buffer;
};

} // namespace sensor
Expand Down