Support BL0942 calibration (#7299)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

CODEOWNERS

@@ -61,7 +61,7 @@ esphome/components/bk72xx/* @kuba2k2
 esphome/components/bl0906/* @athom-tech @jesserockz @tarontop
 esphome/components/bl0939/* @ziceva
 esphome/components/bl0940/* @tobias-
-esphome/components/bl0942/* @dbuezas
+esphome/components/bl0942/* @dbuezas @dwmw2
 esphome/components/ble_client/* @buxtronix @clydebarrow
 esphome/components/bluetooth_proxy/* @jesserockz
 esphome/components/bme280_base/* @esphome/core

esphome/components/bl0942/__init__.py

@@ -1 +1 @@
-CODEOWNERS = ["@dbuezas"]
+CODEOWNERS = ["@dbuezas", "@dwmw2"]

esphome/components/bl0942/bl0942.cpp

@@ -122,6 +122,20 @@ void BL0942::update() {
 }
 
 void BL0942::setup() {
+  // If either current or voltage references are set explicitly by the user,
+  // calculate the power reference from it unless that is also explicitly set.
+  if ((this->current_reference_set_ || this->voltage_reference_set_) && !this->power_reference_set_) {
+    this->power_reference_ = (this->voltage_reference_ * this->current_reference_ * 3537.0 / 305978.0) / 73989.0;
+    this->power_reference_set_ = true;
+  }
+
+  // Similarly for energy reference, if the power reference was set by the user
+  // either implicitly or explicitly.
+  if (this->power_reference_set_ && !this->energy_reference_set_) {
+    this->energy_reference_ = this->power_reference_ * 3600000 / 419430.4;
+    this->energy_reference_set_ = true;
+  }
+
   this->write_reg_(BL0942_REG_USR_WRPROT, BL0942_REG_USR_WRPROT_MAGIC);
   this->write_reg_(BL0942_REG_SOFT_RESET, BL0942_REG_SOFT_RESET_MAGIC);
 
@@ -184,11 +198,15 @@ void BL0942::dump_config() {  // NOLINT(readability-function-cognitive-complexit
   ESP_LOGCONFIG(TAG, "BL0942:");
   ESP_LOGCONFIG(TAG, "  Address: %d", this->address_);
   ESP_LOGCONFIG(TAG, "  Nominal line frequency: %d Hz", this->line_freq_);
+  ESP_LOGCONFIG(TAG, "  Current reference: %f", this->current_reference_);
+  ESP_LOGCONFIG(TAG, "  Energy reference: %f", this->energy_reference_);
+  ESP_LOGCONFIG(TAG, "  Power reference: %f", this->power_reference_);
+  ESP_LOGCONFIG(TAG, "  Voltage reference: %f", this->voltage_reference_);
   LOG_SENSOR("", "Voltage", this->voltage_sensor_);
   LOG_SENSOR("", "Current", this->current_sensor_);
   LOG_SENSOR("", "Power", this->power_sensor_);
   LOG_SENSOR("", "Energy", this->energy_sensor_);
-  LOG_SENSOR("", "frequency", this->frequency_sensor_);
+  LOG_SENSOR("", "Frequency", this->frequency_sensor_);
 }
 
 }  // namespace bl0942

esphome/components/bl0942/bl0942.h

@@ -8,6 +8,57 @@
 namespace esphome {
 namespace bl0942 {
 
+// The BL0942 IC is "calibration-free", which means that it doesn't care
+// at all about calibration, and that's left to software. It measures a
+// voltage differential on its IP/IN pins which linearly proportional to
+// the current flow, and another on its VP pin which is proportional to
+// the line voltage. It never knows the actual calibration; the values
+// it reports are solely in terms of those inputs.
+//
+// The datasheet refers to the input voltages as I(A) and V(V), both
+// in millivolts. It measures them against a reference voltage Vref,
+// which is typically 1.218V (but that absolute value is meaningless
+// without the actual calibration anyway).
+//
+// The reported I_RMS value is 305978 I(A)/Vref, and the reported V_RMS
+// value is 73989 V(V)/Vref. So we can calibrate those by applying a
+// simple meter with a resistive load.
+//
+// The chip also measures the phase difference between voltage and
+// current, and uses it to calculate the power factor (cos φ). It
+// reports the WATT value of 3537 * I_RMS * V_RMS * cos φ).
+//
+// It also integrates total energy based on the WATT value. The time for
+// one CF_CNT pulse is 1638.4*256 / WATT.
+//
+// So... how do we calibrate that?
+//
+// Using a simple resistive load and an external meter, we can measure
+// the true voltage and current for a given V_RMS and I_RMS reading,
+// to calculate BL0942_UREF and BL0942_IREF. Those are in units of
+// "305978 counts per amp" or "73989 counts per volt" respectively.
+//
+// We can derive BL0942_PREF from those. Let's eliminate the weird
+// factors and express the calibration in plain counts per volt/amp:
+// UREF1 = UREF/73989, IREF1 = IREF/305978.
+//
+// Next... the true power in Watts is V * I * cos φ, so that's equal
+// to WATT/3537 * IREF1 * UREF1. Which means
+// BL0942_PREF = BL0942_UREF * BL0942_IREF * 3537 / 305978 / 73989.
+//
+// Finally the accumulated energy. The period of a CF_CNT count is
+// 1638.4*256 / WATT seconds, or 419230.4 / WATT seconds. Which means
+// the energy represented by a CN_CNT pulse is 419230.4 WATT-seconds.
+// Factoring in the calibration, that's 419230.4 / BL0942_PREF actual
+// Watt-seconds (or Joules, as the physicists like to call them).
+//
+// But we're not being physicists today; we we're being engineers, so
+// we want to convert to kWh instead. Which we do by dividing by 1000
+// and then by 3600, so the energy in kWh is
+// CF_CNT * 419230.4 / BL0942_PREF / 3600000
+//
+// Which makes BL0952_EREF = BL0942_PREF * 3600000 / 419430.4
+
 static const float BL0942_PREF = 596;              // taken from tasmota
 static const float BL0942_UREF = 15873.35944299;   // should be 73989/1.218
 static const float BL0942_IREF = 251213.46469622;  // 305978/1.218
@@ -42,6 +93,22 @@ class BL0942 : public PollingComponent, public uart::UARTDevice {
   void set_frequency_sensor(sensor::Sensor *frequency_sensor) { frequency_sensor_ = frequency_sensor; }
   void set_line_freq(LineFrequency freq) { this->line_freq_ = freq; }
   void set_address(uint8_t address) { this->address_ = address; }
+  void set_current_reference(float current_ref) {
+    this->current_reference_ = current_ref;
+    this->current_reference_set_ = true;
+  }
+  void set_energy_reference(float energy_ref) {
+    this->energy_reference_ = energy_ref;
+    this->energy_reference_set_ = true;
+  }
+  void set_power_reference(float power_ref) {
+    this->power_reference_ = power_ref;
+    this->power_reference_set_ = true;
+  }
+  void set_voltage_reference(float voltage_ref) {
+    this->voltage_reference_ = voltage_ref;
+    this->voltage_reference_set_ = true;
+  }
 
   void loop() override;
   void update() override;
@@ -59,12 +126,16 @@ class BL0942 : public PollingComponent, public uart::UARTDevice {
 
   // Divide by this to turn into Watt
   float power_reference_ = BL0942_PREF;
+  bool power_reference_set_ = false;
   // Divide by this to turn into Volt
   float voltage_reference_ = BL0942_UREF;
+  bool voltage_reference_set_ = false;
   // Divide by this to turn into Ampere
   float current_reference_ = BL0942_IREF;
+  bool current_reference_set_ = false;
   // Divide by this to turn into kWh
   float energy_reference_ = BL0942_EREF;
+  bool energy_reference_set_ = false;
   uint8_t address_ = 0;
   LineFrequency line_freq_ = LINE_FREQUENCY_50HZ;
   uint32_t rx_start_ = 0;

esphome/components/bl0942/sensor.py

@@ -24,6 +24,11 @@ from esphome.const import (
     UNIT_WATT,
 )
 
+CONF_CURRENT_REFERENCE = "current_reference"
+CONF_ENERGY_REFERENCE = "energy_reference"
+CONF_POWER_REFERENCE = "power_reference"
+CONF_VOLTAGE_REFERENCE = "voltage_reference"
+
 DEPENDENCIES = ["uart"]
 
 bl0942_ns = cg.esphome_ns.namespace("bl0942")
@@ -77,6 +82,10 @@ CONFIG_SCHEMA = (
                 ),
             ),
             cv.Optional(CONF_ADDRESS, default=0): cv.int_range(min=0, max=3),
+            cv.Optional(CONF_CURRENT_REFERENCE): cv.float_,
+            cv.Optional(CONF_ENERGY_REFERENCE): cv.float_,
+            cv.Optional(CONF_POWER_REFERENCE): cv.float_,
+            cv.Optional(CONF_VOLTAGE_REFERENCE): cv.float_,
         }
     )
     .extend(cv.polling_component_schema("60s"))
@@ -106,3 +115,11 @@ async def to_code(config):
         cg.add(var.set_frequency_sensor(sens))
     cg.add(var.set_line_freq(config[CONF_LINE_FREQUENCY]))
     cg.add(var.set_address(config[CONF_ADDRESS]))
+    if (current_reference := config.get(CONF_CURRENT_REFERENCE, None)) is not None:
+        cg.add(var.set_current_reference(current_reference))
+    if (voltage_reference := config.get(CONF_VOLTAGE_REFERENCE, None)) is not None:
+        cg.add(var.set_voltage_reference(voltage_reference))
+    if (power_reference := config.get(CONF_POWER_REFERENCE, None)) is not None:
+        cg.add(var.set_power_reference(power_reference))
+    if (energy_reference := config.get(CONF_ENERGY_REFERENCE, None)) is not None:
+        cg.add(var.set_energy_reference(energy_reference))

tests/components/bl0942/test.bk72xx-ard.yaml

@@ -20,3 +20,7 @@ sensor:
       name: BL0942 Energy
     frequency:
       name: BL0942 Frequency
+    voltage_reference: 15968
+    current_reference: 124180
+    power_reference: 309.1
+    energy_reference: 2653

tests/components/bl0942/test.rp2040-ard.yaml

@@ -18,3 +18,5 @@ sensor:
       name: BL0942 Energy
     frequency:
       name: BL0942 Frequency
+    voltage_reference: 15968
+    current_reference: 124180