fix (firmware, schematic, layout): change vref for adc and resistors …

…to measure battery voltage

.vscode/settings.json

@@ -21,6 +21,7 @@
     "iterator": "cpp",
     "serstream": "cpp",
     "__locale": "cpp",
-    "unordered_set": "cpp"
+    "unordered_set": "cpp",
+    "complex": "cpp"
   }
 }

_code/measure-battery-level.md

@@ -1,37 +1,36 @@
 ---
 layout: code
 title: Measure battery voltage
-description: View the battery voltage through an access point
+description: Measure battery level using the ESP32-C3 ADC
 references:
   - name: Schematic of ESP32-C3-DevKitM-1
     url: https://dl.espressif.com/dl/schematics/SCH_ESP32-C3-DEVKITM-1_V1_20200915A.pdf
   - name: Pinouts
     url: https://docs.espressif.com/projects/esp-idf/en/latest/esp32c3/hw-reference/esp32c3/user-guide-devkitm-1.html#pin-layout
   - name: Arduino Pins
     url: https://github.com/espressif/arduino-esp32/blob/master/variants/esp32c3/pins_arduino.h
-  - name: Create an Access Point
-    url: https://raw.githubusercontent.com/espressif/arduino-esp32/990e3d5b431b63b4adc364b045a79afdad645a3f/libraries/WiFi/examples/WiFiAccessPoint/WiFiAccessPoint.ino
   - name: How to check the battery voltage
     url: https://wiki.seeedstudio.com/check_battery_voltage/
   - name: Power Management
     url: https://learn.adafruit.com/adafruit-feather-m4-express-atsamd51/power-management#measuring-battery-3010518
+  - name: ESP32-C3 ADC issue - reading 4095 at 2.8V
+    url: https://forum.arduino.cc/t/esp32-c3-adc-issue-reading-4095-at-2-8v/1127687
+  - name: Analog to Digital Converter (ADC)
+    url: https://docs.espressif.com/projects/esp-idf/zh_CN/v4.4.2/esp32c3/api-reference/peripherals/adc.html
+  - name: Voltage Divider Calculator
+    url: https://ohmslawcalculator.com/voltage-divider-calculator
+  - name: ESP32 ADC – Read Analog Input in Arduino IDE
+    url: https://deepbluembedded.com/esp32-adc-tutorial-read-analog-voltage-arduino/
 difficulty: medium
 features:
   - esp32c3
-  - access
-  - point
+  - adc
   - measure
   - battery
   - voltage
 images:
-  # prototype: demo-prototype.jpg
-  # console: demo-console.png
-  # schematic: schematic.png
+  prototype: demo-prototype.jpg
+  console: measure-battery-level-console.png
 ---
 
-1. Upload the firmware with `make`
-1. Remove the USB-C cable used for firmware upload
-1. Turn on the power switch
-1. Connect to access point `batt` with password `12345678`
-1. Browser to `http://192.168.4.1` on the browser
-1. View `hello world`
+This code measure the battery voltage using the ESP32-C3 ADC. The battery voltage is measured using a voltage divider circuit. The voltage divider circuit is used to scale down the battery voltage to a level that can be measured by the ESP32-C3 ADC. The ESP32-C3 ADC has a 12-bit resolution.

_code/measure-battery-level/Makefile

@@ -9,7 +9,7 @@ BUILD = build
 default: lint compile upload clean
 
 lint:
-	cpplint --extensions=ino --filter=-legal/copyright,-runtime/int,-readability/todo *.ino
+	cpplint --extensions=ino --filter=-legal/copyright,-runtime/int,-readability/todo,-whitespace/line_length *.ino
 
 compile: clean lint
 	arduino-cli compile --fqbn $(BOARD) --output-dir $(BUILD) ./

_code/measure-battery-level/measure-battery-level.ino

@@ -1,60 +1,61 @@
-// The code turns ON the MOSFET for 2 seconds
-// and then turns it OFF for 2 seconds.
-// The LED is also turned ON and OFF to indicate the state of the MOSFET.
-// The serial monitor is used to print the state of the MOSFET.
-
 #define LED 3
 #define BATTERY_ENABLE_PIN 6
 #define BATTERY_MEASURE_PIN 0
 
-const float R1 = 10000.0;  // 10kΩ
-const float R2 = 100000.0;  // 100kΩ
-const float Vref = 3.3;  // Reference voltage for ADC (3.3V for ESP32-C3)
+// TODO: Amend to 100kΩ resistors in the PCB for lower current consumption
+const float R1 = 33000.0;  // 33kΩ
+const float R2 = 33000.0;  // 33kΩ
 const int adcMax = 4095;  // 12-bit ADC resolution
 
+// https://forum.arduino.cc/t/esp32-c3-adc-issue-reading-4095-at-2-8v/1127687/7
+const float Vref = 2.84;  // Reference voltage for ADC (2.8=(V for ESP32-C3)
+
 void setup() {
   Serial.begin(115200);
   Serial.println();
 
   pinMode(LED, OUTPUT);
   pinMode(BATTERY_ENABLE_PIN, OUTPUT);
-  digitalWrite(BATTERY_ENABLE_PIN, HIGH);  // Turn OFF the MOSFET
+  digitalWrite(BATTERY_ENABLE_PIN, HIGH);
 }
 
 void loop() {
   digitalWrite(LED, HIGH);
-  Serial.println("MOSFET is ON");
-  digitalWrite(BATTERY_ENABLE_PIN, LOW);  // Turn ON the MOSFET
 
+  digitalWrite(BATTERY_ENABLE_PIN, LOW);
   delayMicroseconds(10);
   int sum = 0;
+
   for (int i = 0; i < 100; i++) {
     sum = sum + analogRead(BATTERY_MEASURE_PIN);
   }
-
   float adcValue = sum / 100.0;
   Serial.print("Raw ADC Value: ");
   Serial.println(adcValue);
 
   float voltageAtPin = (adcValue / adcMax) * Vref;
   Serial.print("Voltage at Pin: ");
-  Serial.println(voltageAtPin);
+  Serial.print(voltageAtPin);
+  Serial.println("V");
 
   float batteryVoltage = voltageAtPin * ((R1 + R2) / R2);
   Serial.print("Battery Voltage: ");
-  Serial.println(batteryVoltage);
-
+  Serial.print(batteryVoltage);
+  Serial.println("V");
 
-  float batteryLevel = (batteryVoltage - 3.0) / (4.2 - 3.0) * 100;
   // 3.0: Minimum voltage of the battery
   // 4.2: Maximum voltage of the battery
   // 100: Maximum battery level in percentage
+  float batteryLevel = (batteryVoltage - 3.0) / (4.2 - 3.0) * 100;
   Serial.print("Battery Level: ");
   Serial.print(batteryLevel);
+  Serial.println("%");
+
+  delay(2000);
 
-  digitalWrite(BATTERY_ENABLE_PIN, HIGH);  // Turn OFF the MOSFET
+  digitalWrite(BATTERY_ENABLE_PIN, HIGH);
   digitalWrite(LED, LOW);
-  Serial.println("MOSFET is OFF");
-  Serial.println("-------------------- ");
-  delay(4000);
+
+  Serial.println();
+  delay(2000);
 }