ESP32 Battery-Powered IoT Sensor Node

Modified: Mar. 5, 2026

Published: Mar. 5, 2026

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This lesson shifts from development boards to a purpose-built IoT sensor node. You will design a battery-powered board around the ESP32-C3-MINI-1, a compact RISC-V module with WiFi and BLE. The power system uses a TP4056 charging IC with solar panel input and lithium battery protection, feeding a low-quiescent-current LDO. Every design decision targets minimal sleep current so the board can run for months on a small battery. #KiCad #ESP32 #IoT

What We Are Building

Board specifications:

Bill of Materials

Power System Design

Battery Charging: TP4056

The TP4056 is a complete constant-current, constant-voltage linear charger for single-cell lithium batteries. It charges to 4.2V and automatically terminates when the charge current drops below a threshold (typically 1/10 of the programmed current).

Key connections:

• PROG pin: A resistor from PROG to GND sets the charge current. For 500 mA charging, use a 2 kΩ resistor. For solar charging with a small panel (100 mA), you might use a 10 kΩ resistor instead.
• VIN: Connect to the USB-C VBUS or solar panel output through the diode-OR network.
• BAT: Connect to the battery through the DW01A protection circuit.
• CHRG and STDBY: Open-drain outputs that drive the charging and standby indicator LEDs.

Charge current reference:

Solar and USB Input: Diode-OR

The circuit is straightforward:

• USB VBUS connects through D2 (SS14) to TP4056 VIN.
• Solar panel output connects through D1 (SS14) to TP4056 VIN.
• A 10 µF capacitor on VIN smooths the input.

When both sources are present, USB typically wins because the solar panel open-circuit voltage is usually around 5 to 6V and drops under load, while USB provides a stable 5V.

Battery Protection: DW01A + 8205A

The DW01A connects between B+ and B- of the battery. Its OD and OC pins drive the gates of the two MOSFETs in the 8205A. The 8205A sits between the battery negative terminal and system ground. When a fault is detected, the appropriate MOSFET turns off, disconnecting the battery.

Voltage Regulation: ME6211 LDO

The ME6211C33M5G provides a stable 3.3V output from the battery voltage (3.0V to 4.2V). Its key advantage for battery applications is the very low quiescent current, approximately 40 µA. This is the current the regulator itself consumes even when the load draws nothing.

• Input: Battery voltage (3.0V to 4.2V from the protected output)
• Output: 3.3V, up to 500 mA
• Dropout voltage: ~100 mV at light loads
• Input capacitor: 10 µF ceramic
• Output capacitors: 10 µF ceramic + 100 nF ceramic

Power Budget Calculation

Battery life estimate with a 500 mAh cell:

• Sleep current: ~51 µA
• Wake current: ~80 mA for WiFi TX, ~5 mA for sensor read
• Wake duration: ~5 seconds every 10 minutes (0.83% duty cycle)
• Average current: 51 µA + (80 mA x 0.0083) ≈ 51 µA + 664 µA ≈ 715 µA
• Battery life: 500 mAh / 0.715 mA ≈ 699 hours ≈ 29 days with WiFi

For BLE-only transmission (peak ~15 mA, wake ~2 seconds):

• Average current: 51 µA + (15 mA x 0.0033) ≈ 51 µA + 50 µA ≈ 101 µA
• Battery life: 500 mAh / 0.101 mA ≈ 4950 hours ≈ 206 days

With a small solar panel providing even modest charging on sunny days, the system can run indefinitely.

Deep Sleep Considerations for PCB Design

Resistor Values Matter

Every pull-up or pull-down resistor that connects a voltage rail to ground (through a GPIO or other node) creates a constant current leak. For a 3.3V rail:

Rules for battery-powered designs:

• Use 100 kΩ or higher for pull-ups/pull-downs where possible
• I2C pull-ups: use 10 kΩ instead of the common 4.7 kΩ. At 100 kHz I2C clock speed, 10 kΩ works reliably for short bus lengths (under 10 cm on a PCB)
• The EN pin pull-up on the ESP32-C3 can be 100 kΩ with a 1 µF capacitor for slow rise time

LED Power Waste

A typical indicator LED draws 5 to 20 mA. If a power LED stays on during deep sleep, it dominates the entire current budget. Solutions:

• Remove the power LED entirely (simplest approach for deployed sensor nodes)
• Add a solder jumper in series with the LED, so you can cut the trace after debugging
• Gate the LED with a MOSFET controlled by a GPIO (only illuminate when the processor is awake)

In this design, the TP4056 CHRG and STDBY LEDs only illuminate during charging, so they do not affect sleep current when running on battery alone.

Switchable Sensor Power

The circuit uses a SI2301 P-MOSFET:

• Source: 3.3V rail
• Drain: Sensor VCC (BME280 VDD)
• Gate: GPIO pin through a 100 kΩ pull-up to 3.3V

When the GPIO drives LOW, the MOSFET turns on and powers the sensor. When the GPIO is HIGH (or floating during deep sleep with the pull-up), the MOSFET turns off and the sensor draws zero current.

USB-UART Bridge Current

Many ESP32 development boards include a CP2102 or CH340 USB-to-UART bridge chip. These draw 5 to 15 mA even when idle, which destroys battery life. The ESP32-C3 has native USB support built into the chip, eliminating the need for an external bridge. This saves board space, BOM cost, and significant sleep current.

Schematic Capture

USB-C Connector

1. Place the USB-C connector (6-pin simplified)

   For a power and programming connection, you only need VBUS, GND, D+, D-, CC1, and CC2. Place two 5.1 kΩ resistors from CC1 and CC2 to GND. These tell the USB host that this is a device requesting default USB power (5V, up to 500 mA).

   Connect VBUS through Schottky diode D2 to the TP4056 VIN net.

2. Connect the USB data lines

   The ESP32-C3 native USB pins are GPIO18 (D-) and GPIO19 (D+). Route these directly from the USB-C connector to the module pins. No external components are needed; the ESP32-C3 handles USB internally.

TP4056 Charging Circuit

1. Place the TP4056 IC

   Connect VIN to the diode-OR output from USB and solar. Place a 10 µF input capacitor close to the VIN pin.

2. Set the charge current

   Place a 2 kΩ resistor from the PROG pin to GND. This programs a 500 mA charge current. If using a small solar panel as the primary source, consider 10 kΩ (130 mA) to match the panel’s output capability.

3. Add status LEDs

   Connect CHRG to LED1 (red) through a 1 kΩ resistor to VIN. Connect STDBY to LED2 (green) through a 1 kΩ resistor to VIN. Both pins are open-drain, so they sink current through the LEDs.

4. Connect BAT to the protection circuit

   The TP4056 BAT pin connects to the positive terminal of the DW01A protection circuit (B+ net).

Solar Panel Input

1. Place the solar panel connector (J3)

   Use a JST-PH 2-pin connector. Connect the positive pin through Schottky diode D1 to the TP4056 VIN net (same net as the USB diode output).

2. Add reverse polarity protection

   The Schottky diode D1 also prevents current from flowing back into the solar panel when USB is connected or the battery voltage exceeds the panel voltage.

Battery Protection Circuit

1. Place the DW01A

   Connect VCC to B+ (battery positive). Connect VSS to the drain of the low-side MOSFET in the 8205A. The OD (overdischarge) and OC (overcharge/overcurrent) pins connect to the gates of the two MOSFETs in the 8205A.

2. Place the 8205A dual MOSFET

   The 8205A contains two N-channel MOSFETs in series. Connect the source of one MOSFET to the battery negative terminal (B-). Connect the drain of the other MOSFET to system ground (GND). The gates connect to the DW01A OD and OC pins.

3. Add the current sense resistor path

   Place a 100 kΩ resistor from the DW01A CS pin to the junction between the two MOSFETs. This is the current sense input for overcurrent detection.

Battery Connector

Place a JST-PH 2-pin connector (J2) for the battery. Connect the positive pin to B+ (feeding into the DW01A protection). Connect the negative pin to B- (battery ground, before the protection MOSFETs).

ME6211 LDO

1. Place the ME6211C33M5G

   Connect VIN to the protected battery output (the system side of the 8205A, which is the node between the TP4056 BAT pin and the load). Place a 10 µF input capacitor close to VIN.

2. Add output capacitors

   Place a 10 µF ceramic and a 100 nF ceramic on the 3.3V output, close to the VOUT pin. The ME6211 requires at least 1 µF output capacitance for stability.

3. Connect EN

   Tie the enable pin directly to VIN so the regulator is always on when battery voltage is present.

ESP32-C3-MINI-1 Module

1. Place the module

   The ESP32-C3-MINI-1 has castellated pads around its edges and a large ground pad underneath. Connect VCC (pin 2) to the 3.3V rail. Connect all GND pins and the exposed pad to GND.

2. Add decoupling

   Place a 10 µF bulk capacitor and a 100 nF capacitor close to the VCC pin.

3. EN (enable) circuit

   Connect a 100 kΩ pull-up resistor from EN to 3.3V. Add a 1 µF capacitor from EN to GND for a slow rise time, which ensures reliable startup. Connect the reset button (SW1) between EN and GND.

4. Boot button

   Connect SW2 between GPIO9 and GND. Holding GPIO9 low during reset puts the ESP32-C3 into download mode for flashing firmware over USB.

5. I2C pins for BME280

   Assign GPIO4 as SDA and GPIO5 as SCL. Place 10 kΩ pull-up resistors from each to the 3.3V rail.

6. Sensor power control

   Assign GPIO3 as the sensor power control pin. Connect it to the gate of the P-MOSFET (Q2) through a 100 Ω gate resistor for EMI damping.

BME280 Sensor

1. Place the BME280

   The BME280 comes in a tiny LGA-8 package (2.5 x 2.5 mm). Connect VDD to the switched 3.3V rail (drain of Q2). Connect GND to ground. Place a 100 nF decoupling capacitor close to VDD.

2. Set the I2C address

   Connect the SDO pin to GND for I2C address 0x76, or to VDD for address 0x77. GND is the more common choice.

3. Connect I2C

   Connect SDA to GPIO4 and SCL to GPIO5 on the ESP32-C3. The pull-up resistors are already on the main 3.3V rail, which means I2C communication works even when the sensor power MOSFET is off (the pull-ups hold the lines high).

4. CSB pin

   Connect CSB to VDD (the switched rail) to select I2C mode. If CSB is left floating, the BME280 may enter SPI mode.

Run ERC and Assign Footprints

1. Run Electrical Rules Check

   Fix any unconnected pins, missing power flags, or conflicting outputs. Add power flags on the battery input net and USB VBUS net if KiCad reports them as undriven.

2. Assign footprints

   Use the footprint assignment tool to map each symbol to its physical package. The ESP32-C3-MINI-1 footprint may need to be downloaded from Espressif’s KiCad library or the SnapEDA/Ultra Librarian services.

3. Generate the netlist

   Export the netlist and open the PCB editor.

PCB Layout

Board Setup

1. Set the board outline

   Draw a 45 x 30 mm rectangle on the Edge.Cuts layer. Add rounded corners with a 1 mm radius for a cleaner look and easier handling.

2. Configure design rules

   Set minimum trace width to 0.15 mm, minimum clearance to 0.15 mm. For power traces (VBAT, 3.3V, GND), use 0.4 mm or wider. USB data traces can use 0.25 mm.

3. Set up the ground pour

   Plan for copper fills on both front and back layers connected to GND. Do not pour them yet; wait until all traces are routed.

Component Placement

1. Place the ESP32-C3-MINI-1 module

   Position it along one short edge of the board with the antenna extending past the board edge or flush with it. The antenna end must have no copper on any layer within 2 mm of the antenna area.

2. Place the USB-C connector

   Position it on the opposite short edge from the antenna. This keeps the USB cable away from the antenna, reducing interference.

3. Place the TP4056 and protection circuit

   Group the TP4056, DW01A, 8205A, and their associated passives near the USB-C connector and battery connector. The TP4056 dissipates heat during charging (up to ~1.5W at 500 mA from 5V to a 3.7V battery), so place it with access to a copper pour for heat spreading.

4. Place the battery and solar connectors

   Position J2 (battery) and J3 (solar) along one long edge of the board. Through-hole JST connectors need clearance for the housing.

5. Place the ME6211 LDO

   Position it between the charging/protection section and the ESP32-C3. Keep input and output capacitors within 3 mm of the IC.

6. Place the BME280

   Position it away from the TP4056 and LDO to avoid heat from those components affecting temperature readings. The ideal location is near the board edge, far from heat sources. Consider adding a routed slot or thermal relief cutout in the PCB between the sensor and the power section.

7. Place buttons and LEDs

   Position the reset and boot buttons where they are accessible. Place the charging LEDs near the USB connector.

Antenna Keepout Zone

In KiCad, draw a keepout area on both copper layers covering the antenna region. Set the keepout to prohibit copper fills and tracks. The Espressif datasheet specifies the exact dimensions.

Thermal Management for TP4056

The TP4056 in SOP-8 package does not have an exposed thermal pad, so it relies on the PCB copper for heat dissipation. During charging at 500 mA from a 5V source into a 3.7V battery, the IC dissipates approximately:

P = (5V - 3.7V) x 0.5A = 0.65W

This is manageable, but the copper area around the thermal pad and GND pins should be as large as practical. Connect the GND pad to a wide copper pour on both layers with multiple vias.

Routing Guidelines

1. Route power traces first

   Start with VBAT, 3.3V, and GND. Use 0.4 mm or wider traces. Keep the path from the LDO output to the ESP32-C3 VCC short and direct.

2. Route USB data lines

   Keep D+ and D- as a parallel pair with consistent spacing. Match their lengths to within 0.5 mm. Avoid routing them near switching signals or the antenna.

3. Route I2C lines

   SDA and SCL to the BME280. These are low-speed signals, so routing is straightforward. Keep them reasonably short and away from the antenna area.

4. Fill copper zones

   Pour ground fills on both front and back layers. Add vias to stitch the ground planes together, especially near the ESP32 module ground pad and the TP4056 ground area.

5. Run DRC

   Check for clearance violations, unrouted nets, and minimum width errors. Fix any issues before generating Gerbers.

Manufacturing

Upload to JLCPCB or your preferred fabricator. For this 2-layer board, standard settings work well:

Order a stencil for the top layer if you plan to reflow solder the QFN and LGA components. The BME280 in LGA-8 and the 8205A in TSSOP-8 are much easier to solder with paste and hot air or a reflow oven than by hand.

Firmware: Deep Sleep Sensor Reading

Arduino Setup

Install the ESP32 board package in Arduino IDE (or PlatformIO). Select “ESP32C3 Dev Module” as the board. Install the Adafruit BME280 library and the Adafruit Unified Sensor library from the Library Manager.

Complete Sketch

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>

// Pin definitions
#define SDA_PIN 4
#define SCL_PIN 5
#define SENSOR_POWER_PIN 3

// Deep sleep duration: 10 minutes in microseconds
#define SLEEP_DURATION_US 600000000ULL

// BME280 I2C address (SDO to GND = 0x76)
#define BME280_ADDR 0x76

Adafruit_BME280 bme;

void setup() {
  // Initialize USB serial
  Serial.begin(115200);
  delay(100);

  // Power on the BME280 sensor
  pinMode(SENSOR_POWER_PIN, OUTPUT);
  digitalWrite(SENSOR_POWER_PIN, LOW); // P-MOSFET: LOW = ON

  // Wait for sensor power to stabilize
  delay(50);

  // Initialize I2C
  Wire.begin(SDA_PIN, SCL_PIN);

  // Initialize BME280
  if (!bme.begin(BME280_ADDR, &Wire)) {
    Serial.println("BME280 not found. Check wiring.");
    goToSleep();
    return;
  }

  // Set BME280 to forced mode for single reading
  bme.setSampling(
    Adafruit_BME280::MODE_FORCED,
    Adafruit_BME280::SAMPLING_X1,  // temperature
    Adafruit_BME280::SAMPLING_X1,  // pressure
    Adafruit_BME280::SAMPLING_X1,  // humidity
    Adafruit_BME280::FILTER_OFF,
    Adafruit_BME280::STANDBY_MS_0_5
  );

  // Take a forced measurement
  bme.takeForcedMeasurement();

  // Read sensor data
  float temperature = bme.readTemperature();
  float humidity = bme.readHumidity();
  float pressure = bme.readPressure() / 100.0F; // hPa

  // Print data
  Serial.println("=== IoT Sensor Reading ===");
  Serial.print("Temperature: ");
  Serial.print(temperature, 1);
  Serial.println(" C");
  Serial.print("Humidity: ");
  Serial.print(humidity, 1);
  Serial.println(" %");
  Serial.print("Pressure: ");
  Serial.print(pressure, 1);
  Serial.println(" hPa");
  Serial.println("==========================");
  Serial.flush();

  // Power off the sensor
  digitalWrite(SENSOR_POWER_PIN, HIGH); // P-MOSFET: HIGH = OFF

  // Go to deep sleep
  goToSleep();
}

void goToSleep() {
  Serial.println("Entering deep sleep for 10 minutes...");
  Serial.flush();

  // Configure deep sleep timer
  esp_sleep_enable_timer_wakeup(SLEEP_DURATION_US);

  // Enter deep sleep
  esp_deep_sleep_start();
}

void loop() {
  // This never executes. After deep sleep,
  // the ESP32-C3 resets and runs setup() again.
}

How It Works

The ESP32-C3 deep sleep mechanism resets the processor on wake. Execution always starts from setup(), not from where it left off. The RTC memory retains a small amount of data across sleep cycles if needed (for example, a boot counter or accumulated readings).

The firmware flow:

1. Wake from deep sleep (or initial power-on)
2. Drive GPIO3 LOW to turn on the sensor power MOSFET
3. Wait 50 ms for the sensor power rail to stabilize
4. Initialize I2C and the BME280
5. Take a forced measurement (single reading, lowest power)
6. Read temperature, humidity, and pressure
7. Print the data over USB serial
8. Drive GPIO3 HIGH to turn off the sensor
9. Enter deep sleep for 10 minutes

To add WiFi transmission, insert a WiFi connect and HTTP POST (or MQTT publish) between step 7 and step 8. WiFi adds approximately 3 to 5 seconds of wake time and 80 to 150 mA of current draw.

PlatformIO Alternative

If you prefer PlatformIO, create a project with the following platformio.ini:

[env:esp32c3]
platform = espressif32
board = esp32-c3-devkitm-1
framework = arduino
monitor_speed = 115200
lib_deps =
    adafruit/Adafruit BME280 Library@^2.2.2
    adafruit/Adafruit Unified Sensor@^1.1.9

The source code is identical. Place it in src/main.cpp.

What You Have Learned