STM32F103C8T6 Ultra-Low Power Modes – Deep Sleep & Standby

Complete guide to ultra-low power operation for STM32F103C8T6 (Blue Pill) – Stop Mode (50-500µA) and Standby Mode (2µA).

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Overview

The STM32F103C8T6 (Blue Pill) is a powerful ARM Cortex-M3 microcontroller, but it consumes 10-20mA in active mode – too high for battery-powered projects. Fortunately, the STM32 offers several low-power modes:

• Sleep Mode – CPU stops, peripherals continue.
• Stop Mode (Deep Sleep) – Almost everything halts, RAM retained, current ~50-500µA.
• Standby Mode – Ultra-low power (~2µA), RAM lost, reset on wake.

This page documents how to achieve ultra-low power consumption for the Blue Pill, including hardware optimisations, software configurations, and wake-up strategies.

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Architecture

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Power Mode Comparison

Mode	CPU	Peripherals	RAM	RTC	Wake Sources	Current
Active	Running	On	Retained	Optional	–	10-20mA
Sleep	Off	On	Retained	Optional	Any interrupt	2-5mA
Stop (Deep Sleep)	Off	Off (except RTC)	Retained	Optional	External interrupt, RTC	50-500µA
Standby	Off	Off	Lost	Optional	PA0 (WKUP), RTC alarm	~2µA

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Hardware Optimizations

1. Turn Off PC13 LED

The Blue Pill has a built-in LED on PC13. It draws current even in sleep modes if left on.

pinMode(PC13, OUTPUT);
digitalWrite(PC13, HIGH);  // Turn off LED (active LOW)

2. Bypass the AMS1117 Voltage Regulator

The onboard AMS1117-3.3V regulator consumes ~5-10mA continuously. Power the board via 3.3V directly to VCC to bypass it.

[Blue Pill]
  ┌─────────────┐
  │  VCC (3.3V) │ ← Power directly with 3.3V (bypass regulator)
  │  GND        │
  └─────────────┘

3. Disconnect USB-to-Serial Chip

If powered via USB, the CH340/CP2102 consumes ~2-10mA. For low-power operation, power externally and disconnect USB.

4. Disable Internal Pull-ups

Unused I/O pins with internal pull-ups may draw current. Configure them as analog inputs before sleep:

// Disable pull-ups on unused pins
pinMode(PB7, INPUT_ANALOG);  // Example
pinMode(PB6, INPUT_ANALOG);

5. Cut Power to External Sensors

Use a MOSFET to disconnect power to external peripherals (sensors, displays, etc.) before entering sleep.

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Stop Mode (Deep Sleep) – RAM Retained

Stop Mode is ideal when you need to retain RAM and resume quickly.

Example: Stop Mode with RTC Wake-Up (5 seconds)

#include <STM32LowPower.h>

#define LED PC13

void setup() {
    Serial.begin(9600);
    delay(1000);

    // Turn off LED
    pinMode(LED, OUTPUT);
    digitalWrite(LED, HIGH);

    Serial.println("Going to Deep Sleep...");
    delay(1000);

    LowPower.begin();
    LowPower.deepSleep(5000); // Sleep for 5 seconds
}

void loop() {
    Serial.println("Woke up from Deep Sleep!");
    digitalWrite(LED, LOW);
    delay(2000);
    digitalWrite(LED, HIGH);
    delay(500);
}

Power Consumption: ~50-500µA (depending on peripherals and clock).

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Standby Mode – Ultra Low Power (~2µA)

Standby Mode is the lowest power mode, consuming only ~2µA. However:

• RAM is lost – variables are reset.
• MCU resets on wake – execution starts from setup().
• Only PA0 (WKUP) and RTC alarm can wake the MCU.

Example 1: Standby Mode with PA0 Button Wake-Up

#include <STM32LowPower.h>

#define WAKEUP_PIN PA0  // Connect button from PA0 to GND

void setup() {
    Serial.begin(9600);
    delay(1000);

    pinMode(WAKEUP_PIN, INPUT_PULLUP);

    Serial.println("Entering Standby Mode in 3 seconds...");
    delay(3000);

    LowPower.begin();
    LowPower.enableWakeupFrom(WAKEUP_PIN, FALLING);  // Wake on button press
    LowPower.standby();  // Enter Standby (MCU resets on wake)
}

void loop() {
    Serial.println("Woke up from Standby!");
    delay(2000);
}

Wiring: Connect a button between PA0 and GND. Internal pull-up is enabled.

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Example 2: Standby Mode with RTC Alarm Wake-Up

#include <STM32LowPower.h>

#define WAKEUP_PIN PA0

void setup() {
    Serial.begin(9600);
    delay(1000);

    pinMode(WAKEUP_PIN, INPUT_PULLUP);

    Serial.println("Entering Standby Mode in 3 seconds...");
    delay(3000);

    LowPower.begin();
    
    // Enable both RTC alarm and external wake-up
    LowPower.enableWakeupFrom(RTC_ALARM);
    LowPower.enableWakeupFrom(WAKEUP_PIN, FALLING);

    // Standby for 10 seconds OR until button press
    LowPower.standby(10000);
}

void loop() {
    Serial.println("Woke up from Standby!");
    delay(2000);
}

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Complete Deep Sleep with RTC & External Interrupt

If you need RAM retention and flexible wake sources, use Stop Mode with both RTC and external interrupts:

#include <STM32LowPower.h>

#define WAKEUP_PIN PA0
#define LED PC13

void setup() {
    Serial.begin(9600);
    delay(1000);

    pinMode(LED, OUTPUT);
    digitalWrite(LED, HIGH);

    pinMode(WAKEUP_PIN, INPUT_PULLUP);
    attachInterrupt(WAKEUP_PIN, wakeUp, FALLING);

    Serial.println("Going to Deep Sleep...");
    delay(2000);

    LowPower.begin();
    LowPower.deepSleep(5000);  // Sleep 5s or until interrupt
}

void loop() {
    Serial.println("Woke up from Deep Sleep!");
    digitalWrite(LED, LOW);
    delay(2000);
    digitalWrite(LED, HIGH);
    delay(500);
}

void wakeUp() {
    // Empty ISR – just wakes the MCU
}

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Power Consumption Results

Condition	Current
Normal Running (LED ON, USB connected, AMS1117)	10-20mA
Deep Sleep (LED OFF, USB disconnected)	50-500µA
Optimized Standby (LED OFF, bypass regulator, no USB)	~2µA

Battery Life Estimate (1000mAh LiPo)

Mode	Current	Estimated Life
Active	15mA	67 hours
Deep Sleep	100µA	10,000 hours (~1.1 years)
Standby	2µA	500,000 hours (~57 years)

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Key Achievements

• ✅ Stop Mode – 50-500µA with RAM retention.
• ✅ Standby Mode – 2µA ultra-low power.
• ✅ Multiple wake sources – PA0 button, RTC alarm, external interrupts.
• ✅ Hardware optimizations – LED off, regulator bypass, USB disconnect.
• ✅ Production-ready – Code tested on Blue Pill with STM32Duino core.

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Technology Stack

Category	Technology
MCU	STM32F103C8T6 (Blue Pill)
Core	STM32Duino (Arduino IDE)
Library	STM32LowPower
Wake Sources	PA0 (WKUP), RTC Alarm, External Interrupts
Power Supply	3.3V (direct to VCC)

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Related Projects

• Embedded Systems Engineering – Main embedded systems page.
• Arduino Pro Mini Ultra-Low Power – Similar power optimization.
• Arduino Server-Side Compiler – STM32 support included.

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This STM32 low-power guide is part of my broader Embedded Systems Engineering practice. For a detailed technical walkthrough or custom battery-powered design, feel free to reach out.