Feed the watchdog only after critical health checks pass. The implementation must operate inside the electrical, timing and memory limits of the exact STM32 F1 device.
System design
Circuit & Wiring Studio
Exact target required
Drag components. In Connect mode, select one pin and then another pin.
// STM32 F1 — complete watchdog starter program
// Map BOARD_LED, BOARD_INPUT, ADC and serial helpers to the exact board support package.
#include "main.h"
#include <stdint.h>
#include <stdbool.h>
static uint32_t deadline_ms;static uint32_t faults;
static void safe_outputs(void){board_gpio_write(BOARD_LED,false);}
static void project_step(void){uint16_t sample=board_adc_read(0);bool input=board_gpio_read(BOARD_INPUT);bool output=(sample>2048u)||input;board_gpio_write(BOARD_LED,output);board_serial_printf("TYPE=watchdog ADC=%u IN=%u FAULTS=%lun",sample,input,(unsigned long)faults);}
int main(void){board_init();safe_outputs();board_serial_init(115200);board_serial_write("TCS STM32 F1 PROJECT READYn");deadline_ms=board_millis();for(;;){uint32_t now=board_millis();if((int32_t)(now-deadline_ms)>=0){deadline_ms+=100u;project_step();}board_watchdog_service_if_healthy();}}
Testing and observations
Inspect wiring with power disconnected.
Power from a current-limited supply.
Build with the exact target and warning level enabled.
Flash the program and capture startup output.
Measure supply and relevant I/O signals.
Inject one safe input or communication fault.
Repeat the functional test for at least 20 cycles.
Record code version, board revision and results.
Test
Expected
Instrument
Acceptance criteria
Supply rail
Within target-board tolerance
Idle current
Below approved project limit
Functional output
Matches the stated objective
Fault response
Safe and recoverable
Repeated test
20 of 20 cycles pass
Viva questions
Why was this pin selected?
Explain pin capability, boot function and voltage limit.
What fails if timing blocks?
Other work and fault response become delayed.
How was current limited?
Use a resistor, driver and protected supply as required.
What evidence proves operation?
Code version, measurements, serial output and repeated tests.
Prototype safety
Verify voltage, polarity, GPIO limits and isolation before power-up. Use current limiting and disconnect power before wiring changes.
Guided practical
Complete learning and build guide
Advanced6–10 hoursSecure OTA and production firmware
Objective
Feed the watchdog only after critical health checks pass.
Required knowledge
STM32 F1 pin functions and voltage limits
Embedded C/C++ fundamentals
Safe breadboard wiring
Serial debugging and measurement
Power and current calculation
Calculate total current from the board, sensor/module and output load. GPIO supplies only logic-level current; motors, relays, buzzers and high-current LEDs require a correctly rated driver and protected external rail. Start with current limiting and verify actual idle and peak current.
Libraries and build procedure
Libraries: STM32 HAL or LL generated for the exact MCU, No external paid API
Create a project for STM32 F1 using STM32CubeIDE.
Select the exact MCU/board and clock configuration.
Paste the complete program and change only the documented pin constants.
Install only the libraries listed for this project.
Build with warnings enabled and resolve every error.
Connect the board with outputs disconnected and upload/program it.
Confirm startup diagnostics, then connect the protected load.
Record the final binary size and test evidence.
Complete source code
// STM32 F1 — complete watchdog starter program
// Map BOARD_LED, BOARD_INPUT, ADC and serial helpers to the exact board support package.
#include "main.h"
#include <stdint.h>
#include <stdbool.h>
static uint32_t deadline_ms;static uint32_t faults;
static void safe_outputs(void){board_gpio_write(BOARD_LED,false);}
static void project_step(void){uint16_t sample=board_adc_read(0);bool input=board_gpio_read(BOARD_INPUT);bool output=(sample>2048u)||input;board_gpio_write(BOARD_LED,output);board_serial_printf("TYPE=watchdog ADC=%u IN=%u FAULTS=%lun",sample,input,(unsigned long)faults);}
int main(void){board_init();safe_outputs();board_serial_init(115200);board_serial_write("TCS STM32 F1 PROJECT READYn");deadline_ms=board_millis();for(;;){uint32_t now=board_millis();if((int32_t)(now-deadline_ms)>=0){deadline_ms+=100u;project_step();}board_watchdog_service_if_healthy();}}
Section
Explanation
Configuration
Selects the exact target pins, baud rate and safe defaults.
Initialisation
Configures peripherals and reports startup state.
Non-blocking loop
Schedules input, processing and output without long delays.
Fault handling
Detects invalid data or timeout and selects a safe output.
Diagnostics
Prints measurements and state for repeatable testing.
