hc-sr04

Sensor datasheet

• Needs a 10uS pulse
• Reading at 30Hz

Tricks

• Useful stm32 timer formulas
• Remember to start the timer
• Using bypass clock at 8MHz coming from ST-Link board
• Using TIM4, and CH3 and CH4 (for testing) for trigger
• APBx clocks are at 96MHz
• Prescaler at 50-1
• Period at 64000-1
• This gives a timer frequency of 30Hz
• Pulse is set to 19200 giving a 10ms pulse on PD14
• Using TIM4, CH1, PD12 for input capture, set to rising and falling edges
• Using interrupts to calculate the period of the echo pulse and the related distance
• Output (distance) is printed to USB configured as a virtual serial device