SonarBoard

Firmware for STm32F303 Nucleo32 board to handle up to four HC-SR04 ultrasonic range sensors

Description

HC-SR04 module is a 2-wires driven distance sensor. It is triggered by a TTL 10 microsec pulse on "Trig" pin and the measured distance is proportional to the duration of the echo pulse received on the "Echo" pin.

• The Trig pulse is generated using a PWM timers programmed in "One Pulse mode".
• The Echo duration is measured using a timer in "Input Capture" coupling two channels: channel 1 triggers on rising edge on echo reception, channel 2 triggers on falling edge when the echo stops.

Sensor Configuration

The sensors are triggered coupled two by two to avoid echo interferences, only two triggers are generated to enable two sonars, 4 timers are required to measure the 4 echos.

Typical configuration:

      --- Sonar #0 ----------- Sonar #1 ---
      |                                   |
      |                                   |
      |                                   |
      --- Sonar #3 ----------- Sonar #2 ---

• The sensor #0 and the sensor #2 receive the same trigger
• The sensor #1 and the sensor #3 receive the same trigger

Pinout

Nucleo32

• PA6 - Trigger sensor #0 #2 [TMR16 CH1 PWM SINGLE SHOT]
• PA7 - Trigger sensor #1 #3 [TMR17 CH1 PWM SINGLE SHOT]
• PA8 - Echo sensor #0 [TMR1 CH1 INPUT CAPTURE DIRECT - CH2 INPUT CAPTURE INDIRECT]
• PA0 - Echo sensor #1 [TMR2 CH1 INPUT CAPTURE DIRECT - CH2 INPUT CAPTURE INDIRECT]
• PB4 - Echo sensor #2 [TMR3 CH1 INPUT CAPTURE DIRECT - CH2 INPUT CAPTURE INDIRECT]
• PA2 - Echo sensor #3 [TMR15 CH1 INPUT CAPTURE DIRECT - CH2 INPUT CAPTURE INDIRECT]
• PA9 - USART 1 TX
• PA10 - USART 1 RX
• PB3 - Board Green Led

NOTE #1: The Nucleo32 board is powered by an external 5V power supply, so SB1 must be opened.

NOTE #2: To enable the input pin for Sensor #3 echo on PA2 you need to open SB3 and SB2, disabling USART2 for Virtual COM Port - [For further information see Table 6 on document UM1956 "STM32 Nucleo-32 boards - User Manual" - http://www.st.com/st-web-ui/static/active/en/resource/technical/document/user_manual/DM00231744.pdf]

Serial communication

Baudrate 115200 8N1

Serial output

To emit range measures the board uses a binary protocol:

• Unsigned int 16 bit Sync word [0x5aa5]
• Unsigned int 32 bit number of bytes following [30]
• Unsigned int 32 bit ticks since system start
• float not_valid_val the float value used for not valid measured ranges
• float Sensor #0
• float Sensor #1
• float Sensor #2
• float Sensor #3
• Unsigned int 16 bit Number of sonar connected
• Unsigned int 16 bit Termination word [0x0d0a]

The data is mapped by the following C/C++ structure:

typedef struct _data_out
{
    uint16_t ctrl_frame_0;        // SYNC WORD [0x5aa5]
    uint16_t byte_count;          // number of bytes following [30]
    uint32_t ticks;               // ticks since system start
    float not_valid_val;          // value for not valid distances
    float distances[MAX_SONAR];   // distances in meters
    uint16_t sonar_active;        // Number of sonar connected
    uint16_t ctrl_frame_1;        // TERMINATION WORD [0x0d0a]
} DataOut;

[...]
DataOut data;
char buf[33];
memcpy( buf, &data, sizeof(DataOut) );
[...]

Serial input

No input allowed yet