HOW DOES IT WORK?

The BitByteRider RC car is powered by ESP32-C3 Breadboard & Power adapter developmemt board. The Schematic and KiCAd PCB board are available on GitHub: https://github.com/alexandrebobkov/ESP32-C3_Breadboard-Adapter

Reserved Pins & GPIOs

The following table summarizes GPIOs and pins reserved for operations purposes.

The GPIO numbers correspond to those on the ESP32-C3 WROOM microcontroller. The Pin number corresponds to the pin on the Breadboard and Power adapter development board.

x- and y- axis

The GPIO0 and GPIO1 assigned to measuring the voltage of x- and y- axis of the Joystick. Lastly, there is a group of GPIO pairs responsible for PWM for DC motors.

Direction and Speed

The pairs of DC motors on the left side are wired to the dedicated PWM channels. This means that ESP32-C3 Breadboard DevBoard can control rotation speed and direction of DC motors in pairs only (i.e. left and right side). Consequently, only four PWM channels are sufficient for controlling the direction of the RC car. Based on this constraint, the RC car can only move front, back, and turn/rotate left and right. Any other movements are not possible (i.e. diagonal or sideways).

A pair of PWM channels are required for defining rotation speed and direction of the DC motors on each side. In particular, GPIO6 and GPIO5 provide PWM to the left- and right- side DC motors to rotate in a clockwise direction. Similarly, GPIO4 and GPIO7 provide PWM to the left- and right- side DC motors to rotate in a counter-clockwise direction. Changing PWM on each channel determines the speed and direction of the RC car.

The following images illustrate various PWM duty cycles registered by oscilloscope (duty cycles 0%, 48% and 91%, resp.).

DC Motor PWM duty cycle 0%

DC Motor PWM duty cycle 47.6%

DC Motor PWM duty cycle 90.8%

GPIO	Pin	Function	Notes
0	16	Joystick x-axis	ADC1_CH0
1	15	Joystick y-axis	ADC1_CH1
8	5	Joystick push button
6	4	PWM for clockwise rotation of left-side motors	LEDC_CHANNEL_1
5	3	PWM for clockwise rotation of right-side motors	LEDC_CHANNEL_0
4	2	PWM for counter-clockwise rotation of right-side motors	LEDC_CHANNEL_2
7	6	PWM for counter-clockwise rotation of left-side motors	LEDC_CHANNEL_3

Fusion of Software with Hardware

The struct for storing motors PWM values.

struct motors_rpm {
    int motor1_rpm_pwm;
    int motor2_rpm_pwm;
    int motor3_rpm_pwm;
    int motor4_rpm_pwm;
};

The function for updating motors’ PWM values.

// Function to send data to the receiver
void sendData (void) {
    sensors_data_t buffer;              // Declare data struct

    buffer.crc = 0;
    buffer.x_axis = 0;
    buffer.y_axis = 0;
    buffer.nav_bttn = 0;
    buffer.motor1_rpm_pwm = 0;
    buffer.motor2_rpm_pwm = 0;
    buffer.motor3_rpm_pwm = 0;
    buffer.motor4_rpm_pwm = 0;

    // Display brief summary of data being sent.
    ESP_LOGI(TAG, "Joystick (x,y) position ( 0x%04X, 0x%04X )", (uint8_t)buffer.x_axis, (uint8_t)buffer.y_axis);
    ESP_LOGI(TAG, "pwm 1, pwm 2 [ 0x%04X, 0x%04X ]", (uint8_t)buffer.pwm, (uint8_t)buffer.pwm);
    ESP_LOGI(TAG, "pwm 3, pwm 4 [ 0x%04X, 0x%04X ]", (uint8_t)buffer.pwm, (uint8_t)buffer.pwm);

    // Call ESP-NOW function to send data (MAC address of receiver, pointer to the memory holding data & data length)
    uint8_t result = esp_now_send(receiver_mac, &buffer, sizeof(buffer));

    // If status is NOT OK, display error message and error code (in hexadecimal).
    if (result != 0) {
        ESP_LOGE("ESP-NOW", "Error sending data! Error code: 0x%04X", result);
        deletePeer();
    }
    else
        ESP_LOGW("ESP-NOW", "Data was sent.");
}

The onDataReceived() and onDataSent() are two call-bacl functions that get evoked on each corresponding event.

// Call-back for the event when data is being received
void onDataReceived (uint8_t *mac_addr, uint8_t *data, uint8_t data_len) {

    buf = (sensors_data_t*)data;                            // Allocate memory for buffer to store data being received
    ESP_LOGW(TAG, "Data was received");
    ESP_LOGI(TAG, "x-axis: 0x%04x", buf->x_axis);
    ESP_LOGI(TAG, "x-axis: 0x%04x", buf->y_axis);
    ESP_LOGI(TAG, "PWM 1: 0x%04x", buf->motor1_rpm_pwm);
}

// Call-back for the event when data is being sent
void onDataSent (uint8_t *mac_addr, esp_now_send_status_t status) {
    ESP_LOGW(TAG, "Packet send status: 0x%04X", status);
}

The rc_send_data_task() function runs every 0.1 second to transmit the data to the receiver.

// Continous, periodic task that sends data.
static void rc_send_data_task (void *arg) {

    while (true) {
        if (esp_now_is_peer_exist(receiver_mac))
            sendData();
        vTaskDelay (100 / portTICK_PERIOD_MS);
    }
}

Schematic