10 KiB
RC CAR powered by ESP32-C3 Breadboard Adapter (controlled via ESP-NOW)
Designated Pins & GPIOs
The table below lists GPIOs/Pins programmed to delivery specific operating functions.
| GPIO | Pin | Assigned Functionality | Notes |
|---|---|---|---|
| 0 | 16 | Joystick x-axis | ADC1_CH0 |
| 1 | 15 | Joysticj y-axis | ADC1_CH1 |
| 8 | 5 | Joystick push button | |
| 6 | 4 | GPIO controlling clockwise rotation PWM of left motors | LEDC_CHANNEL_1 |
| 5 | 3 | GPIO controlling clockwise rotation PWM of right motors | LEDC_CHANNEL_0 |
| 4 | 2 | GPIO controlling counter clockwise rotation PWM of left motors | LEDC_CHANNEL_2 |
| 7 | 6 | GPIO controlling counter clockwise rotation PWM of right motors | LEDC_CHANNEL_3 |
Schematic
How Does It Work?
Hardware
Model Car Firmware
Controlling DC Motors
The Model Car uses four DC motors attached to mecanum wheels. The rotation magntutude of each DC motors is controlled by PWM. Each of corresponding PWM value is stored in a struct for later processing. The PWM value can take within a range from 0 to 8091.
DC motors PWM values are organized in a struct as follows:
struct motors_rpm {
int motor1_rpm_pcm;
int motor2_rpm_pcm;
int motor3_rpm_pcm;
int motor4_rpm_pcm;
};
Calculating Supported Range of PWM Values
The DC motors require digital PWM signals which, in turn, depend on analog signals supplied by the joystick stick. Consequently, analog values need to be interpreted into digital PWM signals. ESP32-C3 is capable of sampling voltage (analog signal) for the purpose of forming PWM signal.
As joystick x- and y- coordinates change, so do voltages on corresponding joystick analog outputs. Based on the hardware implementation, the voltage on x- and y- analog outputs can change witin a range from 0V to 3.3V . When ESP32-C3 takes sample of voltages on these outputs, ESP32-C ADC produces values witin a range from 0 to 2048. When joystick is in neutral position, the x- and y- values are (1024, 1024).
Once analog signals are measured, their magnitudes are converted into PWM values; in addition, PWM values cannot be nagative. When joystick is in neutral position, the PWM values for all four motors is 0. However, when joystick is moved Front, Back, Left or Right, the PWM values for corresponding motor(s) is(are) updated, and can take value up to 8091.
The ESP32-C3 is equipped with 14-bit counters (hence the maximum resolution of the PWM signal is 14 bits) that supply PWM timers with the reference clock. The counter counts up to 2^Resolution - 1, overflows and begins counting from 0 again.
The frequency of a PWM generator output signal is depedent on the frequency of the timer's clock source, the clock divisor, and the duty resolution (counter width).
The table below lists the commonly-used frequencies and their corresponding resolutions.
| LEDC_CLKx | PWM Frequency | Highest Resolution | Lowest Resolution |
|---|---|---|---|
| APB_CLK (80 MHZ) | 1kHz | 14 (16,384) | 7 (128) |
| APB_CLK (80 MHz) | 5kHz | 13 (8,192) | 4 (16) |
| APB_CLK (80 MHz) | 10 kHz | 12 (4,096) | 3 (8) |
| XTAL_CLK (40 MHz) | 1 kHz | 14 (16,384) | 6 (64) |
| XTAL_CLK (40 MHz) | 4 kHz | 13 (8,192) | 4 (16) |
| RC_FAST_CLK (17.5 MHz) | 1 kHz | 14 (16,384) | 5 (32) |
| RC_FAST_CLK (17.5 kHz} | 1.75 kHz | 13 (8,192) | 4 (16) |
ESP32-C3 Technical Reference Manual
Receiver & Controller (ESP-NOW) Firmware
ESP-NOW is used to communicate data between Controller and Receiver.
RC Controller
RC Controller uses the two ADC on ESP32-C3 to sample voltage levels on joystick x- and y- axis potentionometers. Then, these values are stored in a struct.
ESP32-C3 ADC supports 12-bit resolution, with the conversion voltage ranging from 0 mV to 1100 mV (by design). The input signals can be attenuated to 0dB, 2.5dB, 5dB or 12dB.
| Signal | Channel | ADC Selection |
|---|---|---|
| GPIO0 | 0 | SAR ADC1 |
| GPIO1 | 1 | SAR ADC1 |
| GPIO2 | 2 | SAR ADC1 |
| GPIO3 | 3 | SAR ADC1 |
| GPIO4 | 4 | SAR ADC1 |
| GPIO5 | 0 | SAR ADC2 |
| Attenuation | Measurable input voltage range |
|---|---|
| ADC_ATTEN_DB_0 | 100 mV ~ 950 mV |
| ADC_ATTEN_DB_2_5 | 100 mV ~ 1250 mV |
| ADC_ATTEN_DB_6 | 150 mV ~ 1750 mV |
| ADC_ATTEN_DB_11 | 150 mV ~ 2450 mV |
Analog to Digital Converter (ACD)
The potentionometers values are organized in a struct as follows:
// Struct holding sensors values
typedef struct {
uint16_t crc; // CRC16 value of ESPNOW data
uint8_t x_axis; // Joystick x-position
uint8_t y_axis; // Joystick y-position
bool nav_bttn; // Joystick push button
} __attribute__((packed)) sensors_data_t;
The function sendData() is a core function that sends data to the received using ESP-NOW.
// Function to send data to the receiver
void sendData (void) {
sensors_data_t buffer; // Declare data struct
buffer.crc = 0;
buffer.x_axis = 240;
buffer.y_axis = 256;
buffer.nav_bttn = 0;
buffer.motor1_rpm_pwm = 10;
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.");
}
Since ESP-NOW uses wireless module, Wi-Fi needs to be initialized before configuring ESP-NOW.
/* WiFi is required to run ESPNOW */
static void wifi_init(void)
{
ESP_ERROR_CHECK(esp_netif_init());
ESP_ERROR_CHECK(esp_event_loop_create_default());
wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();
ESP_ERROR_CHECK( esp_wifi_init(&cfg) );
ESP_ERROR_CHECK( esp_wifi_set_storage(WIFI_STORAGE_RAM) ); // Keep configurations in RAM
ESP_ERROR_CHECK( esp_wifi_set_mode(WIFI_MODE_STA)); // Do not change WiFi device mode
ESP_ERROR_CHECK( esp_wifi_start());
ESP_ERROR_CHECK( esp_wifi_set_channel(CONFIG_ESPNOW_CHANNEL, WIFI_SECOND_CHAN_NONE)); // Both sender & receiver must be on the same channel
}
The main function contains lines of code that initialize wireless, ESP-NOW, specify configuration variables, and start recurring task.
#include "esp_wifi.h"
void app_main(void)
{
// Initialize NVS to store Wi-Fi configurations
esp_err_t ret = nvs_flash_init();
if (ret == ESP_ERR_NVS_NO_FREE_PAGES || ret == ESP_ERR_NVS_NEW_VERSION_FOUND) {
ESP_ERROR_CHECK( nvs_flash_erase() );
ret = nvs_flash_init();
}
ESP_ERROR_CHECK( ret );
// ESP-NOW
wifi_init(); // Initialize Wi-Fi
esp_now_init(); // Call ESP-NOW initialization function
esp_now_register_recv_cb(onDataReceived); // Define call back for the event when data is being received
esp_now_register_send_cb(onDataSent); // Define call back for the event when data is sent received
// Set ESP-NOW receiver peer configuration values
memcpy (peerInfo.peer_addr, receiver_mac, 6); // Copy receiver MAC address
peerInfo.channel = 1; // Define communication channel
peerInfo.encrypt = false; // Keep data unencrypted
esp_now_add_peer(&peerInfo); // Add peer to
xTaskCreate (rc_send_data_task, "RC", 2048, NULL, 15, NULL);
}
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 second to send data over ESP-NOW.
// 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 (1000 / portTICK_PERIOD_MS);
}
}
Variables
| Variable | Value | Description |
|---|---|---|
| crc | ||
| x_axis | ||
| y_axis | ||
| nav_btn | ||
| motor1_rpm_pwm | ||
| motor2_rpm_pwm | ||
| motor3_rpm_pwm | ||
| motor4_rpm_pwm | ||
| MTR_FREQUENCY | 5000 | Default PWM frequency, Hz. |