Harvest Rover

Figure 1 - Rover Image

The Harvest Rover is a small embedded system designed to participate in a competition known as The Harvest. During the competition, Rovers will participate by completing various tasks. These include:

RFID Sequence
Optical Signal Decoding
Environmental Remediation
Solar Array
Laser Turret
Magnetic Anomaly
Autonomous Line
Alien Frequency
Electrical Conductivity
IR Detection

This rover is specifically designed to complete 4 tasks:

RFID Sequence
Optical Signal Decoding
Solar Array
Alien Frequency

Hardware:

MPLAB Xpress Development Board (PIC16F18855)
Snap Programmer
PCU - (microbit) (Proprietary)
RCLS - dsPIC33CK128MP205 (Proprietary)
RFID Reader - RC522 RFID MODULE
Color Sensor - APDS-9960 - Light, Ambient Sensor Evaluation Board
Speaker - Passive Buzzer
Microphone - SPW2430 - MEMS Omnidirectional Microphones Audio Evaluation Board
Op-Amp - Standard (General Purpose) Amplifier 2 Circuit Rail-to-Rail 8-PDIP
Bright LED - C512A-WNN-CZ0B0151-ND
Driving MOSFET - 2N7000FS-ND
Saleae Logic Analyzer
Flysky transmitter and receiver

Software:

Setup

Create a new Project in the MPLAB X IDE
Select the PIC16F18855 microcontroller
Create new source files in the project directory using repository files
Compile and flash with debugger when ready

Initialization

Communication is made to PCU via UART protocol. The UART Module and Interrupts are initialized for asynchronous serial communication.

Clock Frequency = 32Mhz

Figure 2 - Baud Rate Formula

SP1BRG = 68

TX1STAbits.SYNC = 0; // Async Mode

TX1STAbits.BRGH = 1; // High-speed baud rate
BAUD1CONbits.BRG16 = 1;

TX1STAbits.TXEN = 1; // Transmitter and Receiver enabled
RC1STAbits.SPEN = 1;    
RC1STAbits.CREN = 1;

SP1BRGH = 68 // Baud Rate for 115200

// Enable interrupts
PEIE = 1;
GIE = 1;
PIR3bits.RCIF = 0;
PIE3bits.RCIE = 1;

Communication with PCU via payload messages

Bytes 1 & 2 - Sync Bytes
Bytes 3 & 4 - Type of Message
Bytes 5 & 6 - Payload Size

Usage Example:

void send_set_pcu_info()
{
    for (int i = 0; i < 9; i++) {
        TX1REG = set_pcu_info[i];
        while (!TX1STAbits.TRMT) {} // wait until register is empty
    }
}

Get PCU Info Command

volatile uint8_t get_pcu_info[6] = {0xFE, 0x19, 0x01, 0x04, 0x00, 0x00};

PCU Info Respsone
12 byte buffer

response = [
SYNC1,
SYNC2,
ID_LSB,
ID_MSB,
SIZE_LSB,
SIZE_MSB,
TEAM_ID,
PLAYER_ID,
HEALTH_LSB,
HEALTH_MSB,
SHIELD_FLAG,
REPAIR_FLAG
]

Set PCU Info Command

volatile uint8_t set_pcu_info[9] = {0xFE, 0x19, 0x03, 0x04, 0x03, 0x00, TEAM_ID (##h), PLAYER_ID (##h), DEVICE_ID (##h)};

TEAM_ID - Team number in hexadecimal
PLAYER_ID - Group number in hexadecimal
DEVICE_ID - 1 for Rover, 2 for Harvester

Get Flysky Info Command / Get User Data Command

volatile uint8_t get_flySky_info[6] = {0xFE, 0x19, 0x01, 0x05, 0x00, 0x00};

PCU Flysky Info Respsone
26 byte buffer

response = [
SYNC1,
SYNC2,
MSG_ID_LSB,
MSG_ID_MSB,
PAYLOAD_SIZE_LSB,
PAYLOAD_SIZE_MSB,
RJ_X_LSB,    // Right X Joystick
RJ_X_MSB,
RJ_Y_LSB,    // Right Y Joystick
RJ_Y_MSB,
LJ_Y_LSB,    // Left Y Joystick
LY_Y_MSB,
LJ_X_LSB,    // Left X Joystick
LJ_X_MSB,
SWITCH_A_LSB, // Switches
SWITCH_A_MSB,
SWITCH_B_LSB,
SWITCH_B_MSB,
SWITCH_C_LSB,
SWITCH_C_MSB,
SWITCH_D_LSB,
SWITCH_D_MSB,
POTEN_VRA_LSB,    // Potentiometer VRA
POTEN_VRA_MSB,
POTEN_VRB_LSB,    // Potentiometer VRB
POTEN_VRB_MSB,
]

Set Motor Settings Command

volatile uint8_t set_motor_settings[10] = {0xFE, 0x19, 0x01, 0x06, 0x04, 0x00, DIRA, PWMA, DIRB, PWMB};

DIRA - Motor A Directions: 0 - Brake, 1 - Forward, 2 - Backward
DIRB - Motor B Directions:
PWMA - Pulse Width Modulation A: 0 - 100
PWMB - Pulse Width Modulation B

Special Usage:

void send_motor_settings(uint8_t dirA, uint8_t pwmA, uint8_t dirB, uint8_t pwmB)
{
    uint8_t msg[10] = {0xFE, 0x19, 0x01, 0x06, 0x04, 0x00, dirA, pwmA, dirB, pwmB};

    for (uint8_t i = 0; i < 10; i++) {
        TX1REG = msg[i];
        while (!TX1STAbits.TRMT) {}
    }
}

Set Laser Scope Command

volatile uint8_t set_laser_scope[7] = {0xFE, 0x19, 0x01, 0x08, 0x01, 0x00, ENABLE};

ENABLE - 1 or 0 (On or Off)

Shoot Laser Command

volatile uint8_t shoot_laser[7] = {0xFE, 0x19, 0x01, 0x09, 0x01, 0x00, TYPE};

TYPE - 1 or 2 (Low Caliber or High Caliber)

Shoot Laser (Request Repair Code)

volatile uint8_t request_repair[6] = {0xFE, 0x19, 0x03, 0x09, 0x00, 0x00};

Shoot Laser (Transmit Repair Code)

volatile uint8_t transmit_repair[6] = {0xFE, 0x19, 0x04, 0x09, 0x00, 0x00};

Surface Exploration Command

volatile uint8_t set_surface_exploration[10] = {0xFE, 0x19, 0x01, 0x0A, 0x04, 0x00, TASK_ID_LSB, TASK_ID_MSB, TASK_SPECIFIC_VALUE_LSB, TASK_SPECIFIC_VALUE_MSB};

Task IDs:

1 - RFID
2 - Fundamental Frequency

Special Usage:

void send_surface_exploration(uint16_t task_id, uint16_t task_value)
{
    uint8_t msg[10] = {
        0xFE, 0x19,
        0x01, 0x0A,
        0x04, 0x00,
        (uint8_t)(task_id & 0xFF),
        (uint8_t)((task_id >> 8) & 0xFF),
        (uint8_t)(task_value & 0xFF),
        (uint8_t)((task_value >> 8) & 0xFF)
    };

    for (uint8_t i = 0; i < 10; i++) {
        TX1REG = msg[i];
        while (!TX1STAbits.TRMT) {}
    }
}

Subsystems

RFID Sequence

Using SPI communication, the RC522 antenna is turned on so that it can detect nearby RFID tags. A request (REQA) command is sent to check if any RFID card is present. If present, it responds with an ATQA (Answer to Request). An anti-collision command is sent to retrieve the card's UID. Error Checking is finally done to verify the UID of the card.
SPI Pins:

CS - RB2
SCK - RB3
MOSI - RB4
MISO - RB5
RST - RA1

uint8_t RC522_Anticollision(uint8_t *uid4, uint8_t *bcc)
{
    uint8_t cmd[2] = { PICC_ANTICOLL, PICC_ANTICOLL_NV };
    uint8_t resp[5];
    uint8_t bitLen = 0;
    uint8_t status;
    uint8_t calcBcc;

    status = RC522_Transceive(cmd, 2, resp, &bitLen, 0x00);
    if (status != RC522_OK) return status;

    if (bitLen != 40) return RC522_ERR_PROTOCOL;

    uid4[0] = resp[0];
    uid4[1] = resp[1];
    uid4[2] = resp[2];
    uid4[3] = resp[3];
    *bcc    = resp[4];

    calcBcc = uid4[0] ^ uid4[1] ^ uid4[2] ^ uid4[3];
    if (calcBcc != *bcc) return RC522_ERR_BCC;

    return RC522_OK;
}

rfid.c

Optical Signal Decoding

Using I2C communication, the APDS9960 color sensor is initialized and reads red, green, blue and clear light values from its registers. The sensor data is combined into 16-bit values for each color channel. Based on the dominant color, a note from the buzzer is played.

Red - C4
Green - F4
Blue - A4

I2C Pins:

SCL - RC3
SDA - RC4

void DelayMicroseconds(uint16_t us) 
{
    while(us--) {
        NOP();
        NOP();
        NOP();
        NOP();
    }
}

void PlayC4(uint16_t duration_ms)
{
    ANSELBbits.ANSB1 = 0;
    TRISBbits.TRISB1 = 0;

    uint16_t half_period = 1104;
    uint32_t cycles = ((uint32_t)duration_ms * 1000UL) / (half_period * 2UL);

    for (uint32_t i = 0; i < cycles; i++) {
        LATBbits.LATB1 = 1;
        DelayMicroseconds(half_period);

        LATBbits.LATB1 = 0;
        DelayMicroseconds(half_period);
    }
}

optical.c

Solar Array

The Solar Array Activation module is designed to provide sufficient illumination to a solar panel to charge it. It uses a C512A-WNN-CZ0B0151-ND LED and a 2N7000 MOSFET to drive voltage making the LED brighter. After directing sufficient light to the panel, its connected gate will open.
LED Controlling Pin: RB0

Alien Frequency

The PIC measures an input signal from the SPW2430 mic using the ADC and stores 128 samples at a fixed sampling rate. It then calculates the average signal level and checks the signal amplitued to make sure a valid waveform is present. To find fundamental frequency, an AMDF (Amplitude Magnitude Difference Function) is used. It compares the signal to delayed versions of itself over a range of tau, and looks for the first strong minimum. A small parabolic interpolation is then applied to improve accuracy.
Analog Input Pin: RA0

void SPW_sample() {
    uint8_t i, tau;
    uint32_t sum = 0;
    int16_t mean;
    
    for (i = 0; i < SAMPLE_COUNT; i++) {
        adc_buffer[i] = ADC_Read();
        sum += adc_buffer[i];
        __delay_us(SAMPLE_PERIOD_US);
    }
    mean = (int16_t)(sum / SAMPLE_COUNT);

    uint16_t max_val = 0;
    uint16_t min_val = 1023;
    for (i = 0; i < SAMPLE_COUNT; i++) {
        if (adc_buffer[i] > max_val) max_val = adc_buffer[i];
        if (adc_buffer[i] < min_val) min_val = adc_buffer[i];
    }

    if ((max_val - min_val) < MIN_PEAK_AMPLITUDE) {
        current_hz = 0;
        LATAbits.LATA1 = 0;
        __delay_ms(50);
        //continue;
    }

    // AMDF Analysis
    uint8_t found_tau = 0;
    uint32_t s_prev, s_curr, s_next;

    s_prev = compute_amdf(MIN_TAU - 1, mean);
    s_curr = compute_amdf(MIN_TAU, mean);

    for (tau = MIN_TAU; tau < MAX_TAU; tau++) {
        s_next = compute_amdf(tau + 1, mean);

        if (s_curr < s_prev && s_curr <= s_next) {
            // Depth check
            if ((s_prev - s_curr) > (s_curr / LOCAL_MIN_MARGIN_DIV)) {
                found_tau = tau;

                // Parabolic Interpolation for Sub-Integer Accuracy
                float delta = (float)((int32_t)s_prev - (int32_t)s_next) /
                              (2.0f * (float)(s_prev + s_next - 2 * s_curr));

                float exact_tau = (float)found_tau + delta;
                current_hz =
                    (uint16_t)((float)SAMPLE_RATE_HZ / exact_tau) - 110;
                if (current_hz > 1000 && current_hz < 2000)
                    current_hz -= 100;
                else if (current_hz > 2000 && current_hz < 3000)
                    current_hz -= 350;
                else if (current_hz > 3000)
                    current_hz -= 500;
                break;
            }
        }
        s_prev = s_curr;
        s_curr = s_next;
    }
    __delay_ms(20);
}

microphone.c

Flysky Controls

The Flysky transmitter acts as the main interface for switching between sensing modes, movement and communication tasks.
main.c

Figure 3 - Rover Movement Demo

Figure 4 - Flysky Diagram

Channel	Control	Operator Action	Rover Response
1	Right Joystick Y	Forward / Back	Moves Forward or Backward.
2	Right Joystick X	Request Repair Code and Transmit Repair Code	Furthest Left to request repair code and Furthest Right to transmit repair code.
3	Left Joystick Y	Get User Info	Request User Info
4	Left Joystick X	Left / Right	Turns Left or Right (Skid Steering).
5	Switch A	Solar Array Toggle	Turns on LED for Solar Array
6	Switch B	Frequency Capture	Starts audio recording for signal frequency capture.
7	Switch C (3-pos)	Pos 1 – Idle (No function) / Pos 2 – Optical Decoding / Pos 3 – RFID Gate	Switches between idle, Optical Decoding and RFID Gate
8	Switch D	Laser Toggle	Turns on auto firing laser.
9	VRA	Send RFID Gate UID	Send RFID digits to homebase.
10	VRB	Send Freq Value	Send Fundamental Freq to homebase.

Table 1 - Flysky controls

Name		Name	Last commit message	Last commit date
Latest commit History 109 Commits
images		images
.gitignore		.gitignore
LICENSE		LICENSE
README.md		README.md
config.h		config.h
init.h		init.h
main.c		main.c
microphone.c		microphone.c
optical.c		optical.c
pcu.c		pcu.c
rfid.c		rfid.c
uart_init.c		uart_init.c

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Repository files navigation

Harvest Rover

Hardware:

Software:

Setup

Initialization

Communication with PCU via payload messages

Usage Example:

Get PCU Info Command

Set PCU Info Command

Get Flysky Info Command / Get User Data Command

Set Motor Settings Command

Special Usage:

Set Laser Scope Command

Shoot Laser Command

Shoot Laser (Request Repair Code)

Shoot Laser (Transmit Repair Code)

Surface Exploration Command

Special Usage:

Subsystems

RFID Sequence

Optical Signal Decoding

Solar Array

Alien Frequency

Flysky Controls

About

Uh oh!

Releases 1

Packages

Uh oh!

Contributors

Uh oh!

Languages

Folders and files

Latest commit

History

Repository files navigation

Harvest Rover

Hardware:

Software:

Setup

Initialization

Communication with PCU via payload messages

Usage Example:

Get PCU Info Command

Set PCU Info Command

Get Flysky Info Command / Get User Data Command

Set Motor Settings Command

Special Usage:

Set Laser Scope Command

Shoot Laser Command

Shoot Laser (Request Repair Code)

Shoot Laser (Transmit Repair Code)

Surface Exploration Command

Special Usage:

Subsystems

RFID Sequence

Optical Signal Decoding

Solar Array

Alien Frequency

Flysky Controls

About

Resources

License

Uh oh!

Stars

Watchers

Forks

Releases 1

Packages 0

Uh oh!

Contributors

Uh oh!

Languages

Packages