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2.1.9 Joystick(MCP3008)

Note

Depending on your kit version, please identify whether you have ADC0834 or MCP3008 and proceed with the matching section.

Introduction

In this project, We’re going to learn how joystick works. We manipulate the Joystick and display the results on the screen.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
Joystick Module	-
MCP3008	-

Schematic Diagram

When the data of joystick is read, there are some differents between axis: data of X and Y axis is analog, which need to use MCP3008 to convert the analog value to digital value. Data of Z axis is digital, so you can directly use the GPIO to read, or you can also use ADC to read.

Experimental Procedures

Step 1: Build the circuit.

Step 2: Go to the folder of the code.

cd ~/raphael-kit/c/2.1.9-2/

Step 3: Compile the code.

gcc 2.1.9_Joystick.c -o joystick -lwiringPi

Step 4: Run the executable file.

./joystick

After the code runs, turn the Joystick, then the corresponding values of x, y, Btn are displayed on screen.

Note

If it does not work after running, or there is an error prompt: "wiringPi.h: No such file or directory", please refer to Install and Check the WiringPi.

Code

#include <wiringPi.h>
#include <wiringPiSPI.h>
#include <stdio.h>

#define SPI_CHANNEL 0
#define SPI_SPEED   1000000  // 1 MHz
#define BtnPin      3        // WiringPi 3 = BCM GPIO22

// Read from MCP3008 channel (0–7)
int read_ADC(int channel) {
    if (channel < 0 || channel > 7) return -1;

    unsigned char buffer[3];
    buffer[0] = 1;                            // Start bit
    buffer[1] = (8 + channel) << 4;           // Channel config
    buffer[2] = 0;

    wiringPiSPIDataRW(SPI_CHANNEL, buffer, 3);

    int result = ((buffer[1] & 0x03) << 8) | buffer[2];
    return result;
}

int main(void) {
    if (wiringPiSetup() == -1) {
        printf("WiringPi setup failed!\n");
        return 1;
    }

    if (wiringPiSPISetup(SPI_CHANNEL, SPI_SPEED) == -1) {
        printf("SPI setup failed!\n");
        return 1;
    }

    pinMode(BtnPin, INPUT);
    pullUpDnControl(BtnPin, PUD_UP);

    while (1) {
        int x_val = read_ADC(0);     // VRX on CH0
        int y_val = read_ADC(1);     // VRY on CH1
        int btn_val = digitalRead(BtnPin);  // SW button

        printf("x = %d, y = %d, btn = %d\n", x_val, y_val, btn_val);
        delay(100);
    }

    return 0;
}

Code Explanation

1. This section initializes the libraries needed for GPIO and SPI communication.

   #include <wiringPi.h>
   #include <wiringPiSPI.h>
   #include <stdio.h>
   
   #define SPI_CHANNEL 0
   #define SPI_SPEED   1000000  // 1 MHz
   #define BtnPin      3        // WiringPi 3 = BCM GPIO22
   

2. Defines a function read_ADC() to read analog data from MCP3008. It communicates over SPI to request data from a given channel (0–7), then parses the response to get a 10-bit ADC result.

   int read_ADC(int channel) {
       if (channel < 0 || channel > 7) return -1;
   
       unsigned char buffer[3];
       buffer[0] = 1;
       buffer[1] = (8 + channel) << 4;
       buffer[2] = 0;
   
       wiringPiSPIDataRW(SPI_CHANNEL, buffer, 3);
   
       int result = ((buffer[1] & 0x03) << 8) | buffer[2];
       return result;
   }
   

3. The main function initializes the WiringPi and SPI interfaces, configures the joystick’s button pin, and continuously reads joystick values and prints them to the console.

   int main(void) {
       if (wiringPiSetup() == -1) {
           printf("WiringPi setup failed!\n");
           return 1;
       }
   
       if (wiringPiSPISetup(SPI_CHANNEL, SPI_SPEED) == -1) {
           printf("SPI setup failed!\n");
           return 1;
       }
   
       pinMode(BtnPin, INPUT);
       pullUpDnControl(BtnPin, PUD_UP);
   
       while (1) {
           int x_val = read_ADC(0);     // VRX to CH0
           int y_val = read_ADC(1);     // VRY to CH1
           int btn_val = digitalRead(BtnPin);  // SW to GPIO22
   
           printf("x = %d, y = %d, btn = %d\n", x_val, y_val, btn_val);
           delay(100);
       }
   
       return 0;
   }
   

4. In this program:

   • The joystick’s VRX is connected to CH0 of MCP3008.

   • The VRY is connected to CH1.

   • The button (SW) is connected to GPIO22 (WiringPi pin 3).

   • The read_ADC() function is used to read analog values from VRX and VRY.

   • The digital value of the joystick button is read using digitalRead().

   • All values are printed continuously every 100 milliseconds.