Raspberry Pi 3 + GPIO pins (File System)
Example code of connecting the Raspberry Pi v3 to a LED light. I'm using the Linux file system to control the GPIO pins, which is probably not ideal. The resistor is 220 ohms.
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| // Raspberry Pi 3 with Blinking | |
| // Copyright (C) 2021 https://www.roboticboat.uk | |
| // c8b70e31-b78e-4f6c-9341-8b5a6c9d06f8 | |
| // | |
| // This program is free software: you can redistribute it and/or modify | |
| // it under the terms of the GNU General Public License as published by | |
| // the Free Software Foundation, either version 3 of the License, or | |
| // (at your option) any later version. | |
| // | |
| // This program is distributed in the hope that it will be useful, | |
| // but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
| // GNU General Public License for more details. | |
| // | |
| // You should have received a copy of the GNU General Public License | |
| // along with this program. If not, see <https://www.gnu.org/licenses/>. | |
| // These Terms shall be governed and construed in accordance with the laws of | |
| // England and Wales, without regard to its conflict of law provisions. | |
| #include <stdio.h> | |
| #include <string.h> | |
| #include <stdbool.h> // bool variable | |
| #include <unistd.h> // usleep | |
| #define HIGH true | |
| #define LOW false | |
| #define INPUT true | |
| #define OUTPUT false | |
| // Define function signatures | |
| void digitalWrite(FILE*, bool); | |
| FILE* pinMode(int, bool); | |
| // ================================================= | |
| // This script is working with the File System. | |
| // Advantage is that it works | |
| // Disadvantage is that it will be slow. Also limited by | |
| // the number of open files allowed. | |
| // ================================================= | |
| int main() | |
| { | |
| // Initialise the GPIO pin (OUTPUT or INPUT) | |
| FILE* greenPin = pinMode(4, OUTPUT); | |
| // Loop forever | |
| while(1){ | |
| // Turn on the LED | |
| digitalWrite(greenPin, HIGH); | |
| // Wait 500ms | |
| usleep(500000); | |
| // Turn off the LED | |
| digitalWrite(greenPin, LOW); | |
| // Wait 500ms | |
| usleep(500000); | |
| } | |
| // Never actually get here. Close the file | |
| fclose(greenPin); | |
| return 0; | |
| } | |
| FILE* pinMode(int pinNumber, bool setInputOutput) | |
| { | |
| // Allocate memory | |
| char buf[40] = {0}; | |
| // Create file pointer to the pin | |
| FILE* file_pin = fopen("/sys/class/gpio/export","w"); | |
| fprintf(file_pin,"%d", pinNumber); | |
| fclose(file_pin); | |
| // Define if the pin is an INPUT or OUTPUT | |
| sprintf(buf,"/sys/class/gpio/gpio%d/direction", pinNumber); | |
| file_pin = fopen(buf,"w"); | |
| if (setInputOutput) | |
| { | |
| fprintf(file_pin,"in"); | |
| } | |
| else | |
| { | |
| fprintf(file_pin,"out"); | |
| } | |
| // Close the file | |
| fclose(file_pin); | |
| // Set the value of the pin. | |
| // Notice that this file is left open to change value in the loop | |
| sprintf(buf,"/sys/class/gpio/gpio%d/value", pinNumber); | |
| file_pin = fopen(buf,"w"); | |
| return file_pin; | |
| } | |
| void digitalWrite(FILE* file_pin, bool setHigh) | |
| { | |
| // The function assumes the file is already open | |
| // This is done to save time | |
| if (setHigh) | |
| { | |
| // Turn-on LED | |
| fprintf(file_pin,"1"); | |
| } | |
| else | |
| { | |
| // Turn-off LED | |
| fprintf(file_pin,"0"); | |
| } | |
| // Update the file (without closing it) | |
| fflush(file_pin); | |
| } |