How to use C with a Raspberry Pi servo HAT?

Ngang · July 26, 2016, 11:29am

Hi, I’ve been working on a project not entirely FRC related but I was hoping someone would have some advice.

It’s my first time working with Raspberry Pi, but my team wants to try and use them and ROS to control a large group of robots with C, but it doesn’t seem like C is really supported by that many libraries with the HAT. Are there other programming languages more viable for this? Does anyone have any experience with the HAT and C?

Andrew_Lobos · July 26, 2016, 11:39am

I ported the Adafruit servo HAT library to C++ for a personal project a while ago. Worked great for driving a few victors on a small robot. This is the HAT I used: https://www.adafruit.com/products/2327

Here’s the source: https://github.com/4ndr3w/PiBot/blob/e81e369494136ceea5d1d556b484e47e470a2e11/drivers/PWM.cpp

github.com

4ndr3w/PiBot/blob/e81e369494136ceea5d1d556b484e47e470a2e11/drivers/PWM.h

#ifndef PWM_h
#define PWM_h

#include <wiringPiI2C.h>
#include <time.h>
#include <math.h>

enum PWMConstant {
    __MODE1              = 0x00,
    __MODE2              = 0x01,
    __SUBADR1            = 0x02,
    __SUBADR2            = 0x03,
    __SUBADR3            = 0x04,
    __PRESCALE           = 0xFE,
    __LED0_ON_L          = 0x06,
    __LED0_ON_H          = 0x07,
    __LED0_OFF_L         = 0x08,
    __LED0_OFF_H         = 0x09,
    __ALL_LED_ON_L       = 0xFA,
    __ALL_LED_ON_H       = 0xFB,

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You’ll need to link it with the WiringPI library.

Also be very careful if you’re driving a large robot like this - if your program crashes/exits, the servo hat will keep outputting the last PWM value it was set at.

Ngang · July 26, 2016, 11:58am

Thanks!