RPiRobot Guidelines

Getting Started

Get source code

git clone https://github.com/alkaza/RPiRobot.git

Update repository

git pull

Go to library directory

cd /home/pi/CityScience/src/lib

Cleanup static library (if changes were made to static library)

make clean

Compile static library

make all

Go to source directory

cd /home/pi/CityScience/src

Remove static library from working directory (if changes were made to static library)

sh /home/pi/CityScience/src/scripts/rmlib.sh
examples

Copy static library to examples directory

sh /home/pi/CityScience/src/scripts/cplib.sh
examples

Go to examples directory

cd /home/pi/CityScience/src/examples

Cleanup all programs (if changes were made to examples)

make clean

Compile all programs

make all

Compile one program

make sensor

Run the program

sudo ./sensor

Terminate the program

Ctrl-C

Tutorial

Sample code

#include <stdio.h>
#include <wiringPi.h>
#include "robot.h"

int main(void)
{
	setup();
	
	while (1) {
		/* Implement here */
	}

	return 0;
}

• stdio.h provides many standard library functions for file input and output
• wiringPi.h is a GPIO Interface library for the Raspberry Pi
• robot.h is a static library for the RPiRobot

Setup function

setup ();

• Must include to run once
• Allows to terminate the program with Ctrl-C
• Initializes WiringPi, ultrasonic sensor and dc motor driver

Infinite loop

while (1) {
	/* Your code */
}

• Put your main code here to run repeatedly

Calculate distance detected by ultrasonic sensor

calc_dist ();

• Recommended distance for obstacle avoidance: 4~20

Simple motor control

move (direction, speedA, speedB);

Motor control with gradual deceleration

move_slow (direction, speedA, speedB);

• Recommended speed range: 70~150

Direction modes

• FW – go straight
• BW – go back
• RIGHT – turn right
• LEFT – turn left

Advanced variables

Change until which speed to decelerate (70 by default)

min_speed = speed;

Check the previous direction taken

if (prev_dir == direction){
	/* Your code */
}

Low-level motor control

Set direction

setDir (direction);

Set speed

setSpeed (speedA, speedB);

Experiments

• Measuring distance
• Going forward and backward
• Turning right and left
• Synchronizing motors
• Obstacle avoidance

Example files : sensor.c motor.c motor_synch.c avoid.c avoid_alter.c

Working Principles

DC Motor Driver

PWM (pulse width modulation) allows us to adjust the average voltage value that controls the speed of motors. The technique is to turn the power ON and OFF at a fast rate. The average voltage depends on the duty cycle. Duty cycle is the amount of time the signal is ON versus OFF in a single period of time.

H-Bridge circuit contains four switching elements (transistors or MOSFETs), with the motor at the center. By activating two switches at a time we can change the direction of the current flow. That changes the rotation direction of the motor.

• Input1 and Input2 pins are used for controlling the rotation direction of the motor A.
• Input3 and Input4 pins are used for controlling the rotation direction of the motor B.
• EnableA and EnableB pins are used for enabling and controlling the speed of motors with PWM input.

Possible speed range : 0~255 PWM

State	EnA	In1	In2	In3	In4	EnB
Stop	0	x	x	x	x	0
Brake	1	0	0	0	0	1
BW	1	0	1	0	1	1
Left	1	0	1	1	0	1
Right	1	1	0	0	1	1
FW	1	1	0	1	0	1
Brake	1	1	1	1	1	1

Ultrasonic Sensor

We write HIGH to Trig (output) pin for 10 usec to generate the ultrasound. That sends out an 8 cycle sonic burst which will travel at the speed of sound. The sound wave travels to an object and bounces back. Echo (input) pin reads the sound wave travel time in microseconds.

• Speed of the sound = 34000 cm/sec (or 0.034 cm/usec)
• Time = distance / speed
• Distance = time * speed / 2

Possible distance range : 2~400 cm (3.3V)

Power Supplies

Raspberry Pi 3 - Power Bank

• Capacity : 5200mAh
• Output : 5V 2A

DC Motor Driver - AAx6 Battery Holder

• Capacity : 1.5V x 6 = 9V

Wiring Raspberry Pi 3 (Model B V1.2)

DC Motor Driver (L296N)

DC Motor Driver	Raspberry Pi 3	WiringPi	Remark
EnA	Physical Pin12	Pin1	PWM0
In1	Physical Pin13	Pin2
In2	Physical Pin15	Pin3
In3	Physical Pin29	Pin21
In4	Physical Pin21	Pin22
EnB	Physical Pin33	Pin23	PWM1
Gnd	Physical Pin39		Ground

Important : don't forget to connect Raspberry Pi GND to GND pin on the module to complete the circuit.

Ultrasonic Sensor (HC-SR04)

Ultrasonic Sensor	Raspberry Pi 3	WiringPi	Remark
Vcc	Physical Pin1		3v3 Power
Trig	Physical Pin16	Pin4
Echo	Physical Pin18	Pin5
Gnd	Physical Pin20		Ground

Important : use Raspberry Pi 3.3V supply pin instead of 5V for the sensor signal and Raspberry Pi GPIO voltages to match.