Hall Effect

Contents

Overview

Parts

Arduino microcontroller and carrier board

LiPo battery

Hall effect switch (see spec sheets below)

NOTE: There are two types of hall effect sensors in the electronics supply cabinet.

1) SS495B: An analog sensor that outputs a voltage between zero and the supply voltage. e.g. if Vsupply = 5V, when there is no magnetic field, it outputs 2.5V and then either 0 or 5v for north or south.

2) A3211/2 (not sure which): A switch, outputs 0v when there is magnetic field and Vsupply* when there isn't.

*Note! The Vsupply max for this is 3.5V so make sure to use a voltage divider to power it with a lower voltage than 5v.

General information about hall effect sensors:

http://bildr.org/2011/04/various-hall-effect-sensors/

Prepare the breadboard

http://bildr.org/blog/wp-content/uploads/2011/04/us1881.png

Program the Microcontroller

This is a code written by Brian Alvarez -- a hall effect sensor makes the mini-me follow a magnetic strip

//EVERY LINE THAT STARTS WITH // IS A COMMENT AND NOT CODE

//we are using the servo library to control servos.

//http://arduino.cc/en/Reference/Libraries for more info

#include <Servo.h>

//define variables we will use in the program

//feel free to change these as needed, they

//depend on your specific configuration

//set up the "servo" object, which comes from the

//included servo library (the #include... line)

Servo leftMotor;

//sets which pin the left motor is attached to

//pins 8 and 9 are the 2 servo attachment points located

//FURTHEST away from the actual arduino

#define leftMotorPin 9

//use this to help make sure you robot travels straight.

//It allows us to compensate for discrepencies in different

//motors, etc. Also, if your robot drives backwards,

//make this negative. If your robot spins or stuff like that, play

//around with the signs

const double leftMotorScaler = 0.5;

//leave this at 90 unless you have weird motors. If we tell the

//servos to run at "90" speed, they stay still. Less, they run

//backwards, more they run forward. This provides lots of

//flexibility for using different types of servos

const int leftZero = 90;

//all the same things for the right motor

Servo rightMotor;

#define rightMotorPin 8

const double rightMotorScaler = -0.5;

const int rightZero = 90;

//which pin is the hall effect sensor attached to?

//Refer to this diagram for how to wire up the sensor

//http://bildr.org/blog/wp-content/uploads/2011/04/us1881.png

//it is a slightly different sensor, but the wiring is the same

#define hallEffectPin 2 //feel free to change this as needed

//this set of code runs once

void setup()

  //tell the arduino its going to read from the hall effect sensor

  //instead of send power to it

  pinMode(hallEffectPin, INPUT);

  //set up the servos, tell them what pin to use

  leftMotor.attach(leftMotorPin);

  rightMotor.attach(rightMotorPin);

//this code loops infinitely

void loop()

  //this works by following the edge of the magnetic strip.

  //it essentially tries

  if(digitalRead(hallEffectPin) == HIGH) //we are ON the line

    //turn OFF the line to follow the edge of line

    //run the left motor forward (hence the +) slowly

    leftMotor.write(leftZero+(20*leftMotorScaler));

    //run the right motor forward slightly faster

    rightMotor.write(leftZero+(40*rightMotorScaler));

  else //we are off the line

    //turn onto the line to follow the edge of line

    //same as above, but turning the other direction

    leftMotor.write(leftZero+(40*leftMotorScaler));

    rightMotor.write(rightZero+(20*rightMotorScaler));