switches & whiskers on the Arduino

living with the lab

lever arm switches mounted to Arduino

© 2012 David Hall

living with the lab

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DISCLAIMER & USAGE

the switches

• long lever with three electrical terminals• can be wired as normally open (electricity flows only when switch pressed)• can be wired as normally closed (electricity stops flowing when switch pressed)• used with 0.183 inch quick disconnect terminals

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living with the lab

wiringwhen the switch is not pressed, electricity can pass through the normally closed (NC) path

when the switch is pressed, electricity can pass through the normally open (NO) path

use a digital input to sense when switch is on or off

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living with the lab

ANALOG

RESE

T3V

3

5V Gnd Vin 0 1 2 3 4 5

7 6 5 4 3 2 1 03 2 1 0 9 81 1 1 1AR

EFG

ND

DIGITAL

POWER

Arduino

10kW switch

switchstatus

voltage at pin 7

status ofdigital input 7

0V(no power applied)

5V(direct connection to power)

HIGH

LOW

closed(pressed)

open (not pressed)

digitalRead(7)

check status of pin 7 using . . .

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living with the lab

why the 10kΩ resistor?

ANALOG

RESE

T3V

3

5V Gnd Vin 0 1 2 3 4 5

7 6 5 4 3 2 1 03 2 1 0 9 81 1 1 1AR

EFG

ND

DIGITAL

POWER

Arduino

10kW switch

using a large resistance limits the current so that we don’t waste electricity

𝑃=𝑉 ∙ 𝐼=𝑉 2

𝑅=

(5𝑉 )2

10,000Ω=0.0025W=2.5mW

. . . any resistor will do, but there’s no sense in wasting power

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hooking things up on your robot

living with the lab

• space is tight, and it’s easy to break the quick disconnect terminals (can solder them if desired)

• connect wires to the common and normally open terminals on the switch

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toolsa wire stripper and some sort of crimping tool are needed (can also crudely crimp using a vise)

living with the lab

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completing the circuit on the breadboard

• to prevent wires from coming loose• to make it easier to see what’s going on (easier to troubleshoot)

living with the lab

try to keep the wiring tidy . . . violet leads go to +5V source

white and red leads provide digital input one 10kΩ resistor per switch is installed

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programmingthis program causes the built-in LED on pin 13 to turn on when the switch is pressed

living with the lab

int whisker1=0;

void setup(){ pinMode(7,INPUT); pinMode(13,OUTPUT);}

void loop(){ whisker1=digitalRead(7); if(whisker1== HIGH) // whisker1==HIGH if whisker pressed { digitalWrite(13,HIGH); } // turn LED on pin13 on else { digitalWrite(13,LOW); } // turn LED on pin13 off}

this is our first time to use if … else control (see next slide)

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if / elseif/else allows greater control over the flow of code than the basic if statement, by allowing multiple tests to be grouped together arduino.cc

living with the lab

if (x < 500) { // do Thing A } else if (x >= 1000) { // do Thing B } else { // do Thing C }

can use an unlimited number of else if blocks . . . or none, as in the program on the previous slide