Hardware Reference
In-Depth Information
Decoupling capacitors
Battery
Servo
5V regulator
Potentiometer
Figure 4-12:
Servo experiment wiring diagram
UNDERSTANDING LINEAR REGULATORS AND THE L IMITS OF
ARDUINO POWER SUPPLIES
Whyisitnecessarytouseanexternalpowersupplywhencertainitems
requiremorecurrent?Therearefewreasons.TheI/Opinscannotsupply
morethan40milliamps(mA)each.BecauseaDCorservomotorcancon-
sumehundredsofmilliamps,theI/Opinsarenotcapableofdrivingthem
directly.Eveniftheywere,youwouldn'twanttobecauseofthedamagethat
canbecausedbyinductivevoltagespikes.
ItmakessensethatyouneedtouseanexternalsupplywithaDCmotor
becauseyouneedthehighervoltage,butwhydoesaservoneedanexternal
supplyifitisatthesamevoltageastheArduino?TheArduinogeneratesthe
5VusedforthelogiceitherdirectlyfromtheUSBorbyusingabuilt-inlinear
regulatorwiththeDCbarreljackasthesupplyvoltage.WhenyouuseUSB,
amaximumof500mAisavailabletotheArduinoandallitsperipherals,
becausethatiswhattheUSBspeciicationallows.Whenyouuseanexternal
supplyofsuficientcurrent,thebuilt-inregulatorcansupplyupto1ampto
thecomponentsonthe5Vrail.
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