APC Australia - September 2019

howto»raspberry pi masterclass

T

hisissuewe’lllearnhowtouse

theExplorerHATProtowork

withanalogueelectronicsby

creatingtwoprojects.First we

createasimplelight-detecting

nightlight,thenwecreatean

electroniccandlethatwecanblow

out.Butfirstweneedtosetupour

equipment.

Withthepowerturnedofftoyour

RaspberryPi,placetheExplorerHAT

Prosothatitconnectstoall 40 GPIO

pins,andsothatitfitsneatlyabovethe

Pi.Nowconnectyourkeyboard,mouse,

HDMIandsoontoyourPiandbootup.

Forthenextstepyouwillneedto

connecttotheinternetusingWi-Fior

Ethernet.Onceconnected,opena

terminal,theiconforwhichisfound in

thetopleftofthescreen.Inthe

terminaltypethefollowingto

automaticallyinstallandconfigure

theExplorerHATProsoftware:

$ curl https://get.pimoroni.

com/explorerhat | bash

Duringtheinstallyouwillbeasked

toconfigureI2Candtoinstallexample

codewhichyoucangetfromhttp://bit.

ly/lxf252pihat.Answeryestothese

questions.Onceinstalled, close the

terminalwindow.

PROJECT1:NIGHTLIGHT

Tointroduceanalogueelectronicswe

shallusethemostsimpledevice,alight

dependentresistor(LDR).This

componentchangesresistancebased

onlightlevels.Forthisprojectweshall

placetheLDRonthebreadboardand

connectonelegto3.3V,andtheother

toGNDviathe22Kohmresistor.Then

weconnectAnalog 1 fromtheboardto

thesamelineasourresistorandLDR.

Wedothisasitcreatesavoltage

dividerthatweusetomeasurethe

lightlevelasavoltage.Seethediagram

inthedownloadforanaccurate

reference.

Wenowmoveontothecode.Using

yourfavouriteeditor(IDLE,Mu,

Thonny)createanewfileandthensave

thatnewfileasnightlight.py.

Remembertosaveoften!Westartthe

codewithtwoimportedlibraries,

time and explorerhat ,whichwe

renameto eh forbetterconvenience.

import time

import explorerhat as eh

Using analogue

HAT interfaces

Les Pounder showsustwomore projects using the deceptively simple

Explorer HAT Pro – and a little Python code.

Thenwecreatealoop to constantly

runourcode.

while True:

Let’stakealightlevelreadingand

storeitinsideavariablecalled light

• thiswillshowthevoltagethatour
  circuitisproducingbasedonthe
  resistanceleveloftheLDR.Thisis
  printedtothePythonshellfordebug.
  light = eh.analog.one.
  read()
  print(light)
  Wethenuseaconditionaltestthat
  checkstoseeifthevoltagedetectedis
  lessthan2V.Ifthatisthecasethenit
  mustbegettingdark,sothefourLEDs
  ontheExplorerHATProwillturn on.
  if light< 2.0:
  eh.light.on()
  Butifitdaylightthenthevoltage
  willbeover2Vandsothe else
  conditionactivatesand turns off the
  ExplorerHATLEDs.
  else:
  eh.light.off()
  Savethecodeandwhenready,runit.
  CovertheLDRwithyourhandandthe
  LEDsshouldlightup;moveitandthe
  LEDsturnoff.Ifyouneedtotweakthe
  values, take a look at the Python shell

toseewhatvoltagechangesthereare

whenthesensordetectsdarkness.

PROJECT2:ADIGITALCANDLE

ThisprojectisinspiredbytheNintendo

DS,specificallyasectioninTheLegend

ofZelda:PhantomHourglasswhereyou

areinstructedto‘blowout’fire/torches

inthegame.Todothisweblowonto

theconsoleandthegamereacts.In

realityweareblowingontoa

microphoneandananaloguesignalis

beingmeasuredtoactasatrigger.To

replicatethisweshallcontroltheLEDs

presentontheExplorerHATProusing

amicrophoneboard.Themicrophoneis

connectedtoourExplorerHATProas:

GND>GND,OUT>Analog 1 andVCC>

5V.

Wenowmoveontothecode.Createa

newfileasbeforeandthensavethat

newfileascandle.py.Thefirstthree

linesofourPythoncodeimport

prewrittenlibrariesofcode.Thefirstis

called time andweusethatto

controlthespeedofourproject.Next

weimportthe explorerhat library,

butrenameitto eh foreaseofuse.

Lastlyweimportthe random library

which will be used for our candle

Thissimplecircuitof fersagreatintroduction

toanalogueelectronics.Itrequiresonlyafew

cheap components and is accessible to all.