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Single Chip Temperature Data Logger Rajendra Bhatt Williamsburg, VA rajbex [@] yahoo.com Introduction A data logger is a device that records measurements over time. The measurements could be any physical variable like temperature, pressure, voltage, humidity, etc. This project describes how to build a mini logger that records surrounding temperature values. It has following features: • Uses just one 8‐pin chip, so very compact size circuit. • Temperature range: 0 to +125°C. • Can store up to 254 measurements. • Sampling interval options: 1 sec, 1 min, 10 min • Reset feature to clear all previous measurements. • Serial transfer of recorded measurements to a PC • Three tactile switches for user inputs and a LED indicator. Description The beauty of this project is that it uses just a single chip for logging. It is PIC12F683, an 8‐pin microcontroller from Microchip. PIC12F683 has six general‐ purpose I/O (GP0‐GP5, GP3 is input only) pins, and 2K x 14 Flash program memory with 256 bytes of internal EEPROM. Temperature will be measured with a DS1820 temperature sensor. DS1820 is a one‐ wire digital temperature sensor from Dallas Semiconductor (now MAXIM). The operating temperature range of the device is –55°C to +125°C with an accuracy of ±0.5°C over the range of –10°C to +85°C. The temperature sensor output is 9‐bit Celsius temperature measurement, and so the temperature resolution corresponds to the least significant bit, and which is 0.5°C. But in this project we will use only the most significant eight bits. Therefore, the temperature resolution will be 1°C. The measured temperatures will be recorded into the internal EEPROM memory of PIC12F683. The first location of the internal EEPROM will store the sampling interval of data logger. Sampling interval defines the time gap between two successive measurements. This project will have 3 options for sampling time: 1 sec, 1 min, and 10 min. These are user selectable. The second location of EEPROM will store the number of measurements recorded so far. And the remaining 254 EEPROM locations will store 8‐bit temperatures. So, using 10 min sampling interval, 254 bytes of EEPROM will provide data logging for 42 hours. The recorded measurements can be sent to PC at any time through a serial link at 9600 baud.

Single Chip Temperature Data Logger - Electronics-Lab · Single Chip Temperature Data Logger Rajendra Bhatt Williamsburg, VA rajbex [@] yahoo.com Introduction A data logger is a device

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Page 1: Single Chip Temperature Data Logger - Electronics-Lab · Single Chip Temperature Data Logger Rajendra Bhatt Williamsburg, VA rajbex [@] yahoo.com Introduction A data logger is a device

SingleChipTemperatureDataLogger

RajendraBhattWilliamsburg,VA

rajbex[@]yahoo.com

Introduction

Adataloggerisadevicethatrecordsmeasurementsovertime.Themeasurementscouldbeanyphysicalvariableliketemperature,pressure,voltage,humidity,etc.Thisprojectdescribeshowtobuildaminiloggerthatrecordssurroundingtemperaturevalues.Ithasfollowingfeatures:

• Usesjustone8‐pinchip,soverycompactsizecircuit.• Temperaturerange:0to+125°C.• Canstoreupto254measurements.• Samplingintervaloptions:1sec,1min,10min• Resetfeaturetoclearallpreviousmeasurements.• SerialtransferofrecordedmeasurementstoaPC• ThreetactileswitchesforuserinputsandaLEDindicator.

Description

Thebeautyofthisprojectisthatitusesjustasinglechipforlogging.ItisPIC12F683,an8‐pinmicrocontrollerfromMicrochip.PIC12F683hassixgeneral‐purposeI/O(GP0‐GP5,GP3isinputonly)pins,and2Kx14Flashprogrammemorywith256bytesofinternalEEPROM.

TemperaturewillbemeasuredwithaDS1820temperaturesensor.DS1820isaone‐wiredigitaltemperaturesensorfromDallasSemiconductor(nowMAXIM).Theoperatingtemperaturerangeofthedeviceis–55°Cto+125°Cwithanaccuracyof±0.5°Covertherangeof–10°Cto+85°C.Thetemperaturesensoroutputis9‐bitCelsiustemperaturemeasurement,andsothetemperatureresolutioncorrespondstotheleastsignificantbit,andwhichis0.5°C.Butinthisprojectwewilluseonlythemostsignificanteightbits.Therefore,thetemperatureresolutionwillbe1°C.ThemeasuredtemperatureswillberecordedintotheinternalEEPROMmemoryofPIC12F683.

ThefirstlocationoftheinternalEEPROMwillstorethesamplingintervalofdatalogger.Samplingintervaldefinesthetimegapbetweentwosuccessivemeasurements.Thisprojectwillhave3optionsforsamplingtime:1sec,1min,and10min.Theseareuserselectable.ThesecondlocationofEEPROMwillstorethenumberofmeasurementsrecordedsofar.Andtheremaining254EEPROMlocationswillstore8‐bittemperatures.So,using10minsamplinginterval,254bytesofEEPROMwillprovidedataloggingfor42hours.TherecordedmeasurementscanbesenttoPCatanytimethroughaseriallinkat9600baud.

Page 2: Single Chip Temperature Data Logger - Electronics-Lab · Single Chip Temperature Data Logger Rajendra Bhatt Williamsburg, VA rajbex [@] yahoo.com Introduction A data logger is a device

UserInputs

Therewillbethreetactswitchesforuserinputs,namelyStart,Stop,andSend/Reset.Thethreeswitcheswillbeabletoacceptthefollowing4userrequests.

1. Start:When‘Start’buttonispressed,dataloggingstarts.2. Stop:Oncethe‘Stop’buttonispressed,datarecordingwillstop.3. Send:TransferdatatoPCthroughserialport.4. Reset:Holdingthe‘Send’buttonfor2secormoreclearstheinternal

EEPROMmemory.

SamplingTimeSelection

Thesamplingintervalcanbeselectedas1sec,1min,or10minusingthesamethreeswitches.Supposeifweneed1minsamplingtime,firstturnOFFthepower,thenholdthe‘Stop’button,turnthepowerON,andwaittilltheLEDglows.OncetheLEDglows,releasethebutton,andthesamplingintervalwillbesetto1min.ThenewsetsamplingtimewillbeupdatedtoEEPROMlocation0sothatincaseofpowerfailure,theprevioussamplingtimewillberestored.Similarly,use‘Start’and‘Send’buttonsfor1sec,and10minsamplingintervalsrespectively.

LEDIndicator

Everytimetheuserpressesinputbuttons,LEDglowsforamomenttoindicatethattheinputisaccepted.ItalsoblinksthriceeverytimeEEPROMWriteoperationtakesplace.Italsoblinksatthebeginningwhenthepoweristurned‘ON’.ItalsoglowswhentheEEPROMmemoryisfull.

Page 3: Single Chip Temperature Data Logger - Electronics-Lab · Single Chip Temperature Data Logger Rajendra Bhatt Williamsburg, VA rajbex [@] yahoo.com Introduction A data logger is a device

CircuitDiagram

Thecompletecircuitdiagramforthisprojectisshownbelow.

ThesixI/OpinsofPIC12F683areassignedasfollows:

1.GP0(Pin7,I/P):ThispinwillbeusedtoreadthetemperaturevaluefromDS1820sensor.

2.GP1(Pin6,O/P):ThiswillbeusedforserialdatatransfertoaPC.

3.GP2(Pin5,O/P):LEDoutputpin.

4.GP3(Pin4,I/P):Send(tactileswitch)

5.GP4(Pin3,I/P):Stop(tactileswitch)

6.GP5(Pin2,I/P):Start(tactileswitch)

AsimpletransistorbasedlevelshiftingwillbeusedtoconverttheTTLvoltagefromPIC12F683toappropriateRS232levelforserialdatatransfertoPC.TherequirednegativevoltageisderivedfromPCRS232portpin3(Tx),whichremainsidleasnodatatransferoccursfromPCtoPIC.Isolderedallthecomponentsonageneral‐purposeprototypingboard.Besides,myfinishedproductrunson3‐AAAbatterieswithadiodeinseriesforreversepolarityprotection.Ialsohaveapowerswitchontheboard.ThePICusesinternaloscillatorat4MHz,andMCLRisdisabled.

Page 4: Single Chip Temperature Data Logger - Electronics-Lab · Single Chip Temperature Data Logger Rajendra Bhatt Williamsburg, VA rajbex [@] yahoo.com Introduction A data logger is a device

ListofComponents

• PIC12F683microcontroller• DS1820temperaturesensor• BC557NPNtransistor• Resistors:10K(4),4.7K(2),470Ohm(1)• Capacitor:10uF,50V(1)• LED(1)• Tactswitches(3)

Software

ThefirmwareiswritteninCandcompiledwithmikroCcompilerfromMikroElektronika.IusedthefreeversionofitbecauseourHEXoutputisgoingtobelessthan2K.ThedownloadlinkformikroCishttp://www.mikroe.com/eng/downloads/get/29/mikroc_pro_pic_2010_v380_setup.zip

The3userinputswitchesworkoninterrupt­on­changemode.Thatmeansanytimetheuserpressesanybutton,aninterruptisgeneratedexceptattimeswhenthemicrocontrollerisreadingtemperaturevaluesfromDS1820(whichisinstantaneous)andwhenitistransferringdatatoaPCthroughserialport.Theinterruptsaredisabledatthoseinstants.Thedatatransfertakesplaceat9600baudrate.YoucanwriteyourownsoftwaretoreceivedataonPCside,butIhaveusedtheHyperterminalapplicationforthispurpose.MyHyperterminalsettingsare

bps:9600,DataBits:8,Parity:None,StopBits:1,FlowControl:Hardware

Configuration:Internalclock@4MHz,MCLRDisabled,WDTOFF

Pictures:

Page 5: Single Chip Temperature Data Logger - Electronics-Lab · Single Chip Temperature Data Logger Rajendra Bhatt Williamsburg, VA rajbex [@] yahoo.com Introduction A data logger is a device

Thisishowmyfinishedproductlookslike.

TransferringdatatoPC

Page 6: Single Chip Temperature Data Logger - Electronics-Lab · Single Chip Temperature Data Logger Rajendra Bhatt Williamsburg, VA rajbex [@] yahoo.com Introduction A data logger is a device

Hyperterminalreceivingwindow


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