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Digital Thermometer

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    DIGITAL THERMOMETER    

    RAJ K. GORKHALI

    This digital thermometer can measure temperatures up to 150C with an accuracy of +_1C. The temperature is read on a 1V full scale-deflection (FSD) moving-coil voltmeter or digital voltmeter.

    Operational amplifier IC 741 (IC3) provides a constant flow of current through the base-emitter junction of npn transistor BC108 (T1). The voltage across the base-emitter junction of the transistor is proportional to its temperature. The transistor used this way makes a low-cost sensor. You can use silicon diode instead of transistor. The small variation in voltage across the base-emitter junction is amplified by second operational amplifier (IC4), before the temperature is displayed on the meter. Preset VR1 is used to set the zero-reading on the meter and preset VR2 is used to set the range of temperature measurement.

    Operational amplifiers IC3 and IC4 operate off regulated +_5V power supply, which is derived from 3-terminal positive voltage regulator IC 7805 (IC1) and negative low-dropout regulator IC 7660 (IC2). The entire circuit works off a 9V battery.

    Assemble the circuit on a general-purpose PCB and enclose in a small plastic box. Calibrate the thermometer using presets VR1 and VR2. After calibration, keep the box in the vicinity of the object whose temperature is to be measured. 



     

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    Post Comment | 37 Comments



    Sheshank   995 days ago

    plzzzz give more info on collector of the transistor
    Reply   1 Reply
    Noname   820 days ago

    BC108 use as sensor Dont connect to anything... only for act like diode
    Reply  
    Pran   980 days ago

    Connect the collector to the posetive rail red above.
    Reply  
    pooja   971 days ago

    exactly which meter should be uselike according to ms raj...the output is to be measure on 1v FSD moving coil or digital voitmeter...so i tired by using multimeter....my question is is it fine by using multimeterand i used 22n ceramic capacitor instead of 220nF at input sideplzz reply sooon.....
    Reply   1 Reply
    Ganesh   960 days ago

    As per ckt diagram 220nf capacitor is comnnected accross input and common & it should be for rectifying the high frequency transient comming in the input. so no matter if u use 22nf instead of 220nf. but i suggest if ur ckt works slowly then we recommend that use the 220nf.
    Reply  
    DEEP JYOTI   966 days ago

    HOW CAN I ORDER RHIS PROJECT???????????
    Reply  
    Sagarmothkurigmail.com   959 days ago

    Hello im a btech student and id like to know abt transistor in detail...like i mean pls explain me in general not as per text
    Reply  
    Sameer   952 days ago

    hey i implemented the circuit on bread board but how to measure the temperature???multimeter shows the voltagehow do we find temperature of the particular object??
    Reply  
    pooja   945 days ago

    by using multimeter i got d output in terms of voltage so.....how to convert it into temperature??????reply soooon...............
    Reply  
    Anuja   941 days ago

    exactly.. i too got its output in terms of voltage.. hw to convert it in temperature....?? ways d callibration..?
    Reply   1 Reply
    harishankar   918 days ago

    for the calibration use an adc circuit
    Reply   1 Reply
    nikhil   812 days ago

    Its better to make thermometer using ICL 710706 Ic and LM-35.Lm-35 having 0.1vc temp. coefficient and using this we can easily interface ICL 7107 with LM-35 without any micro controller...
    Reply   1 Reply
    Efy Admin   812 days ago

    This is another way of designing the circuit
    Reply  
    laxminarayan   939 days ago

    Absolutely waste of money Inserting the sensor in ice and boiling water shows nearly same reading
    Reply   1 Reply
    davis   804 days ago

    it does not provide exact reading as like this
    Reply  
    lucky jain   934 days ago

    this is a working project or nt giving nly 1 reading i.e. .779 v
    Reply   1 Reply
    sriram   846 days ago

    how it will show the temperature....... u say its a digital thermometer........
    Reply  
    ankit goyal   890 days ago

    by using multimeter i got d output in terms of voltage so.....how to convert it into temperature??????reply soooon..
    Reply   1 Reply
    ankit ror   801 days ago

    u can measure its resistanse by using multimeter and than u can change it in c for ex. as resistance is 125 then we calculate 100-12525 after that 255262.5c
    Reply  
    Nandadeep   846 days ago

    the collector teminal should be left open..them am getting voltage in terms of millivolts...if 1vis fsv of 150c then one degree comes out to be 6.6mv..but at the start only am getting 0.8v ...there is some serious calibration issue...plz enlighten me on it..
    Reply  
    pranav   845 days ago

    worst information
    Reply  
    dhivya   844 days ago

    how to convert voltage to temperature?
    Reply  
    rohit singh   840 days ago

    this is good for project work ..........but there not give sufficient info.
    Reply   1 Reply
    anil kumar verma   238 days ago

    hi i am anil.i make project for btech students based on microcontroller like atmega-16atmega-880518052 etc.if want to make any project for final year. i will do it for you in reasonable price kindly contect to at my mail id741555timer@gmail.com
    Reply  
    siddharth   828 days ago

    this is exelent for project.........
    Reply  
    vignesh   827 days ago

    how many cost for this eqiupment
    Reply  
    mangeshkar   813 days ago

    DIGITAL THERMOMETER in digitial thermomemter we use lcd or led display on the output thermometer than its look nice . afterthat it should be both c & f that its also nice.
    Reply  
    mangeshkar   813 days ago

    DIGITAL THERMOMETER in digitial thermomemter we use lcd or led display on the output thermometer than its look nice . afterthat it should be both c & f that its also nice.
    Reply  
    kkk   813 days ago

    how to read the temperature i m getn the op in terms of voltage.
    Reply  
    SHAIKRAFI   800 days ago

    sirpllzz tell me how much it cost & mention the components in detail.
    Reply  
    Priyank Bhanot   793 days ago

    why do we use zener diode here as load?why not ne resistor?
    Reply   1 Reply
    Efy Admin   792 days ago

    Zener diode is not a load here, it is used to limit the out voltage to 4.7V
    Reply  
    GAUTAM SHRIVAS   789 days ago

    how can change voltage into temperature
    Reply   1 Reply
    Shriram   568 days ago

    For measuring the Exact temperature with an accuracy of 0.1 C I have used a LM 35 Temperature sensor and the circuit is here httpshriramscircuits.wordpress.com
    Reply  
    SILENT ANAND   769 days ago

    very supper sir
    Reply  
    jaymin patel   754 days ago

    I dont see the use of zener diode can any one explain the use of ZD1 i.e. zener diode
    Reply  
    DEEP   206 days ago

    by using multimeter i got d output in terms of voltage so.....how to convert it into temperature??????reply soooon...............
    Reply  

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