# [b]DIGITAL THERMOMETER (URGENT HELP NEEDED)[/b]

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#### godwin4real

##### New Member
Am kind of new to this forum, and I need your help.
I want you to put me through in my project which I am working on at the moment. I need to Design and construct a Digital thermometer, and I dont know how to go about it. Please kindly help me with a circuit diagram (Schematic) of a Digital Thermometer.

I also need some explanation on how to build it.

I'll be very grateful for all your supports and contribution.

Thanks,

Godwin.

#### k7elp60

##### Active Member
About the easiest way I know to build a digital thermometer is to use a national LM34 precision temp. sensor and feed it to a digital voltmeter, as
the ouput voltage from the sensor is millivolts equal to the temperature in
degrees F.

#### mozikluv

##### New Member
digi thermo

hi godwin,

as mention by k7elp you can try the LM34 for your temp. sensor. as an added info there are i believe 2 kinds of LM34, they are LM34CH in a TO-5 casing and LM34Z in a TO-92 casing. both are fahrenheit temp sensor. the LM35CH & LM35Z are centigrade sensors.

if the above items are not available there is another way of making a simple temp. sensor, that is if accuracy of temp. reading is not of utmost importance.

you can use the 2N2222A as your temp. probe configured to act like a diode. then feed the output to an op-amp like the 741, from the emitter connect it to the inverting input, from the base/collector connect to the non-inverting input thru a variable resistor. this variable resistor is used to adjust the output of the op-amp from 2 - 3v. connect your output to your DMM. whatever is your reading, multiply that by 100, you have your F* temp.

am sorry i cant post the schem, its lost somewhere, what am doing now is just look at my pcb. by the way am using this sensor to test the temp of a heatsink to check whether i have used the appropiate heatsink size.

hope this could help.

p.s. i almost forgot to mention, this device should have a 5v supply. if you are interested with this i could draw up the schem and post it here or thru email. :wink:

#### yamaraj

##### New Member

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