DIY Digital Thermometer

This instructable will show you how to make a thermometer that displays the temperature of the air.

It's not the most accurate thermometer in the world, but for this price and the fact that it was homemade...

Step 1 Parts

You will need:

1x ATMega8
2x7 segment display
1x1800 ohm resistor
7x160ohm resistors
1x KTY-13-5 (temperature sensor)

Comments

[ertxz18]

Great tutorial, just one question: so you said its not very accurate, is it due to the sensor used or just the design itself?

[finalxxx37]

cool project!! Now, i'm trying to build it , but i'm not able to program C. If i use a LM35 sensor what is the formula for calculate the temperature? What resistor i have to use ?

[Gernerakos]

What is the ,,ATM mega 8

[kyismaster]

Its a ATMEL mega chip. This usually comes with the arduino platform. ( arduino uno ATM 328. the chip is ATM (atmel) 32 bit 8 ) ref: http://arduino.cc/en/Main/ArduinoBoardUno

[a_b_siddique]

I cant seem to find the sensor chip anywhere, is there any other name for it? Can you send me a link for where i can buy it from? Thanks.

[a_b_siddique]

Also is the 7 Segment Display and Anode or a Cathode one?

[marteloficina]

which supply voltage?

[godofal]

if ur saying its not that accurate, how should i think of that? like 5 degrees(celcius) or less than 1?

[DemonDomen]

I think it's something like +/- 2°C

[A.C.E.]

is there a way for this to be Fahrenheit? im no good at interpreting Celsius.. or programming microchips for that matter. never mind lol.

[DemonDomen]

Sure, you'd just have to convert the number, but you'd need 3 displays.

[diydept]

Very nice 5*,This capacitor is very familiar to me. Is it Iskra Slovenia?

[DemonDomen]

Sure is.

[achelblack]

hi.i went to the store today to purchase the atmega8..but they asked me 'what number?' and i didnt know what to say..help me please..what did they mean by that?

[geoper2]

from the picture he posted i see that he is using an ATMEGA8-16PU so thats wat u can buy

[achelblack]

hi..can i ask sumthing? can i use any type of atmega8 for this project?

[pipp]

ooo you used iskra capacitators :D i haven't seen them in years (and this is the first time on instructable)

[Livyo]

It's work whit an DS18B20 sensor ?

[albylovesscience]

thats brilliant im going to radio shack soon so how much did all the components cost

[circuit_question]

I've been trying to build this circuit and I had a number of questions. Does a ATMega8L work? Do you need to program this? I was wondering what "This part is optional" meant? Does this mean connect all of this together? I was trying to order the KTY-13-5 temperature sensor. The KTY135 surface mount temperature sensor kept popping up. This is extremely small and hard to use. Do you know of an equivalent sensor that is much easier to use? What does the Vcc arrow connect to from the diagram? What does GNDIC1 mean? And as for power, is 1 positive? I'm excited about this project. I'm hoping to get it to work. Any help would be much appreciated.

[DemonDomen]

I think that a ATMega8L should work and yes, you need to program it.

That optional part is for connecting a programmer, so you can program it.
I didn't mark the pins in the schematic, but they are like this (from 1 to 5): POWER, MOSI, MISO, SCK, RESET, GROUND.

The pins above are the pins from the programmer. I personally use the STK200/300. You can also buy an avr ISP programmer.

I know the sensor is surface mount. When I ordered it, I didn't know. Luckily I managed to solder it. I guess you could use any sensor of the same family. Check the datasheet, there are more models inside. They all change their resistance with temperature and use the same formula to calculate the temperature. The only thing you might need to change is the resistance at 25°C (it's in the source code (i think the name of the variable is r25)).

It was not the best idea to add both the power symbols and plugs into the schematic, it only makes it confusing. The Vcc arrow is supposed to indicate that a 5V power supply is connected to that wire. The GNDIC1 is normal ground (eagle named it like that).

Yes, pin 1 of the plug is positive.

I hope you'll make it. If you have any trouble, don't be afraid to ask. If I don't answer in a while, write me a PM.

[circuitmage]

How 'bout a shot of the back of the board? :)

[circuitmage]

Nice project. Gets a vote from me for application. +/- 1 deg accuracy is a must for work applications. I need to build one for work to check IC temps. Check my entry for similar display project!

[odiekokee]

What is your total component cost for the project?

[DemonDomen]

I think it is safe to say that I paid about 15€. But you should know that I had to pay something like 5 € for the avr -.-

[PKM]

Is that under the normal price? It certainly doesn't sound like much for a large uC.

Do you know how much heat the temperature sensor will stand up to? I'm looking for a circuit like this to monitor the running temperature of my (air-cooled) motorbike engine, but can't use a temperature sensor that will melt as soon as it hits 90^oC.

[DemonDomen]

I checked on ebay, they cost 1,50€. The datasheet says it can survive up to 150°C.

[PKM]

OK, cool, that's good to know. Still need to get set up with a programmer, stripboard, common components etc. Hey, how do you get euro symbols? When I try to put the sterling symbol, the site goes mad and won't let me post comments.

[DemonDomen]

I just press Alt + E. If you want to make your own programmer, you should build the STK200/300. That's what I'm using and so far it worked quite well.

[Kiteman]

Nice little project. You say it is "not very accurate" - how close to true is it? Also, quite a few people would find it useful if you included a layout for soldering the perf-board.

[zaketus]

With that thermistor accuracy would be about +-3% in 25C (about 75F) temperature. Accuracy might vary with different sensors or packages.

[DemonDomen]

I'll try to check the accuracy when I find the time. Expect it to be in 1-2 weeks. About the layout... There's a lot of wires under the board, but you can't see it on the pictures. There was no way to make it with less wires. I'll upload a pcb.