Picture of DIY Miniature Thermometer

For just a couple of bucks and a few components you have laying around your work area you can build a min thermometer than fits in your pocket. The whole circuit sits nicely right on top of a 9v battery, and is connected to it with double sided tape. Changing batteries was never so easy!
I hope you enjoy the project and vote it for the contests!

Step 1: Mini Thermometer Demonstration

In case you were wondering why the LEDs are flashing multiple times on each flash it's because I'm using PWM to power the pins. 

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robodude951 year ago
Nice Instructable! Completed mine today...used the button to put the pin to LOW instead of HIGH though...skipped using a pull up resistor this way.
FoamboardRC (author)  robodude951 year ago
Dude that's awesome! Thanks for posting the pic! What did you do with the resistor? You connected the pin from 5v directly to the ATtiny pin?
Yeah...now when the button is pressed the pin goes low.
FoamboardRC (author)  robodude951 year ago
Nice, that makes sense, since you ground the pin. Thanks!
mrmerino1 year ago
Could I make it so that it blinks at me in binary? And in Celsius?
FoamboardRC (author)  mrmerino1 year ago
Why not?
FoamboardRC (author)  FoamboardRC1 year ago
To have it print out C˚ just take out the F˚ conversion.
Was kind of confused about the schematic.The rj45 threw me for a loop. Being not too smart in these things, I made my own diagram. Not sure if it is riight though/
Screenshot from 2013-11-02 02:39:19.png
FoamboardRC (author)  Computothought1 year ago
The RJ45 is just a name. I forgot to change it. Instead it should be ATtiny85. The pins are still the same. I think yours is correct.
jrburke991 year ago
I made my own such device recently, but it uses an IR LED to blink a warning single at me via an IR camera in my son's bedroom if it gets too hot or too cold. It also has a red LED that blinks out the temperature just as yours does. But I think my code simplifies the process a bit. You should try this out. Also, you should be able to run all of this off of a 3v button cell, saving you even more space and weight. Just make sure you look up the sleep functions for the ATtiny, and use it as much as possible. In my code, the "SleepyTime" function puts the MCU to sleep for a period of time (32=32ms, 5=.5seconds). For your device, you could easily make it sleep constantly, checking for a button press periodically. For example, sleep in .5 second intervals, checking for a button press in between. 

TensDigit = (int)Temperature / 10;  // Split the number up into 2 digits
OnesDigit = (int)Temperature % 10;

      if (TensDigit != 0) {
        for (int i=1; i<=TensDigit; i++) {  // Blink LED # times for tens digit
          digitalWrite(STATUSLEDPIN, HIGH);
          digitalWrite(STATUSLEDPIN, LOW);

      SleepyTime(1);  // Pause between the 2 digits

      if (OnesDigit != 0) {
        for (int i=1; i<=OnesDigit; i++) {  // Blink LED # times for ones digit
          digitalWrite(STATUSLEDPIN, HIGH);
          digitalWrite(STATUSLEDPIN, LOW);
FoamboardRC (author)  jrburke991 year ago
JrBurk thank you soo much I couldn't figure out how to make the 10s digit blink and the 1s. I asked a question in the forum but it wasn't answered so I turned to my own poor devices :D.

So I don't really understand what you are doing with the 10's and 1's digit would you please explain?

Ok so the sleeping time saves some power?

Yes I was gonna run it off 3v battery but I didn't have any around :(. No job, no money, lack of electronics.

Thanks I will be eagerly awaiting a reply.
I was thinking the same thing as jrburke99. In the code

TensDigit = (int)Temperature / 10; // Split the number up into 2 digits
OnesDigit = (int)Temperature % 10;

you need to know that % means mod or remainder, and (int)Temperature means that whatever the Temperature / 10 gives, make an integer with no decimal point.

In your video your thermometer reads 69°. In the first line a rolling solve would look like this:
•TensDigit = (int)Temperature / 10; //Start
•TensDigit = (int)69 / 10; //Fill Temperature with 69
•TensDigit = (int)6.9; //Divide 69 by 10, giving you 6.9, which is a double (has a tenths digit (9)
•TensDigit = 6; //Convert double to int, which does not have anything to the right of the decimal point

The second line is a bit more fun. Let's roll that:

•OnesDigit = (int)Temperature % 10; //Start
•OnesDigit = (int)69 % 10; //Fill Temperature with 69 OnesDigit = (int)9; //when you do that long form math from elementary school and your answer here would be 69÷10= 60 with a remainder of 9
•OnesDigit = 9; //Convert to an integer.

I have taught coding before and Modulo (mod in some languages, % in others http://en.wikipedia.org/wiki/Modulo_operation))

If you are not conferrable with Modulo, it works the same way as this:
•OnesDigit = Temperature-TensDigit*10; //Start
Which goes:
•OnesDigit = 69-6*10; //Fill in the numbers
•OnesDigit = 9; //Solve, using order of operations

Either way you now have TensDigit = 6 and OnesDigit = 9.
FoamboardRC (author)  traisjames1 year ago
Basically I don't know how to easily know how to say in code, "Flash LED (10s digit) times" without adding delays. Then when I add delays then that means I have to specifically make a block for each number.
Instead of saying "Flash LED (10s digit) times", you want to say "Flash LED once 10s digit times". Thats where this block comes in:

for (int i=1; i<=TensDigit; i++) {  // Blink LED # times for tens digit
   digitalWrite(STATUSLEDPIN, HIGH);
   digitalWrite(STATUSLEDPIN, LOW);

This section of code is one blink:

digitalWrite(STATUSLEDPIN, LOW);

Now to do that 6 times for 69°, we just do a loop.  This line is the loop:
for (int i=1; i<=TensDigit; i++)   // Blink LED # times for tens digit.  There is also an open and close { } for the code that repeats.

In english this says "Let's repeat some code a few times.  Let's make a counter we will label i, and set it to 1; We will repeat as long as i is less than or equal to the number in the TensDigit variable; and last every time we get to the bottom of the loop let's add 1 to i.

for (int i=1; i<=6; i++){
   print i;  //pretend code to demonstrate

gives us the result of

print i prints the i variable once.  We just call it 6 times, and each time it runs i is different.

Our good friend http://en.wikipedia.org/wiki/For_loop#Traditional_for_loops has some info on loops.

If your new to programming I would suggest going to http://www.codecademy.com/tracks/javascript?jump_to=501c71dfe944b1000201f5e2.  This is to learn Javascript which is similar in Syntax to what Arduino uses.  While you are learning a different language it will teach you to think like a programmer and immediately recognize, hey i want to do a For Loop here or a Do Loop there.
FoamboardRC (author)  traisjames1 year ago
Can I replace the sleepy time with a delay?

Thanks a lot I will see if I can't figure it out.
Delay() would work. SleepyTime is not a built in function but instead one that jrburke99 made (code at http://forum.arduino.cc/index.php?topic=177588.0) which not only does a delay but also powers down much of the chip to save power.
FoamboardRC (author)  traisjames1 year ago
Right. Well thank you for explaining that code I will work on a new code for this soon. Thanks!
FoamboardRC (author)  traisjames1 year ago
Thank you I looked up modulo and I had my dad explain it to me. I understand now how that works. I'm still having trouble coding. I can get the temp split into 10ths and 1nes but I can figure out how to get the the LED to flash several times without still going through a bunch of if statements 1-9.
Edgar1 year ago
Nice! These pulses could power an analogue counter, of sorts... Small disks with Digits on them, like those on old Pinball machines, but lots smaller.
Voted, and Blogged about it:
Edgar1 year ago
Nice! :)
Voted, and also Blogged about it, too useful to pass un-noticed:
What if the temperature was to 100 degrees Fahrenheit?
FoamboardRC (author)  Creeper377571 year ago
You could make both LEDs flash very fast if you wanted to! I just didn't do that because it doesn't get 100 where I live. If it goes below 0 degrees you could have the LEDs flash slowly. Just a few simple if statements.
Or just make the first LED blink 10 times. As long as there's a clear pause between 1st and 2nd LED it should be easy to tell. Ten in a row, it's 100. Ten in a row, pause, 1 and it's 101.
FoamboardRC (author)  maggiemcfee1 year ago
halamka1 year ago
- yintercept -- The most difficult, fundamental digital computer loop is binary division. I figure that a memory string is needed to store the BASIC commands. With a loop of course. ENTER becomes a BASIC entity. FORTRAN computers of the 1970's were actually more sophisticated with numbers. Note that Microsoft computers had 4 original partners.
halamka1 year ago
Scale factor = X , atd / x = int , if int < > then flash . It may be that Bill gates / paul allen is drawing attention away from microprocessors. I just got a large computer monitor. I have 20 mhz z80 chips that can load a single screen in 480x240/20,000,000 = .006 seconds from memory. The Commodore 64 computer could always instantly fill the screen from memory.
halamka1 year ago
I have been ignoring arduino because it seems to fall into a category of microsoft nonsense. What is the 8 pin chip? Is it secret so asian factiory workers can go home?
FoamboardRC (author)  halamka1 year ago
Hi. If you did this project with Dallas DS18b20 temperature sensor - it could power just a CR2032 tablet battery (3 Volt) and will be small. Attiny 45/85 exellent work with 3 Volt. Flash of tiny 85 will be enough for program on IDE Arduino with all needed lib
FoamboardRC (author)  elektrikpco1 year ago
True. I had a LM35 and wanted to use it. A 9v battery is also more convenient.
manuka1 year ago
Much the same approach, but with simpler code, can be done using a high level PICAXE-08M. On the compact Celsius scale I used longer flashes for tens, & shorter for units. Hence 24 Celsius = 2 longs then 4 shorts. Sub zero could also be organised, but it rarely gets that cold here (Wellington, New Zealand)!  For the sensor a DS18B20 is preferred, but even a cheap thermistor may do. Refer details =>http://www.picaxe.orcon.net.nz/NTC_thermo-Swan-code.pdf
FoamboardRC (author)  manuka1 year ago
Hey thanks for the suggestion but I am trying to stick with Arduino and it's language.
That's a really good idea! Long, then short.
dmoore751 year ago
Could you use a for/next block to scan through temperature ranges instead of using case statements? No experience with AT Tiny, but it's supported in Arduino IDE. This should help to reduce your code size and give more accurate readings.
FoamboardRC (author)  dmoore751 year ago
I'm not sure what you mean by more accurate because it doesn't matter how I go through the temperatures it's gonna be the same whether I use if statements, cases or whatever. I don't know how to use a for/next block. If you'd like to to make a new sketch I that would be awesome! Yeah, that would reduce the code size and be easier. Like I said in the beginning, I didn't really know how to do this. The code I made was made from a beginner.
carlos66ba1 year ago
Nice/ You could use 3 AAA batteries (does not take much more space than a 9V) and skip the voltage regulator.
FoamboardRC (author)  carlos66ba1 year ago
Yup I just don't have that :D
jrburke991 year ago
Here is a post I made on the Arduino forums with all of the details and my code, etc. Hope this helps you out!

FoamboardRC (author)  jrburke991 year ago
Thanks I have checked it and am trying to figure some things out.
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