IR Wireless Temperature Sensor With ATtiny85




About: I'm student in The University of Sofia (St. Kliment Ohridski) in Bulgaria. I have a lot of interests, most of them are related with electronics,pc and programming.

Arduino is simple and very powerfull open source/hardware platform where only your imagination can stop you.A few days ago I read an instructable that inspire me to do my own.The instructable is about how you can send strings of data from one arduino to another.Everything is ok but I wanted to make it with Attiny85 .but unfortunately libraries are not supported with this microcontroller.So, I need to find a way how to generate 38khz and send modulated data and how to translate those data.I'm not enough pro :) to know how attiny85 to generate 38khz itself so I used old good one 555 timer.Everything is good but now I must to send data somehow.There are 3 possibilities:

1-By controling reset pin of the 555 timer

2-switching on/off power supply of 555 timer

3-switching on/off LEDs(timer is always on)

I used 3th variant.

Let's start!

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Step 1: Parts List

Microcontrollers and timers:

1x555 timer

1xATtiny85(you can use any microntroller from Attiny family)

Resistors and trimers/pots:




1x10k trimer/pot






Any pnp/npn transistors.In this project I used 1xBC547(npn) and 1xBC327(pnp)


LM35DZ couse it's easy to use



LEDs and transmitters:

Any IR leds.

You can use any ir receiver.Why??Because you can tune to the right frequence 555 timer with 10k trim/pot.


*To be exactly 38khz you must to tune trimer/pot around 7.979k or just mesure frequency with multimeter

*Supply voltage can be everything between 6.8v-30v
*Attiny85 is running at 16mhz internal oscillator

Step 2: Shematic and Pinouts

Step 3: Transmitter Code

After you finished with circuit you must to upload some code..right? :D

In my project I used morse alphabet to send data.

There are two files, first one is little modified Morse library and the second file is main program.
I uploaded the code trought Arduino with tiny cores.
You can find it here:

Step 4: Receiver Code

It can be done a lot of optimizations.Because now you can only send numbers(in my case temperature).

Step 5: Update

Couple pictures how I integrated this circuit.

Step 6: Final Product

Basic characteristics:

Next goals:

Single chip solution, less power consuption
Please comment and share your ideas for improving this device.
Thanks for reading!

btw: English is not my native language so sorry for mistakes and etc.

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    5 Discussions

    dude, in order to send 38khz with attiny85, you have to use an 8mhz crystal and you can control the IR leds using the PWM pins... there is some kind of math involved to divide the clock impulses but you're gonna make something nice.


    5 years ago

    What is the function of the attiny in this circuit?

    3 replies

    Reply 5 years ago on Introduction

    Attiny read the temperature from lm35dz ,convert it to morse code and then send it to IR LEDs.


    Reply 5 years ago

    Why not just send the data directly over IR?


    Reply 5 years ago on Introduction

    Because you need to generate 38khz and I don't know how to do it only with attiny85 without additional ICs.So to do the task I'm using 555 timer.