Me and Ana always exchange "things we've done" for Valentine's, this year I got a knitted cap and a scarf. Since my ability to do anything "pretty" is quite limited, I thought about buying something and modifying it.
I saw a mini-Munny from Kidrobot in a local arts shop (Artifac), and I thought of the possibility of making it a bit more "interactive". The mini-Munny is a small DIY toy (you can paint it anyway you like) and made of transparent Vinyl and is available on various colors. I thought of placing a RGB LED that would sense the environment temperature and would change color accordingly. I though of using a Atmel AVR ATtiny15L driving directly a RGB LED from Sparkfun and using a LM35CZ to read the temperature. The ATtiny15L appeared the best option, I had some in my parts boxes, works from 2.7 Volts up, is programmable in circuit and has a ADC converter, useful when the only temperature sensors I have are analog output.
At this time I decided to use a color code for the temperature, blueish tones to cold temperatures (less than 19C), from 19C to 21C greenish, and from above 21C reddish. I placed 100Ohm resistors in each output to the LED so that programming in circuit was still possible, a better selection of resistors could save power but for now it was just enough. The supply of the temperature sensor is connected directly to an micro output, just turning it on when a measure is in progress, I also placed a RC filter on the output of the temperature. The LM35 was what determined the supply voltage and the number of batteries, its minimum operating voltage is about 4V, so I had to use 3 coin cells (4.5V).
The I built a small circuit board, with a SMD version of the Atmel, the LED, the temperature sensor and the ISP connector. I added a small blob of transparent FIMO to mix the output of the LED.
I was luck, the batteries "just fit" Munny's neck and the circuit also "just fits" the Munny's head.
Finally, the circuit is inserted inside the Munny's head and gives a colorful indication of the temperature every 3 minutes... or about...
Here is cold... blueish...
If you want to see more colors and other pictures, Ana has posted some more photos with other colors.
The original idea was an electronic Valentine's card... but I could not find any suitable carrier for it... you can't just give a breadboard to your Valentine's can you!! It was a ATtiny26L and a Nokia3310 display.