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Nursery Room Temperature Monitor

Let me start by saying I found out a few weeks ago that I'm going to be a father. This is my first child and as you can imagine I'm filled with excitement and nervous energy. Both my wife and I both agreed that we wouldn't start actual preparations for the coming baby until the 12th week to ensure all was well (1 in 4 pregnancies end in miscarriage). I just couldn't sit still and wait, I started reading about what to expect, how to care for a newborn, and so forth.

It was while I was reading about SIDS (sudden infant death syndrome) that I saw a few articles discussing the proper temperature for a nursery to help prevent the SIDS. The articles all agreed that cooler was better, ideally between 64 and 74 degrees Fahrenheit.

I was immediately struck by the idea of creating a visual indicator to allow both my wife and I to easily ensure the room was within this range! I grabbed up my Maker's Notebook and starting drawing what I was envisioning. What did it look like, you ask? Keep reading, you'll soon be rewarded with the answers you seek!

My idea was to utilize a diffused RGB LED, an analog temperature sensor (really wanted to expand my working knowledge of the ADC on AVRs) and a frosted glass sphere to create a highly visible temperature indicator. I quickly sorted through my parts bins and found most of what I would need. A quick search on eBay and a short drive to Lowe's provided the rest.

Here's what you'll need to build one yourself:
1. Wooden base, use your imagination.
2. Frosted glass light shade.
3. LM335 Analog Temp Sensor
4. Atmel ATTiny45/85 micro and appropriate socket.
5. Common anode RGB LED (doesn't have to be diffused, you can do that yourself with sandpaper).
6. Two (82 ohm) , one (150 ohm), one (10k ohm) and one (2.2k) 1/4 watt resistors.
7. A 10k potentiometer.
8. One (.1uF) capacitor.
9. A power source. I used an old Netgear router power supply. 5V regulated output at 2.0A.
10. Some wire, heat shrink tubing, Velcro and appropriate soldering equipment.
11. Firmware and schematic.

I typically breadboard all my designs then move them to PCBs once I've worked out all the kinks, but I had recently purchased a mini drill-press and PCB development kit from Jameco and decided the simplicity of this design would allow me to go directly to a DIY PCB (it also gave me an excuse to try my newHad to calibrate the temp sensor using the 10k pot and my Fluke with attached thermocouple.

Once done, I sat down and wrote up the firmware using AVR Studio 4. After a few more hours, I was all set to try it out. And TADAAA! A fully functioning accurate temperature indicator for the new nursery. I'll paint the wooden base once we decide on colors for the nursery!

A few equations that made my life easier and an excellent article to extend your understanding of the ADC in any AVR:
AVR Freaks (ADC For Newbies)
Convert Kelvin to Fahrenheit