Summer Project

Posted in apartment by antisociology on July 10, 2010

For those just tuning in, I moved apartments in May. While my new place doesn’t have as much character as my old one, it does have the benefit of receiving an enormous amount of natural light. This has allowed me to start growing some plants.

Being a geeky sort, though, I couldn’t leave well enough alone and decided to build a plant monitoring system as a way to learn some electronics. What I envision is a sensor package for each plant that measures temperature, light, and soil moisture. All of the sensor packs would plug into a central data display/logger unit. This main unit would allow you to look at the current readings, possibly scroll through previous readings, or transfer readings to a computer.

I ordered some Arduino starter stuff from SparkFun and have been messing around. Arduino is a small microcontroller board that makes it easy to get started with some embedded programming. A microcontroller is like a very very very small computer (in terms of size and power) that generally runs only one program, unlike your desktop or laptop that runs many programs. Microcontrollers are responsible for things like controlling your microwave, managing a car engine, or running an iPod.

Arduino board with light and temperature sensor prototype

The arduino board (bottom) and prototype sensors (top)

A few nights ago I started wiring up temperature and light sensors. It took a little doing, but I was eventually able to convert the raw readings from the temperature sensor into human units. I’m still working on figuring out how to convert the light sensor. For kicks, I let the sensor run yesterday while I was at the office. Apparently, my apartment warms up to 90F during the day!

The interesting thing to me is that you can clearly see two main events. The first is when I turn the A/C off and leave for the office. Almost immediately, the temperature begins to rise. The second event is when the A/C automatically kicks on (I set the timer to turn on the unit about an hour before I expect to get home).

It’s also possible to see how the “energy saver” mode of my A/C unit works. I have the thermostat on the A/C set to 77F and have turned on the energy saver mode. In the plot below, you can see how the unit maintains the temperature for a while and then shuts off. The temp slowly rises again, and then the air conditioner turns on again to lower the temp.

I wired up the light sensor too and can’t wait to see how light levels change throughout the day. It will also be interesting to see how interior temps fare once I get shades. Hopefully that will bring the peak temperature down and the A/C won’t have to run as long/hard to keep the apartment cool.

Sensor package prototype

The next step will be to design and build some soil moisture sensors and then figure out how to package the sensors up into a vaguely neat and attractive package.

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