Sunday, August 30, 2009

Sensor Arrays, Ctd.

Humidity sensors are typically more expensive than temperature sensors and are more complex to design/build a circuit around. As the price goes up, the fewer additional parts are needed but once the price gets beyond the $50 range, I'm not that interested. For about fifteen dollars and about five more in additional parts, a decent humidity sensor can be built. I plan to do some mapping in my home but I am guessing that there are probably not pockets of high or low humidity in my house and having 2-3 max humidity sensors will be plenty.

A few weeks ago I was reading and article in MAKE magazine about a guys who wanted to lower his clothes dryer electricity bill so he sought to use hot air from outside or the attic. I thought it would be a cool idea if you lived in a place with dry heat but don't think it would be feasible here in Florida. At some point I might try it just to see if really hot humid air could successfully contribute to lowering drying time. I think the key is to find a way to take the water out of the air quickly.

Any ideas?

Sensor Arrays

For my home automation project I am designing some sensor arrays to collect various type of data. Examples of sensor types include temperature, humidity, light intensity, proximity, sound and possibly a RFID reader. Each sensor array will be connected to an XBee Series 2 transceiver in order to be linked to the wireless network. When possible, a sensor will be designed to use an energy harvester which will allow the sensor array to run for long periods of time between charges.

An example of a typical array will be one with a temperature and light intensity sensor included in the circuit. Placing temp/light sensor arrays throughout the house will allow me to track hot and cold spots and help determine the best way to keep the house cool while using the least amount of energy. Living in Florida, it is rare to be concerned about it being too cold in the house or how to keep the house warm enough to fight off frostbite.

Typically in my house the master bedroom stays about 3-5 degrees cooler than the rest of the house. This is perfect at night as my wife likes to sleep in a cooler room. However once we are up in the morning and either at work or working at home, very little time is spent in the master bedroom or bath. If the cold air being delivered to the bedroom could be channeled to the living room or the office, it would keep the part of the house being utilized cooler without lowering the thermostat.

Using the light intensity sensors will help map out the brightness of the rooms being used at particular times of the day and determine which areas need additional light as it gets later in the day. What I hope to accomplish is to inexpensively add light to the kitchen/dining room by building lights using 20 Watt LEDs that would dim/brighten based on the amount of light needed. A 20 Watt LED has approximately 1000 lumens, which in incandescent wattage amounts is approximately 100+ Watts. A couple of LEDs could keep a high ceiling, open area nice and bright throughout the day and night.

Energy Harvesters

Energy Harvesters are starting to be mentioned and talked about by some of the technical e-zines. Basically energy harvesters consist of a circuit to keep a battery or super capacitor charged by collecting small amounts of energy using a transducer. Typically the energy harvester is charging a sensor (i.e. temperature, humidity, light, proximity). Transducers can be photovoltaic cells but since many of the sensors are indoors the solar cell needs to be very sensitive. Another option that might be usable is a piezoelectric sound transducer, which converts vibrations to electricity.

The problem I have with all of the examples I've seen is that they are cost prohibitive for what they are trying to accomplish and to the people who would take them and experiment with them. $35.00 for a semi-working energy harvester and over a hundred for an evaluation kit defeats the purpose of getting the technology out there and working with it.

I am in the process of building a small energy harvester using a piezo-electric transducer to power a wireless temperature sensor. I still have a few more parts to procure and some calculations to work out but, if successful, the time between backup charges of the super capacitor could be significantly extended. The most expensive portion of my project has been the shipping charges because I have been impatient in waiting for the parts. The DC-DC Step-Up Voltage Regulator was a little over five dollars in quantities of one and the rest of the parts are off the shelf capacitors, resistors and some low reverse leakage diodes.

Once I have all the parts, assemble them and test it out I will publish the results (good or bad). Energy harvesters have the potential to allow low current applications to run months, years or effectively forever without the need for battery replacement.

More on this subject.

Speed Blogging

While waiting for parts, tools, time to spend and getting my brain working to finish the projects I'm working on before blogging about them I'm going to do some speed blogging where I talk about the projects and some other topics on my mind. Most of the topics will be related to microcontrollers, XBee radios and Home Automation but occasionally I will veer off the path with a rant or two.

Any feedback is welcome. I know you're out there reading so drop a comment or two to let me know you're alive.

Saturday, August 8, 2009

Topic Requests

The blog will start picking up with both short and longer posts on a variety of subjects along the lines of home automation, alternative energy, smart homes and how to design and build items where the costs are not prohibitive.

If you have any ideas and/or requests that you would like for me to write about, feel free to let me know in the comment section or my email address in my profile.