As makers we like to bridge the gap between the analog world and the digital one. Grabbing real-world data, analyzing it, and reacting to it is much more exhilarating when the process takes place through electronics as opposed to, say, our brains. Sure, you could always stick your beak outside and predict a chilly day. But, it’s just so much more satisfying that your custom mobile weather app will also send a signal heat up your coffee a few extra degrees in preparation. This is why we love sensors.
This week we’ve pulled together three tutorials on some interesting sensors to help you collect the data you need, or maybe provide some inspiration for a project.
The technique of pulse oximetry has been in use for a number of years now to quickly establish a pulse measurement in the hospital. The idea is simple: shine two wavelengths of light through some blood vessels and track how much of the two wavelengths bounces back to a light sensor over the course of time. Blood absorbs certain light wavelengths better than others, so when the vessels contract, there is less blood in that area and the light absorption changes. Modern Device makes acquiring a pulse sensor super easy with their Pulse/Heartbeat Sensor board. They cleverly re-purposed a proximity sensor chip, the SI1143, by Silicon Labs to perform the light sensing, but programming it is not so straightforward. Fortunately, Modern Device hosts a series of tutorials written by Paul Badger to help acquaint you to pulse-sensor programming.
Adafruit has a nice tutorial for using their temperature and humidity sensors. These sensors can be used for a number of projects, including gardening, cooking, weather stations, climate control, and more. Most basic temperature sensors are actually heat-variable resistors called thermistors. When the temperature changes, you only need to check the relative change in resistance and do some math. Simple humidity sensors are actually humidity-variable capacitors which are partly made from a moisture-absorbent material that expands when exposed to water in the air. Similarly, you just measure its capacitance. Neat, right?
Piezoelectricity, discovered by Jacques and Pierre Curie, is electrical charge caused by pressure in certain materials. The phenomenon is reversible: electrical fields applied to certain materials create internal pressure. One common application of this is piezoelectric speakers and microphones. Sound waves apply pressure to a piezoelectric material which generates an electric signal which can be interpreted as audio. Likewise, an electric signal through that same material causes internal pressure which can be translated to vibration. Piezoelectrics are rather cheap pieces of electronics, though: you can get a sound from them that would make an audiophile cry. On the other hand, you can pick up a decent piezoelectric microphone. Most people in the Maker community should be familiar with the piezoelectric buzzer pictured on the right. As described in a forum post here, you can set this up as a reliable knock sensor. Maybe make a knock-based lock for your door!