Part 4 - Sensors
As I stated earlier, my goal is to replicate as much actual tricorder functionality as early 21-st technology will allow, so to me sensors are the heart and soul of the project. If not Klingons behind rocks, what exactly can we sense? Quite a bit, it turns out:
Non-Contact Heat Sensing - A single point, high precision thermopile, or an array of them (an IR camera). These detect blackbody radiation in the far IR (different from an IR flame sensor). I have both in my DST and find them very useful.
Atmosphere/Altitude/Gasses - Ambient temp, humidity, air pressure - the barometer can be used to estimate altitude. Most of the gas sensors are larger and relatively power-hungry, but there's a small VOC sensor that doubles as a breathalyzer - because that Saurian brandy can sneak up on you.
Magnetisim - the 3-axis MEMS units are compact, sensative, and can calculate compass headings. I've also installed a single-axis fluxgate magnetometer, which NASA uses in satellites - real outer space technology there. Bet V'ger had one.
Light - Lots of choices here spanning UV, visible, and IR - single-frequency, RGB or even limited-band spectrometers. I'm evaluating a brand new board from Sparkfun, a 6-band near-IR spectrometer that may be able to discriminate/identify rocks and minerals.
Audio Spectrum - Some small mics range up into the ultrasonic, which meets my goal of detecting things I can't directly observe. You can also tell if your stereo is loud enough to annoy your neighbors.
Radiation - There are geiger tube and solid state detectors that can fit in the case. I've employed a tiny commercial radiation mic that can detect emissions from old watch-hands and a Thoriated camera lens from the 60's, and hopefully some of our native radioactive minerals.
Electromagnetic Fields - Very interesting to see where power fields are in your house (basically everywhere). There are also lightning detector modules - we don't get much lightning here in Burbank, so I've never installed one.
Metals - Short range detection, and limited discrimination (iron reads differently than silver or stainless steel). I never thought about the amount of iron in rocks, or even my own veins, until I added this to my first build.
Capacitive (Dielectric) Sensor - Similar technology to a stud sensor. Can also detect fluid level in an opaque container. While precise measurements are difficult, you can at least characterize the dielectric constant of a material.
Motion - In addition to PIR sensors (think automatic patio lights), there are miniature doppler radar units that can detect motion through walls! Not quite Klingons behind rocks, but getting there.
Distance - there are sensors covering ranges of 0-100cm or 0-100 feet, utilising ultrasound, IR, or lasers. Some of the sensors, however, require large holes to be cut in the case. They all work better indoors than out.
Gyro/Acceleration - I haven't found a real use for these, but they are inexpensive and straightforward to implement.
Location (GPS) - Again, I haven't used these. They used to be quite power-hungry but the latest units have reduced current draw.
Biomedical - Lots of options, and I'll put as many as I can in my next build.
Non-sensory components - extra EEPROM (Memory Banks in TOS lingo), SD card readers, Real-Time Clocks (neither Arduino nor Pi have an RTC built-in), digitally-controlled LEDs, etc.
The beauty here is that we have such a wide selection of capabilities to choose from, and you can tailor your sensor compliment to your intended use. Many of these are tiny MEMS (Microelectromechanical systems) sensors, the same type found in your smartphone. Others are simple analog sensors that output a voltage proportional to what they're measuring. We'll talk about how they connect to the Arduino when we get to the build.
Starting to feel like we've got a foot in the door of the 23rd, right?