This post looks at six slightly more esoteric ways of sensing the environment.
So many projects use commonly available sensors to detect heat and light levels along with pressure and movement etc. However, these represent only the tip of the iceberg and there are many more ways of sensing the environment and that range from useful, through unnerving to surprising.
TCS3471 development board
Sensors that can be used to determine the colour temperature of light have applications in everything from photography and desktop publishing, to fish keeping and astronomy.
The TCS3471 from AMS is a tiny colour light-to-digital converter with red, green, blue and clear channels, that interfaces with a microprocessor via I2C. Tautic Electronics have produced a development board for the sensor and Raivis Rengelis has created an Arduino library,
Lightning detector schematic (image source: techlib.com)
Back in November I wrote about the novel AS3935 lightning sensor IC from AMS and how it could easily be put to use with an Arduino thanks to, once again, a development board from Tautic Electronics and an Arduino library from Raivis Rengelis.
At their most basic lightning detectors are simply receivers that pick up the RF pulses generated by strikes, and if you enjoy building circuits from first principles a great place to start is Charles Wenzel's excellent Techlib site. Simpler circuits may not always be able to distinguish strikes from man-made interference or have as many features as the AMS chip, but are fun to construct and use.
HSN-1000 Nuclear Event Detector (source: maxwell.com)
The nuclear event detectors from Maxwell Technologies are triggered by the ionization radiation that is generated by the detonation of an atomic weapon, and drive a normally high pin low within 20ms of such an event being detected.
This is one detector you never want to see triggered!
MightyOhm Geiger Counter Kit (CC BY-SA 2.0)
Far more interesting to use than a nuclear event detector — and with somewhat less sinister overtones — is a general purpose radiation detector. These are frequently referred to as Geiger counters, although a Geiger-Muller (GM) tube is just one way of detecting ionising radiation. Other methods include the scintillation counter, where radiation strike causes a material to emit light which is then detected, and the incredibly simple ionisation chamber.
In May of last year I first wrote about an ionisation chamber detector that I was prototyping for the OpenRelief project, and where the active element is little more than an old treacle tin plus a length of wire. Once again there is a great selection of simple to construct circuits on Techlib.
There are also plenty of Geiger counter circuits available online and surplus GM tubes can be picked up quite cheaply on eBay. With complete kits such as MightyOhm's providing a quicker route to building your own Geiger counter.
A prototype Muon detector built using fluorescent tubes (source: hardhack.org.au)
OK, so this is just a particular class of ionising radiation, but what could be more fun than detecting very high-energy particles originating from outside the Solar System! Cosmic ray detectors feature in the news from time to time, but these ones tend to cost upwards of millions of pounds and to be buried deep inside mountains so as to shield them from unwanted sources of radiation.
Robert Hart's website provides a fantastic resource for intrepid experimenters with a modest budget, where he describes detectors he's built using classical approaches based around scintillation counters and GM tubes, alongside novel hacks using pin photodiodes and even fluorescent tubes!
The earth's magnetic field
Plot of the earth's magnetic field during a geomagnetic storm (source: Geller Labs)
Measuring the earth's magnetic field can be much more interesting than it may at first sound... The strength of the field varies on time scales from milliseconds to millions of years, and more severe variations known as geomagnetic storms can result from massive bursts of solar winds which are capable of damaging satellites, and causing aurora and power outages.
It is possible to measure variations in the earth's magnetic field with some of the more sensitive magnetometer a.k.a. “digital compass” ICs. However, in order to get any real sensitivity you need to use an instrument such as a proton precession magnetometer (PPM).
The PPM might sound like a highly complex piece of equipment, but the principle is quite simple and involves using a strong magnetic field to align the protons in a fluid that contains lots of hydrogen atoms, then interrupting the field and measuring the very weak field produced as they realign themselves with the earth's magnetic field.
PPMs can be constructed from PVC tubing containing a liquid such as paraffin, hand-wound wire coils, reasonably simple circuits and a PC with a data acquisition card. There is a Yahoo! Group for those interested in building their own PPM and a Geller Labs supply a low cost kit of parts.
Whether you're an amateur scientist or an Internet of Things (IoT) developer, or simply a electronics engineer or hobbyist interested in novel projects, when it comes to sensors there is an incredibly diverse range of options available, it's surprising what can be achieved with simple circuits and neat hacks, and a great deal of fun is to be had experimenting!
Top image: proton precession magnetometer coils (source: Geller Labs)
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