This page covers sensors
and related implements,
Sensors and Related Modules and Components:
I continue to find pertinent information on sensors the home constructor might build and use. This file is intended for those who may wish to 'roll their own', and is organized by 'function' or the specific environmental parameters you may wish to monitor, and some of the components you might use to get it done. This file does not pretend to be thorough or all-inclusive in its coverage. It is based on my search for components and designs, and is biased by what I consider to be some of the simplest and most useful approaches to monitoring, to a reasonable degree of accuracy.
There are many other available components and instruments by a wide variety of manufacturers, and you can locate these with web and other searches, as I have done. This file does not offer you a complete design for a 'weather station'.
In developing a monitoring function or weather station, you might consider using one of the earlier vintage of microcomputers as a controller and display driver. Computers such as the VIC-20, the Commodore 64 or 128, the Rockwell Aim 65 (6502 processors), the Radio Shack Colour Computer (6809 processor), and even the little MC 10 (6805 ?) or the ZX81 (Z80A cpu) are still to be seen at electronics and ham radio flea markets, usually at give-away prices. Do you have an old PC based on the 8086, 80286, etc, ? These computers can all be programmed in Basic, Forth, assembler and other languages, and any one of them could serve as the basis for a monitoring station. Some people even have a modest collection of these old computers (Who, Me ?).
Microchip Technologies Inc. Your source for PIC processors, the least expensive (hardware cost) approach for controllers. There are a wide variety of PICs available. To use these as the basis for your design, you have to be able to write the program in assembler, and 'burn' (program) the controller. There are designs available for inexpensive programmers. Search recent issues of QST magazine. There are many useful and interesting application notes on the Microchip web site, in addition to information on their many PIC micros.
Parallax Inc. Manufacturer of the Basic Stamps I and II controllers. Lots of potential here for relatively easy programming in a variety of 'Basic'. Great if, like me, you are not a software guru. Specifications and all documentation are available on the Parallax web site, including programming manuals and a wide variety of application notes. Parallax manuals are available for downloading from the Parallax web site for environmental monitoring applications, industrial control, and other areas of interest.
Parallax has a new controller, the Basic Stamp II Plus, a super-stamp that has a variety of features including new commands to support the Dallas Semiconductor 1-Wire protocol. It is available in 24pin and 40pin versions (more I/O). The 24pin unit has 16 I/O pins, and the 40pin unit has 32 I/O pins. The BSII+ commands are defined in the Basic Stamp Manual Version 2.0, which can be downloaded from the Parallax web site. Having support for the 1-Wire protocol as well as 'conventional' Basic commands will obviously facilitate using a wider range of types of sensors and support components in a given monitoring system.
Peter H. Anderson has a kit for the Basic Stamp II controller, if you are willing to wire it up or to use it on a prototyping board (solderless breadboard) . There is no printed circuit board available. The BS II comes out at about half the normal cost if you build it. He also has kits for a simple digital probe, and other very useful kits and components - see further notes on these below under specific sensors. Check his web site for documentation on the application of PIC and Basic Stamp II controllers for environmental monitoring.
BasicX-24 by NetMedia is another microcontroller that has potential for a sensor controller, and other projects. This controller is pin for pin compatible with the Parallax Basic Stamp II and BS IISX. The advertising claims it supports the Dallas 1-Wire system, however, I have not been able to find anything specific on this capability on their web site. It's probably in the programming manual. This processor has floating-point math and co-processing ability, serial I/O, 8 input 10-bit ADCs, room for 8,000 lines of code, etc.
The Wilke Basic Tiger is another controller family that should be excellent for monitoring projects, with multi-tasking, floating point math, etc. Several configurations are available.
A useful Canadian company to know - they will ship to any country - is HVW Technologies. They specialize in robotics kits and parts, and supply Parallax Basic Stamps and accessories including the Basic Stamp II Plus, the OOPIC, PIC processors and other related materiel. They have a new kit for building a Basic Stamp II on a PCB at a reasonable price - it's called the Stamp Stack II kit. It is designed to insert into a prototyping board or for wiring into a project directly. The price is $49.95 C.
Many builders of weather stations or environmental sensors will use a PC for their controller and display. Used earlier-generation computers abound, and are an inexpensive approach for a dedicated system. However, not everyone wants to use a big PC or even a laptop computer for this purpose. Another approach is to use a microcontroller and a liquid crystal display. The LC Display permits placing the data display almost wherever you might want it . You could use an LCD for a portable instrument.
Scott Edwards Electronics - Used to produce 'Counterfeit' Basic Stamp I kits, serial Liquid Crystal Displays, an 8880 DTMF transceiver kit (you can send data by wire or radio using DTMF encoding) and other very useful bits. SE Electronics appears recently to be concentrating on serial liquid crystal displays. The serial Liquid Crystal Displays can be used for stand-alone controller-display units, and have the advantage of needing only one output line from the controller, plus +5 volts and ground. 2X16, 4X20 and a variety of other displays are available.
Another 'display' that should be considered is periodic output to a printer. You could use a personal computer monitor or an LC Display for current information, and dump current, periodic and/or average readings to a printer every hour, four hours, or as often as you need to record the information. This would be a good application for the dot-matrix printer you could not bear to throw out, or a small thermal printer like those that were common some years ago, such as the Radio Shack TP-10 which was sold for use with the MC-10 computer. More on this later.
Transmission of Commands and Data
Abacom Technologies markets micro-power transmitters and receivers for data transmission, including on 433.92 MHz within the 440 MHz amateur band (don't use this frequency unless you are a licenced radio amateur). This type of equipment might be ideal for a wireless link between your sensors and your display unit or PC.
Technologies have transmitter and receiver modules for a number of
frequency bands. Some members of the West Carleton Amateur Radio Club
are experimenting with Linx modules for the 902-928 MHz band. For more
information on this activity, see the 'WCARC
902-928 MHz Band Project' web site.
Also, keep checking on the 'TinyTrak' encoder. This neat and inexpensive implement is designed to put Global Positioning System location information out on the APRS network for vehicle tracking. The creator (small 'c') plans to revise it eventually for reporting data from weather stations.
Using DTMF for Sending Command Signals and Receiving Data -
The Mitel (and others) 8880 DTMF transceiver IC interfaces readily to a microcontroller such as the Basic Stamp. See the link above to Parallax Inc. for a kit for the 8880 transceiver.
If you can find it, have a look at the article in May 1998 QST magazine by John Hansen, W2FS, titled 'An Inexpensive, Remote-Base Station Controller Using the Basic Stamp'. This discusses control and monitoring of an amateur radio transceiver with a remote 2 Meter handitalkie. The circuit board for this project holds a Basic Stamp II module, a CM 8880 DTMF encoder/decoder, a 555 timer and two transistor switches. This board is adaptable to many projects including environmental monitoring and data transmission - with considerable modifications to his software, of course.
Circuit boards for this controller are available from Far Circuits. FC can, I believe, supply a copy of the QST article.
Notes on Sensors and Components
A variety of instruments are based on the position or the rotation of a magnet, often sensed by the closure of a reed switch. Rare-earth magnets in a range of shapes and sizes from 1/8 to 1 inch diameters are marketed in Canada by Lee Valley Tools Ltd. You can make purchases online. These magnets are very powerful for their size. If you get two of the larger magnets stuck together, you will have trouble getting them apart.
Analog to Digital Converters - ADCs
There are, of course, a large variety of ADCs available from many manufacturers. One which is reasonably priced, conveniently available and well documented for applications such as for weather sensors which output an analog voltage, is the Linear Technology LTC1298.
The LTC1298 is a 12-bit ( 1.22 millivolt resolution referenced to a 5 volt supply) sample-and-hold ADC (helpful with values that may change while the conversion is being made). It requires little current, and can do up to about 11,000 samples per second. It can be configured as a two-channel ADC or as a single differential ADC. The operating temperature is from 0 to 70 degrees C. All of this in a little 8-pin dip IC. The LTC1298 is available from P.H. Anderson.
Considerable information on the application of the LTC1298, including data from Linear Technology, is contained in the file LTC1298_12-bitAtoD_Converter.pdf, available for downloading from the Parallax web site. This is an Adobe Acrobat file. P.H. Anderson also offers documentation on using the LTC1298 with the Basic Stamp II controller.
- Wind Speed and
This site - Anemometers - by R.T. Smith of the University of Michigan has descriptions of all of these types of anemometers, and links to articles on building anemometers - mostly of the rotating cup variety. This is an interesting site with lots of background information and links.
Peter Anderson has an add-on kit to his PIC-based weather station that will detect wind speed and gust, based on sensors such as the anemometer (kit) from Fascinating Electronics or one that you might build using similar principles - counting rotations of the anemometer based on closure of a switch (a reed switch closed by a magnet on each rotation).
Do it yourself Anemometer - Detailed information on how to build your own anemometer. The control/display unit requires a programmed PIC and indicates wind speed and direction. The software approach to getting 'direction' is novel and interesting. ( I would not use it, but it is novel).
Generally, these sensors are based on a vane which
turns with the wind and either
A kit for a potentiometer-based wind direction indicator is marketed by Fascinating Electronics . They also sell the potentiometer separately, including a weather-sealed model, for those who want to build their own instrument. The wind direction (value of the potentiometer) can be read with an analog to digital converter (ADC) such as the Linear Technology LTC1298.
Temperature - sensors for inside and
outside air, soil, water, machinery, etc.
More to follow.
The Motorola MPX4115AP is a convenient sensor to interface with the LTC1298 ADC. It runs on 5VDC and outputs a linear voltage which varies with atmospheric pressure. The sensor is functional from -40 degrees C to 85 degrees C (-40 to +185 F). The A suffix refers to an 'absolute pressure' sensor, and the P (or S) suffix refers to 'ported' which is what you want (the AS version is similar but with a different type port). The port (a small spout on the IC) allows the attachment of suitable tubing to reach to the great outdoors. The small plastic tubing you can buy in an aquarium shop will be OK. If you port the sensor inside a building, the pressure will likely fluctuate when doors open or close, or when the elevator goes up and down, or when the furnace or air conditioner fan is operating.
The MPX4115AP was not stocked in Canada when I checked, but can be ordered from distributors in lots of twenty or so. If you don't need that many, check with P.H. Anderson. Professor Anderson's add-on kit ( for his PIC-based weather station) for barometric pressure employs a Motorola MPX4115AP or AS sensor and is $29 US. This kit includes a dual sample and hold A/D converter IC (LTC1298) suitable for interfacing the pressure sensor (plus an additional sensor such as for relative humidity) to a PIC or Basic Stamp II controller. You can purchase the MPX4115AP without the A/D converter IC for $20 US.
Note that the MPX4115AP should be provided with 5VDC directly, as it needs more current than you want to draw from the Basic Stamp II regulator.
Here's a neat and simple design for a 'Digital' Barometer by Radek, OK2XDX, using a Motorola MPX4115A pressure sensor. The output is to a digital multimeter (voltmeter) These DMMs are inexpensive at Canadian Tire Corporation in Canada. The 'digital' part of this design is the voltmeter / display. The output can be set to read directly on the multimeter as kiloPascals.
The Honeywell HIH3610-001 sensor interfaces like the Motorola MPX4115 does for atmospheric pressure and with the same useful temperature range, from -40 degrees C to 85 degrees C (-40 to +185 F), with a linear voltage output to an ADC (such as the LTC1298) proportional to relative humidity from 0 to 100%. For a couple of dollars more, the -003 version of the HIH3610 each come calibrated with a printout. This is useful for more accurate applications, and also means that the specific sensor has been tested. You can find the full specifications for the HIH3610 through www.honeywell.com/sensing.
Some other relative humidity sensors such as the one supplied by Fascinating Electronics function as a capacitor whose value changes with relative humidity. These may be functional down to only about 0oC.
The Honeywell sensors are marketed in Canada through Electro Sonic Inc.
If you need to know if the sky is clear or cloudy at night, you might be interested in the detectors designed by Chuck Koller, N3BEZ, who has an astronomical observatory. These designs use the Heimann Optoelectronics TPS 534 thermopile/thermistor reference. There is other interesting information on his web site on the control and automation of his telescope.
Lightning Strikes - direction and distance
Have you considered looking for
lightning activity electronically, to know where it's coming from and how far away it is
? Do you often worry about lightning coming close to home and frying your computer,
radios and other equipment ?
Here is a design for a lightning detector using the Dallas Semiconductor 1-Wire technology at <http://www.timbitson.com/weather/owlm/index.html>. This could be adapted for a different counting method using your station controller.
Another design for a lightning detector at <http://www.techlib.com/electronics/lightning.html> uses the static crash at radio frequencies of about 300 KHz.
The two designs noted above are intended to count the occurrences of lightning flashes. They do not indicate the distance or location of the storm. Needless to say, you must use lots of caution and common sense in putting probes up for lightning detection. Do so at your own risk. If you do not understand the potential dangers, it would be best to consider buying a commercially-made unit.
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Graham Ide VE3BYT