Microcontrollers

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.

Data Displays

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.

For serial LC Displays, you might also check out Crystalfontz and Netmedia Inc.

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.

Linx 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.

If you intend to put your weather station information on the amateur radio APRS (automatic position reporting system) network the PIC Encoder project at TAPR seems like a way to do it.  This stand-alone unit replaces a separate Terminal Node Controller and will form the UI packets for APRS and control your transmitter to put the information on the amateur radio APRS network (with some software work on your part).

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 -
Perhaps developing digital protocols is your area of interest.  If it is not, and you have a system where the monitoring part is remote from the display and recording part,  you can benefit from the fact that most personal monitoring systems do not need to have data batted back and forth in digital packets at high speed.  It is worthwhile to consider communicating over the telephone system, other wires, or low power FM transmitters and receivers and using DTMF tones (dual tone, multi-frequency, such as are used for telephone dialing) for sending commands and receiving data at modest speed.  'Modest' means 'slow' in computer terms, but are you really in a hurry?.  With a controller and 8880 DTMF transceiver at each end of your system and using two DTMF digits for each character, you can send or interpret characters in the basic ASCII table including numeric, alphabetic and control characters.  Check out this Table of Characters for encoding information using DTMF signaling.

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

Magnets

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.

Anemometers - Wind Speed and Gust

Anemometers have been designed that are based on at least five basic physical attributes:

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
- rotates a dual-wiper potentiometer (which therefore has no dead zone) and outputs a voltage to be read with an ADC, or
- rotates a three or four bit encoder disk, usually with infrared LEDs and phototransistors to read the position of the disk and output a binary value, or
- orients a magnet over reed switches laid out in a pattern conforming to North, Northeast, East, Southeast, etc. The reed switches and the following circuitry indicate to the controller in which compass direction the vane is pointing at the moment of sampling.   More to follow on several approaches you might employ to read the reed switches.   If you want to be all solid state, Hall Effect devices could be used instead of reed switches  to detect the wind direction with the magnet.  However, reed switches are very reliable and long-life devices, and may be less expensive and easier to obtain than the Hall Effect devices.

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 DS1620 three-wire smart sensor
Project X - 8  temps with DS1820s
P.H. Anderson's PIC-based temperature sensor kits for DS1820s OR 1821s

Atmospheric Pressure

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.  

Relative Humidity

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 0^oC.

The Honeywell sensors are marketed in Canada through Electro Sonic Inc.

Rainfall - 
Tipping Bucket rain gauges.  These measure rainfall by collecting water in a small bucket that tips at a certain point, and when it tips a magnet passes by and closes a reed switch, and a counter records this action.  The rain gauge is usually calibrated to the number of 'tips' counted that in turn indicate how many  inches of rain have fallen.
The rain gauge kit marketed by Dallas Semiconductor for use with the 1-Wire system could be adapted for counting with your system controller.  See Peter Anderson's web site for a PIC-based counter that could be used for the Dallas unit or a home-built rain gauge.

Water flow - If you want to measure water flow in a stream or river, this could be a counting operation using a propellor or paddlewheel driving a magnet rotating over a reed switch, similar to the approach used for the rain gauge or anemometer.  Placement and calibration of the instrument could be interesting.

Ambient Light - More to follow.

Sky Conditions - sky temperature/cloud cover

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 ?

There are several approaches to plotting the location of lightning strikes that are used by the government services networks in Canada, the USA and elsewhere, such as the time of arrival of energy from an individual strike at each of three or more monitoring stations, and computing the location from this information.  The monitoring stations use timing from the Global Positioning Satellites and send the data by satellite to a central unit for processing.  The computed location information is then relayed to weather offices, all in a matter of moments.  You can learn about these approaches by searching the WWW for 'lightning detection'. 

As an individual, you probably don't need to know the location of each individual lightning strike.   However, knowing generally where the lightning activity is from your location and how far away it is would be both useful and interesting.  You could estimate if the electrical storm is going to make it to your location.  I remember that many years ago there was an article in QST magazine for a detector design that did this, showing on an oscilloscope the azimuth and approximate distance of lightning activity .  This design used two loop antennas oriented north-south and east-west.  I searched the web for a design for a similar lightning monitor, and I finally found one that could be readily built by an individual.

Pennsylvania State University hosts a design on the Web for the GP 1 Lightning Locator.  It is intended as a stand-alone detector of lightning cells and can plot their locations out to about 500 kM from the receiver.  The display is to a map overlay on a PC monitor.   This detector uses crossed loop antennas, and could be built by anyone sufficiently interested.  The web site has complete design details for the antennas, circuits for the electronics, layouts for the printed circuit boards, and downloads for the software.   You will probably find this design interesting, even if you do not plan to build a system yourself.  Building a GP 1 station could be a worthwhile group or club project.

A commercial design using the same principles as the GP 1 is sold by Boltek, the LD250 interfaced to a laptop or desktop PC, for $799.00US.

   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.