>>>READER-TO-READER QUESTIONS AND ANSWERS
conditioning compressor off when going uphill to save energy, but turn it on when going downhill as the engine is idling
and the energy to drive the air-conditioner is essentially free.
GPS units are fairly accurate at computing altitude. Are
directional accelerometers or GPS units sufficiently quick
and accurate to produce such a signal? I have also seen
digital levels that must produce an off level signal to send to
a readout or display. How might these devices be used?
#1 The two most common ways of determing elevation
and changes in elevation are GPS and barometric pressure.
I'm not sure what kind of hills you are dealing with, but
where I live, there is no problem determining whether the
vehicle is going uphill or downhill as the hills are STEEP! So
I have to assume you are concerned about topography
which is not as severe as what I have to deal with.
For the past year, I've been using a Vetta V100a bicycle
computer on my bicycle. It not only displays present
elevation but also indicates grade and whether the elevation
is increasing or decreasing. It senses barometric pressure
to do this.
If you are looking for something with an audible output,
look around for what is called a Variometer. However,
unless you like looking at rotating inductors, I suggest you
type paraglider, ultralight, aircraft, or barometric pressure
along with variometer when using an Internet search engine
such as Google.
If you want the ultimate change of elevation indicating
device which will read out the ELEVATION TO A THIRD OF
AN INCH, you might want to check out the UP24 - High
Resolution Air Pressure / Elevation Sensor Kit sold
by Ramsey Electronics;
K3PGP - John
#2 What you are describing is more along the lines of an
"inclinometer." They are often used in off-roading vehicles,
so you can find a supply of them at any nearby off-roading
store. As well, you can check eBay or similar for low-cost
If you wish to do this yourself, there are still other
options. You can purchase inclinometer sensors directly.
The absolute cheapest will be found at a hardware store. It
is designed to be used to measure the angle of any surface,
and is essentially a stiff piece of plastic with a weight on the
end that is free to rotate. It will always point down, so by
fixing a scale behind it relative to the surface, you know the
angle. This won't work if you are accelerating or bumping
around in the car though, as it will throw the readings off.
To use one of the many MEMS accelerometer devices
you have seen around, check out Freescale's application
note on the subject, AN3107. As well, see the article on a
self-balancing robot, Part 2, which appeared in the
December issue of Nuts & Volts. GPS could potentially
work, but you would need a device that can receive WAAS
signals for an accurate enough fix. Search eBay for "GPS
Mouse"; there are a number of GPS units about the size of
a computer mouse you can get. They are sealed and have a
magnet mount so you can put them on top of your car. Get
one with serial output and you can interface it to a
microcontroller/Stamp device. They all output NMEA data,
if you search the web, you'll find all sorts of example code
for interfacing. Then it's just a matter of seeing if your
altitude is going up or down.
[#1074 - January 2007]
What is the frequency and mode used by the small
outdoor temperature transmitters? Is the data serial? Is there
a standard format?
I have found many of the weather forums say that
several transmitters are on 433.970 MHz. Yes, the data is
serial. There are some "standard" formats, but many do not
follow them. My $60 weather station certainly does not,
according to the discussions. There is a forum I have found
www.weathermatrix.net/. Several of the
weather stations use chips by Dallas Semiconductor/Maxim
and therefore could be called a sort-of standard. Of course,
if you have a simple thermometer, it might not be using the
same chips as the weather stations. If you do a search for
433 weather, you will see many weather-related items pop
up, but I suspect the frequency is between 433 and 434,
not exactly 433.