Hi
i'm currently looking for solution to monitor external environment from
an openbsd server.
I'm currently trying to play such game... yes playing... not working...
:-)
has anyone advise to find cheap sensors (temperature, but also humdity,
pressure, light, electricity before UPS, ...) which are known to work
with openbsd ?
After a long time of lurking and looking through solutions like USB,
Ethernet, serial busses, home produced, commercial ones, etc : i ended to
buy a scraped terminal server allowing me to connect up to 40
traditionnal 9600 serial devices as well as 57600 bps modems (slip and ppp
can be provided by the termserver). It's dirt cheap when gaming with
sensors and actuators, and wiring is build around standard ethernet cables
with RJ45. But ethernet and IP compatibility with OpenBSD is total, and i
can totaly rely on the code already wrote by people hanging around this
list.
I buy sensors part by part when needed (through local retailers or
radiospares catalogue for example) and i glue that to the termserver using
8 to 40 pins Atmel AVR 8 bits RISC controlers (please have a look a
OpenBSD packages and ports when looking for dev. environment) and regular
MAX232 line driver. I don't need long distance connection but adapting the
link to optical, fiber-optic, or differential (R422/485) driver is quite simple.
The controler allows me to easily perform all acquisitions, calibrations,
and conversions from electricaly sensed values to physical values.
As regard cheap sensors, i prefer the old Philips H1 (capacitive gold film
sensor still available from some retailers) for relative humidity
(resistive Honeywell sensors seems also good to me). I simply prefer LM35
when dealing with temperature, and PT100 in more strict environment (i.e.
the area around my vegetables during all my shamefull fridge experiments).
Allegro hall effect sensors were easy to use as well as cheap. You can
find all the cheap sensors you want simply using a little bit of
imagination... and sometimes just by diverting the normal use of what you
already own within your spare parts. i.e. measuring the current needed to
immobilize a free moving "hammer" found in some electro-mecanical door-bell
may allow you to detect & quantify some movement or vibration. This kind of
sensor may be really cheap and efficient. Modems are also great thing to recycle
from junk yard as monitor for power supply before UPS. Power availability can be
sensed using an old 2400bps modem... there is an OK answer to any AT question
while power is here !
If you're projecting to monitor water quality... common available sensors
(like pH , resistivity, etc) will lead you to more funky interfacing...
far away out of the scope of this list. The cost will be higher whatever
you choose... homebrew sensors or commercial ones.
All of the sensors i listed just above can be handled using counters
within the local controler. There is no need of bulky and costly Analog to
Digital Converter. In the worst cases i sometimes use ADC, but one of my
favorite workaround is to use LM311 chip (Voltage to Frequency) or the
traditionnal 555 in one of its low consumption latest design when i try
to alleviate the headache about the connection to the controler. Then handling
a 16 bits counter is a simple joke for anybody.
On OpenBSD side... anything you can compile or script which allows you to
communicate over telnet can be used. There is no restriction here. I still
have no ppp/slip/IP stack for the controlers i use... i can't speak about
networking theses sensors. Someone on this list may be able to speak about
this ?
And... Hummmmmmmm... As regard the stack of junk code i am able to
introduce inside my controlers during all my experiments... i have a non
disclosure agreement with myself just to avoid any shamefull situation for
me. ;-) However ATMEL datasheets and application notes are clear enough
for any "apprentice".
All of this costs me more time than money during my experiments and
it's one of the criteria of my own game. One other criteria is reliability
because i don't like to repair failed parts i already built. And this
solution also fullfills it.
Regards,
Eric.
p.s. i know that it is not a develloper answer... just a basic user
answer... but no flame please :o)
