Re: Looking for Temp and humidity sensors

[Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Sun, 08 Jan 2006 23:33:00 GMT, nobody@xxxxxxxxxxxx (Dave Houston) wrote
in message  <43c19de1.227483796@xxxxxxxxxxxxx>:

>"Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:
>
>>Why *IS* that?  I was dismayed by the price and the restricted function of
>>the ADI "Bobcat" line of temperature and humidity sensors.  I see that
>>Worthington has some very cheap sensors listed with their ADI, HAI and ELK
>>offerings.  I would ideally line to monitor temperature and humidity info
>>for perhaps 20 different points in the house, with a wide array of
>>temperatures, too (chimney temps, hot water heater, fridge, etc).
>
>The Bobcat temperature node includes a power supply, an RS485 interface, an
>ADC chip (I think they use a PIC but it's been a while since I looked
>inside one), an enclosure and an LM34 temperature sensor.
>
>The Bobcat humidity node includes all of the above but with a Humirel
>humidity sensor replacing the LM34. Humidity sensors are not cheap.
>
>If you try to duplicate the design you will find that you really cannot
>build them and sell them through distribution channels for much less than
>what ADI charges.

The _fundamental_ problem is that Ocelot is stuck with an 8-bit Analog to
Digital converter which is a major obstacle to wide-range, high resolution
temperature measurement. Adicon's expensive solution is have more smarts in
the module and transmit the data digitally.

One better solution is to use an apppropriate logger/controller in the first
place. Environmental data loggers have been around for decades. I don't know
of a single one that is limited to 8-bit resolution -- for good reason.

>If you already have some type of controller with ADC inputs and a power
>supply and a little knowledge you can DIY and save (if you conveniently
>ignore the cost of the controller). The cheap sensors need something like
>an SECU16 or other controller.

The SECU16 is the same kettle of fish.

>I think your plans are overkill but you should look at some of the one-wire
>interfaces which allow you to network lots of relatively inexpensive
>sensors (at least for temperature, RH is still not cheap).

Did you know that you can monitor multiple locations in a home with a
*single* humidity sensor. And also detect smoke. And monitor volatile
organic compounds such as gasoline, and natural gas. And ....

>You still need some type of controller or PC to make sense of the data.

ROTFL "Overkill" for what? The fish are already dead when you choose the
Ocelot and try to kludge a solution for its shortcomings for this task.

( "When all you have is a hammer, everything looks like a nail." )

Yes, you need to be able "to make sense of the data". And once one moves
beyond using the data to define a threshold for action in real time
(Event-based trigger in ladder logic ala Ocelot and other current HA
controllers),  this requires being able to store the data which the Ocelot
and SECU16 are next to useless for -- current efforts for a fix
notwithstanding.

... Marc
Marc_F_Hult
www.EControl.org