Subject: From: Date:

Re: [ECS] Creating ECS interface to my Access Control System Brian McGinnis Mon, 23 Oct 2000 10:42:43 -0600

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Hi Kevin et all,

I just purchased some "Hot Little Therms" which are temp sensors built
around the Dallas chip.  I discovered them from another subscriber on this
list, I think Bill Freeman.  Anyways, they're very inexpensive, and one unit
supports a bunch of sensors.

They use a serial protocol to communicate with the unit.  At first, I wrote
an ECS event to poll the HLT device and stuffed the temperature readings
into text items, but had trouble converting the text items into usable
numeric items, especially negative numbers, plus the readings come back in
celsius.

So... I ended up writing a little utility program to sample the therms on a
user defined interval, do the conversion, and then pass the state values
directly to ECS via a DDE link.  This seems to work very well.  I created a
new custom item type that contains all of the possible values from
around -50 to +140 degrees (which, when converting from celsius, not all
tenths values are used.)

Now, whenever I want to add a new sensor, I just create another item with
this type in ECS.
I then tell my program what I've called it and what the ID is (Each sensor
has a unique ID).  After that, my program will attempt to update the item's
state whenever the polling interval has elapsed.

The program also "discovers" new probes and tells you the ID of them.  It
will also read from any number of HLT units and probes all connected to the
same serial port.

If anyone wants it, I'd be happy to upload it ftp.gallops.com/incoming.  You
can check out the HLT web site at www.spiderplant.com

The reason I bring this up, is that you could do the same thing with your
access hardware.  Write a program to take care of the dirty work, and then
tell ECS about it via DDE.  ECS can also talk to your program via DDE as
well.

Just a thought,
Brian

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