Sounds like you are rereading the cached data, which makes the whole thing
seem faster if there are multiple clients for the same data. If you read
"mnt/1wire/10.(blah)/uncached/temperature" then you force a device read on
each access.
On 6/20/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
I've done some searching on google and within this newsgroup itself to try
and answer this question but haven't yet found anything so I figured I'd
ask in the hopes it's an easy answer.
I'm using a DS18S20 and a parallel-port-driven relay to model a furnace
control system: the DS is taped to a lightbulb the relay turns on and off.
The point is to get a decent PID tuning algorithm that can work with a
variety of furnace sizes.
The problem is that sequential samples of the DS indicate to me that I'm
not actually getting updated information, just the same thing I got last
time. I read /mnt/1wire/10.(blah)/temperature and get, let's say, 25.75
degrees, call it again two seconds later and get 25.75 degrees, call it
another three times and get the same number, then on the sixth call, get
38.2 degrees. It looks to me like the system isn't actually acquiring
information from the DS each time.
A: is there a way to force new acquisition with each request?
B: would +5V external rather than parasitic powered DS help?
C: is a two-second cycle time too short?
The hardware consists of a homemade diode-based RS232-onewire converter,
with a 30 cm long twisted pair going to a single DS18S20, which is
parasitically powered. The software is C; I'm using fopen and fscanf to
acquire the contents of /mnt/.../temperature and work with the results.
I'm not expecting microsecond conversion rates, but it'd be nice if I
could get updates every two seconds.
Thanks for any help.
John
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