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[ts-7000] Re: reading pulses in realtime

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Subject: [ts-7000] Re: reading pulses in realtime
From: "Mike Dodd" <>
Date: Wed, 30 Mar 2005 17:15:35 -0000

> Thanks for your reply. Too bad, I was kinda looking forward to
> learning Linux.

Dan, before you give up, you might want to buy a TS-7250 and give it a
try. While Linux is not a real-time OS, it might be good enough for
your application - that depends on how fast your pulses are coming in,
and what happens if the system misses some of them.

Last weekend I was running some preliminary tests for my real-time
application, and the results so far look encouraging. I'm trying to
detect signals that can change state up to 25 times per second. The
combined waveform looks like this:

__A_____A_____A_____
_____B_____B_____B__

Each line can have 25 pulses, so really we're talking about 50 pulses
per second. Furthermore, the zero-states between pulses are important,
so they need to be resolved as well.

When the "A" bit goes high, my test app lights the red LED on the
board, and when "B" goes high, it lights the green LED. Ultimately it
will send two-character strings over an Ethernet socket to another
TS-7250, which will decode the strings and duplicate the signals on
the DIO port.

I still need to implement the full Ethernet interface and set up
counters in the transmitter and receiver boards, then let 'em rip. If,
after several hours, the counters are still in sync, I'll be convinced
the idea will work.

50 pps is equivalent to 3,000 revolutions per minute. How fast will
your wheel turn? Linux might cause your app to miss some pulses. what
happens then? That is, will a "speed indicator" dip momentarily, or
will it throw some hardware out of sync and crush someone's finger?

I hope this helps. Personally, I think it's worth a shot, especially
if you're designing a low-speed, non-critical system.

Mike Dodd






 
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