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[DPRG] Frequency Counter Question

Subject: [DPRG] Frequency Counter Question
From: Earl Bollinger earlwbollinger at comcast.net
Date: Mon Sep 29 19:59:00 CDT 2003

Thanks for all the info guys. I think the timer gate may be off
The 74HC590 binary counters are positive edge triggered.
Looking at the signal with a scope shows a nice clean square wave. The
TTL output from the MAX038 is run through a 74HCT14 Schmidt-trigger hex
inverter to boost it up to 5v TTL levels.
The high frequency range 200khz to 22mhz looks to work very well, but I
am getting some instability on the lower two ranges, I'll have to tune
that some more.
I have a HP frequency counter and I use it to set the frequency so I can
work on the 8535 program for this.

Randy Carter may have hit on it, the counters are counting base 2. Thus
LSB would count up to 255, then carry to the next counter which can
count up to 255. Thus xFF times xFF (255x255) is the maximum binary
count. So maybe I am screwing up the math then. I was taking the LSB and
MSB binary counts and sticking them into a WORD variable to set the
value, thus I might be messing it all up math wise. 
I'll have to ponder this a while.

-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org] On Behalf
Of rten at new.metronet.com
Sent: Monday, September 29, 2003 12:56 PM
To: Clay Timmons
Cc: dprglist at dprg.org
Subject: RE: [DPRG] Frequency Counter Question

Good analysis!

On Mon, 29 Sep 2003, Clay Timmons wrote:

> Earl,
> All your math looks right to me
> 1MZ signal at 10usec gate = 10,000 counts
> 10^6 cycles/second * 10^-3 second = 10,000
> But you are getting way more counts than that.
> Are you counters counting on the rising edge, falling edge or both
> Also make sure that the signal going into the counters is a clean rail
to rail swing with no bounces or noise.
> Later,
> -Clay-
> > But then the big question is....
> > Does this sound right or have I gone insane at the moment?
> > I amgetting something like 49,652 for a count at 1mhz (really really
> > close though something like 1.00034565mhz). Maybe I have the timers
> > wrong.
> > Or do I?
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