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PICList Thread
'PIC as 50 MHz Frequency Counter'
1998\02\18@085412 by Miller, Steve

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Howdy,

I have located a copy of the Popular Electronics article from Nov 1994.  Please
note that this uses the PIC16C54, while the original thread was discussing using
the 16F84.  However, the firmware could easily be modified.    Mr. Weeder has
used an FET and a BJT as the input amplifying devices.  His article claims that
the sensivity is 100mV from 100HZ to 2MHZ and 800mV at 50MHZ.    The published
schematic contains at least one error.  The node connection of R2, D1 and D2
should connect to ground.  The schematic shows this node as floating. The PCB
artwork shows this node attached to ground.

---- Steve

1998\02\20@084049 by Peter van Hoof

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One little problem with the 16f84, it is only going to work to about 20 MHz

At a VSS of 3 to 6 v
Tt0h =30ns Min
Tt0l =20        ns Min

Below 3 volt it gets worse
Tt0h =50ns Min
Tt0l =50        ns Min
See page 81 of the datasheet

Meaning 20 Mhz with a 60% duty cycle at above 3 volt supply
16.6 MHz at a 50 % duty cycle

below 3 volt it would be 10 Mhz

Peter

----------
> From: Miller, Steve <spam_OUTstevemTakeThisOuTspamTANISYS.COM>
> To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject: Re: PIC as 50 MHz Frequency Counter
> Date: Wednesday, February 18, 1998 8:30 AM
>
> Howdy,
>
> I have located a copy of the Popular Electronics article from Nov 1994.
Please
> note that this uses the PIC16C54, while the original thread was
discussing using
> the 16F84.  However, the firmware could easily be modified.    Mr. Weeder
has
> used an FET and a BJT as the input amplifying devices.  His article
claims that
> the sensivity is 100mV from 100HZ to 2MHZ and 800mV at 50MHZ.    The
published
> schematic contains at least one error.  The node connection of R2, D1 and
D2
> should connect to ground.  The schematic shows this node as floating. The
PCB
> artwork shows this node attached to ground.
>
> ---- Steve

1998\02\20@191347 by Walter Crauwels

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Hi Steve
I would be verry interested in a 16f84 version of the software
if so please email the URL are the code and the schematic pse
Thanks
Walt

{Original Message removed}

1998\02\26@124609 by Brian Schousek

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To give an update to this thread: EDN magazine has a design idea showing
circuitry (sans input amplification) in their latest issue (march 2 1998,
should show up on the web in a few weeks if you don't get the print
version.) This uses a PICmicro and NPN transistor to duplicate the base
functionality this thread covered some weeks ago.

Brian

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