[time-nuts] Clocking a PIC16F628A from a Rubidium Standard

Attila Kinali attila at kinali.ch
Thu Nov 24 09:50:29 EST 2011

On Thu, 24 Nov 2011 14:41:24 +0000
Stephen Farthing <squirrox at gmail.com> wrote:

> I have an Efratom 101 frequency standard with a 10 MHz TTL otput. I want to
> use this to clock a PIC 16F628A so I can make a frequency counter with a
> resolution of 1 Hz. I am going to use the design by EI9GQ here
> http://homepage.eircom.net/~ei9gq/counter.html . What I need to know is how
> i should go about electronically interfacing the TTL output from the
> rubidium standard so that it can clock the PIC. Has anyone on the list
> actually done this successfully?

Have a look at the PIC 16F628 data sheet, it will tell you the requirements
for the clock input and there should be circuit for external clock signal
listed. If it's not in the datasheet, it should be in an appnote.

Usually, chips accept sinusoidal and rectangular inputs up to 0V-VDD swing.
If i'm reading the schematic correctly and the PIC runs with 5V, then
you should be able to just feed the Efratom output directly to the PIC.
Maybe, a ceramic 100n capacitor in this line should be used to do
a DC isolation (1u cermaic should do as well).

			Attila Kinali

The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
		-- Tirin, The Dispossessed, U. Le Guin

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