[time-nuts] PCB design questions

[Didier Juges]

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of David C. Partridge
> Sent: Monday, June 02, 2008 1:20 PM
> To: 'Discussion of precise time and frequency measurement'
> Subject: [time-nuts] PCB design questions
> 
> I've been working on the design for a frequency divider to 
> complement the Thunderbolt I recently bought from TVB (thank 
> you Tom, it's working very well as far as I can tell, though 
> of course I've no other standard to compare against).
> 

Dave,

I just made one using a single microcontroller chip soldered on a Toolstick
from Silabs. The Toolstick is a small PWB with a small 8051 class
microcontroller in surface mount package. The Toolstick costs $10 and you
need a $18 programmer to flash it. I run the uC using the 10 MHz as external
clock and it has (for now) a 1Hz output.

The toolstick I used is similar to the one described on this page:

http://www.ko4bb.com/Test_Equipment/AFSignalGenerator/SigGen.php

The software is just a couple of for() loops to kill time, a few 2 and 3
cycles instructions to adjust the timing perfectly (cannot do NOP from C
with the free compiler, but you can program in assembly if you need to feel
some pain) and one output is twiddled at the right time. The processor is
using the 10 MHz as clock. A single chip is all that is required, the chip I
actually used is a C8051F530-IT, which costs about $4 on the Silabs web site
(qty 1) and comes in a 20 pin TSSOP package (surface mount, but solderable
by hand). You really only need to connect 4 pins for that job, supply
voltage and ground, 10 MHz input and 1Hz output. Silabs has a couple of
parts that are available in DIP package, notably the C8051F330D (refered to
as the 330-GP) which is roughly the same core as the 530. If you buy the
bare chip, you will have to buy the programmer separately, so if you just
want to build a few simple projects, you are better off buying the
toolsticks.

You might want to add a D flip-flop to clean up the edge, even though I do
not know the jitter of the chip itself (I have planned to test it as well as
I can, but there are more projects in the pipe at the moment than time to
address them)

I am working on a version with both 1 kHz and 1 Hz outputs.

There are a few sine-to-square converters (clock shapers) on Bruce's page at


http://www.ko4bb.com/~bruce/

Didier KO4BB

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