NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/sci/electron/19038

Internet Message Format | 1992-11-17 | 1.7 KB

Path: sparky!uunet!think.com!paperboy.osf.org!hsdndev!dartvax!coos.dartmouth.edu!bruce
From: [e-mail] (Bruce K. Johnson)
Newsgroups: sci.electronics
Subject: digital clock for circuit
Message-ID: <[e-mail]>
Date: 17 Nov 92 18:02:05 GMT
Sender: [e-mail] (The News Manager)
Organization: Dartmouth College, Hanover, NH
Lines: 28

Hello all.

I have a question about making a clock for my circuit.  First, let me give
you a background --- I'm making an A to D data aquisition box for the MAC's
serial port.  I'm using an ADC0831 chip and want to time it as well as provide
an external clock signal for the MAC's handshake line (the MAC can only run its
serial interface at a top speed of 57900 BAUD internally, therfore, if I want
to run say a 22 KHZ sample rate, I need a much faster ext clock...)

Anyway, I originally started off with an oscillator and a decade counter to
get the two clock signals (one that provides chip select line to the a/d at
about 22 KHZ and the other to provide the BAUD clock about 10 or 14 times the
first clock --- 8 bits of conversion plus a start bit plus several stop bits)

This costs too much.  My project is for use by students in a Physics class
and must be relatively inexpensive for them to purchase.  I then turned to
using a 556 timer to get two clock signals with one chip (a .70 cents chip
compared to a 1.70 osc + other stuff).  The 556 is capable of providing
a stable signal for the 22KHZ clock but not for the 220>KHZ clock.

Is there another cheap alternative to making two clock signals or can I make
the 556 (two 555 on one chip) produce a more stable signal at these high speeds?

Any advice would be greatly appreciated.

THANKS

BRUCE