Neil - have a look at the Chinese AD9850 boards on eBay - around a fiver=20
delivered and range from 0.something to lots with plenty of resolution and=
=20
accuracy.

Sine wave output with a comparator onboard for square wave. Not a perfect=20
design but adequate for the majority of messing about. Can be accesses by=20
serial or parallel loading depending on how quickly you want to change the=
=20
frequency.

Bang in the right number for the frequency you're after and you're there.=20
I've been quite impressed with the unit I've been playing with.

Dom

-----Original Message-----=20
From: Neil
Sent: Tuesday, September 16, 2014 8:45 PM
To: Microcontroller discussion list - Public.
Subject: [EE] Digitally-controlled oscillator

Hi all,

I need to build a small test device that can generate, among other
things, pulses of specific frequencies.  And I'd like to control this
digitally (from a central PIC).  Specs would be basic 0-5V pulses, freq
from about 1Hz to 500Hz (higher is fine as I can divide with some
gates), and resolution of about 1Hz across the full range.  1% accuracy
should be fine.  And I need to be able to change frequencies very
quickly (say at least 20 times a second).

Any recommendations on chips that can do this easily?  Yes I can use a
PIC for this, but I just need a few of these and would rather just get
something off the shelf.

So far I've found the DS1077, but at a quick glance, I have to give it a
divisor rather than a frequency and in the low range of divisors it
seems I may not get good resolution.  IE: changing divisor from 2 to 3
would mean a 50% change in frequency.

Cheers,
-Neil.

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--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.