[Elecraft] [QRP-L] DDS module

Thu Jun 27 15:18:18 EDT 2013

I'm in Charleston, SC, and my computers are shut down right now, due to 
thunderstorms and possible tornadoes.  Yesterday, we had a 7-hour power 
outage after a similar set of storms.  Thanks to a house generator, we had 
air conditioning, but I haven't turned any computers back on, other than 
this portable unit.  For that reason, I can't get to my information on these 
devices right now.

If you do an ebay search for AD9850, you will find MANY people selling these 
modules.  Within that group, there are some that have the schematic posted. 
Look at the pictures of each module, then look at the details of the devices 
on sale that match yours.  You can also find a few that have Arduino 
sketches, the same sketch will work for either type of module.  I have it on 
another computer here, but am concerned about posting it, regarding any 
possible copyright issues.

There are two types of there modules, I have a few of each type, along with 
a similar module that had an AD9851 instead.  The type you have has a 
smaller oscillator and very small pot, the other version has a larger 
oscillator, and a much larger pot.  Both types appear to have low-pass 
filters designed for the higher-frequency AD9851, as the LPF parts values 
are the same as the one on the AD9851 boards.

If I remember correctly, on your module, there is a discrepancy between the 
pin numbers/signals on the schematic and the board itself, on the upper two 
pins of the two-row connector.  I will provide more info as I can get to it.

A few years ago, I drove the AD9850 and many other DDS chips/modules using a 
PIC 18F2455.  This code was originally written by Tom, and was available on 
the DDS Controller Yahoo group, for QSD/DDS board by Dave, WB6DHW.  I went 
crazy and added support for many other DDS chips.

More recently, I've played with these modules driven by an Arduino.  There 
are a few web sites that have some basic Arduino skteches to drive these 
cheap DDS boards.

These modules are pretty easy to drive.  You need three signals, plus 
optionally a reset line.  The AD9850 can be programmed either by a series of 
eight-bit bytes in parallel fashion, or more often with a 40-bit serial 
bitstream (IIRC).  You drop the chip select (FQ_UD?), and set the data bit, 
then toggle up & down the clock bit.  Do that 40 times for the 40 data bits, 
then bring the chip select back up.  To set the AD9850 to serial mode, you 
also need to set a couple of pins to VCC or ground.  I sort of remember D7 
being one of them, but I can't remember the exact details right now.

Hope that helps some.
73, Terry, WB4JFI

-----Original Message----- 
From: Brian Pepperdine
Sent: Thursday, June 27, 2013 2:52 PM
To: n5ib at juno.com ; elecraft at mailman.qth.net
Subject: Re: [Elecraft] [QRP-L] DDS module

Bill Meara is playing with one and relating his experiences on Soldersmoke, 
his blog.
He has a few postings regarding it.
http://soldersmoke.blogspot.ca/search?q=dds

> To: qrp-l at mailman.qth.net
> Date: Thu, 27 Jun 2013 13:06:34 -0500
> From: n5ib at juno.com
> Subject: [QRP-L] DDS module
>
> When ordering some parts from an offshore vendor, I decided, on a whim,
> to add one of the little $5 AD9850 DDS modules to the cart.
> Arrived today, looks fine, but, as I fully expected would be the case, no
> documentation accompanied it.
>
> It was item 330840407981 from chipworld
>
> I wonder if someone on the list has been playing with this same module
> and has deciphered it.
> The good news is that the labelling on the board more or less matches the
> pinout in the 9850 data sheet.
>
> It measures 42 mm x 30 mm, has a single row 7-pin header on one end, and
> a dual row 14 pin header on the other.
> There's a 125 MHz oscillator can on board.
> The only ID-like marking is "19026AP4-24" (might be "19826AP4-24") right
> above the 9850 chip.
>
> I can send a hi-res image if you think you may have some insight.
>
> Otherwise, we'll take the datasheet and start tracing  :^))
>
> A receiver project is in the plans, and this is an excuse to write some
> PIC code to control the DDS.
>
> 73,
> Jim, N5IB
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