Tuesday, January 14, 2014

DDS VFO

dds vfo without pic
I have seen this ckt diagram on the hanssumers website.

http://www.hanssummers.com/dds.html

We also have the ready made AD9850 or AD9851 modules available in the ebay and from hams. Sometime we need just one spot frequency and xtals are not available or economical. If anyone can help me make the ckt modifications for the ebay module, it will be a great help to all community. It is not economical to buy the IC alone. Readymade modules costs less..... please modify the ckt for ebay modules......

Well, my request on the facebook did give me few inputs. 

I got one very positive thing from riyas vettukatti

Riyas Vettukattil I guess you can use it with ebay modules. For eg if you want to make a fixed frq of 7050, calculate the 32bit freq word by going to http://designtools.analog.com/dtDDSWeb/dtDDSMain.aspx (choose ad9850) and the circuit above does the job of loading a 40bit (last 8 for phase is constant from Q0 output from the 4017) These DIP switches can be toggled to make a binary representation of freq eg : 7049.99 = [00001110 01110000 00111010 11111011] good luck Indrajit Sinh with tweaking..

then,Om Niras VU3CNS,  also gave one point that it is possible to port this thing to the ebay module. 

From ebay there are two modules. the modules i use is as given below. first one.
AD9850 modules






 Another ham has used this module with microprocessor but, here i am concerned with pin layout of the ebay ad9850 module.

The ebay module contains 125 mhz oscillator, rf filter. so what we have to do is give the controll words, clock etc. beauty of this module is that all the data pins D0 to D7 are in single line. so , easy to use, in the ic these things are on different pins. A single ic cost more than the module cost. Ic being in a small package is very difficult to solder on pcboard. So, it is nice to have ready made thing.

This is the famous dds60 daughter board. for the information i have put it here. 











*********************************************************************
THEN browsing on the net i got two little write-ups.May be that will be also useful reading. Time proven cut, copy, paste tech is used.

 1. from website www.theladderline.com

 ...AD9850 DDS modules
Submitted by VE2UM (not verified) on Wed, 11/09/2011 - 07:09. Nov 09 2011
Hi...

I discovered REALLY CHEAP AD9850 DDS modules on eBay...

Simply goto EBAY and type: DDS module

There ate PLENTY of them !!!!

There are more expensive COMPLETE signal generators at around 60 $ but the modules i talk about are the ones with a square blue pot, a square 125 MHz quartz oscillator and an LED close to the oscillator. Those modules can be bought for less than 12 $. I bought one of them, breadboarded it with a PIC12F1840 for initial tests (serial access) and it works great !

The only problem is that documentation on the modules is inexistent. I examined the module and found this pinout (quartz oscillator on the LEFT)

Top and bottom rows:

Vdd D0 D1 D2 D3 D4 D5 D6 D7 GND

Vdd CLK Latch DATA RST GND SQW SQW SinA SinB

Vdd is +5V (chip can work at 3v3 but not guaranteed to work at 125MHz)

D0 - D7 = Parallel programming bits

GND = Ground (obvious); Vss

CLK = Serial programming clock
Latch = Serial programming latch (FQ_UD pin on 9850)
DATA = Serial programming DATA (internally tied to D7)
RST = Reset. Keep tied to GND
SQW = Square wave outputs (complementary) Duty cycle adjustable with blue pot.
SINA = Raw unfiltered AD9850 sine output
SINB = 70 MHz LPF filtered AD9850 output.

I only tried serial programming. For that purpose, D0 and D1 should be tied to Vdd and D2, to Vss. Keep D7 open, I left D2 - D6 open, but note sure about recommended pin status.

The format is:

W0 W1 W2 W3 W4 W5 ------------- W28 W29 W30 W31 0 0 0 0 0 0 0 0

The frequency word has 32 bits, W0 is the LSB and W31, the MSB. W0 is sent first.

The last 8 zeroes are for the two control bitys (keep at "0"), the powerdown bit (keep also at "0") and the five phase bits that i keet at "0" for now.

The frequency word calculation is:

WORD = Frequency * 4 294 967 296 / 125 000 000

I used 125 000 000 for the nominal quartz frequency. The quartz oscillator in not a TCXO and is NOT adjustable. For greater accuracy, you shall read the actual quartz frequency and use it in the formula.

Example: for 3750 kHz: WORD = 3 750 000 * 4 294 967 296 / 125 000 000 = 128 849 019

in HEX: 07 AE 14 7B.

The frequency resolution is 0,03492 Hz, so you can build a really smooth VFO with the AD9850.

Remember: This is a DDS. While the signal is not bad (use the filtered SinB signal), it is not perfect. If you want to get on the air, you will need a lowpass filter for your band to prevent interference.

*********************************************************************
-then another write-up is here
---AD7C
I was browsing eBay one day and I ran across a posting for the Analog Devices AD9850. The AD9850 is a chip that can produce a sinusoidal wave from about 1hz to 40mhz. Somehow the electronics dealers in Hong Kong have been able to mate the chip to a small board that provides TTL level control and then sell it for an unbelievable $8 (or less!). I know a few people have paid as little as $4 (USD) for them.

AD9850 Module-

To control the AD9850 you’ll need some sort of micro-controller.  Without going into too much detail you are required to send a set of serial or parallel data to the chip to set the frequency.  There are numerous postings on the web detailing exactly how to do this so I won’t go into too much detail. However it has been hard to find a good AD9850 Pinout so here you go.

D0 – D7 = Parallel programming bits
GND = Ground (obvious); Vss
CLK = Serial programming clock
Latch = Serial programming latch (FQ_UD pin on 9850)
DATA = Serial programming DATA (internally tied to D7)
RST = Reset. Keep tied to GND
SQW = Square wave outputs (complementary) Duty cycle adjustable with blue pot.
SINA = Raw unfiltered AD9850 sine output
SINB = 70 MHz LPF filtered AD9850 output.

*************************************************************************

Now,enought of theory and it is time to solder the DIP Switch and then go for this ebay module.

Today 22 Jan 2014 around 2230 ist ,my friend rias gave me a link on his webpage where he has tidy-up the ckt removing the QRSS part. his address is http://blog.riyas.org/

dds vfo without micro-processor

Now, soldering and end result will be published may be within a week. 
25Jan2014 I was very busy in the family and Mqth so could not start soldering. As the first phase diode matrix is ready.
In the vero boards there was not enough space, so i had to join the  two 2030 modules. all diodes have been given the enough spacing so that it can be soldered but on switch8 diode is mounted vertically as there was lack of one dot space ! I have not soldered the DIP SWITCH with the intentions to use it somewhere else if the project fails. It also facilitate the easy switching. 16 pin Ic pad is soldered, so that soldering becomes easy. Care has been taken to put diodes corretly one by one. Put it, solder it, test it. then go for other diodes. so it was a very tedious task. it took me more than two hours time. once done will solder the gate oscillator and counter ics. So this will become my diode matrix for dds vfo controll.  please wait.......


 1 feb 2014:- Progress is steady but slow. finished up the diode matrix. oscillators. Now connection between two pc boards is to be done. drawn the module top side view. This module has the beauty that all the parallel data port is one side and diode matrix  also  matches it. wow !

Now, power supply needs to be made for 3.3v dds board and 5 volts for 4017 board.

 As of 05feb2014 finished almost all the wiring. I hope when this works a pcb is made so within an hour this can be soldered and usable.

Still needs to figure out what is the LSB and MSB and wethere 3.3volts to ebay module and 5volts to the counter ic will work or not.I hope it becomes reality and then with it will try to run a homebrew dsb transmitter.


8Feb2014
 

Results is:- Working. End of all my doubts. Ebay module is also working. This is a lengthy and tiresome work, making it on veroboard. It is better done on a etched pcb and within an hour it can be up and running. Will ask someone to make pcb. First problem low frequency oscillator(74hc04)and counter (74hc4017) is little wobbly. needs to be retuned or redesigned with other parts.
It works. All fine details and how to run it, will be uploaded after making few  more test and based on further experiments results. Will upload the circuit diagram.

End of the post. thanks for being with me.

Thats it folks ! we have just tried to re-invented the wheel. :) but failed....
have look at second part at
http://vu3inj.blogspot.in/2014/02/dds-vfo-ckt.html

2 comments:

  1. Good start! if things goes well, some of the Dip swich can be replaced with fixed connections/jumpers :-) can try with a high value with 7hc04 to check if the decade counter works in correct sequence (to clock at a low frequency )

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  2. i basically search a different topic ►­¹◄ (was googled to this website) . . . i don't get it - they use ►²◄ a ±750mV 12V OCXO VCO ³IC where the datasheet does not provide output stage schematic nor DC offset ... (insane) ... however by MAXIM´s VCO we can assume the GOLLEDGE´s IC³ may also have a DC decoupling internal capacitor - through which the +12V ÷ 2 = +6V (to Gnd) is seen from outside the OUTP ((i assume ??!! and then we drop it by 5.4V dn2 +600mV (a voltage drop on BJT´s BE) . . . and it (what we drop there) is a 50Ω impedance sine wave))

    + the triple uneqal "half"-cycle 74HC04 oscillator outputs it´s ωCLK from capacitor or basicly from it´s two "internal" inputs (that are visible to "external" ~AC) ??? why they use the expensive OCXO there ???

    ¹►https://escies.org/download/webDocumentFile%3Fid%3D62209&rct=j&q=&esrc=s&sa=U&ved=0ahUKEwjih5fZ_cTLAhXJC5oKHcyFDTkQFggZMAE&usg=AFQjCNElnBjoYhdtjBPKAUZWe1DezpRv4w◄

    ²►http://pdf.eepw.com.cn/h20090831/cf7fe29605846e22da90168a43079fd1.pdf◄

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