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SUMMARY AND LINKS OK, you've read the preceding pages and you're all fired up to rush out and build a DDS Synthesizer. Before you do anything rash let me bring you down to earth with a few facts about this project; 1. The hardware is relatively simple, this is perhaps the main attraction, and one of the biggest deceptions, about this type of project. The most complicated assembly stage is the mounting of the AD9850 chip. This is in a shrink package with very fine closely spaced leads. The chip is expensive, you only get one chance at mounting it and you must observe anti static precautions. Even with 20/20 vision you will need the steady hand of a surgeon and a magnifier to solder up the connections. 2. To program the PIC's you need to buy, borrow or build at PIC programmer. This is not a major obstacle there are many kits and designs available through electronics magazines or over the internet. To use the programmer you will need a PC (presumably if you're reading this you already have one) and the software for driving your chosen programmer. Open up each of the programs through MPLAB or Word pad and familiarise yourself with their structure and operation, they are well documented. Each program comprises of a main routine which calls a range of subroutines, the structure is very logical. The PIC software versions provided here are set up for a 10MHz IF Offset. You will need to change these to suit your own application, this is not difficult, use the Windows scientific calculator to covert your IF frequency from decimal to hex and over write the existing hex IF offset in the program using a text editor (Word pad) or the MPLAB complier program. If you plan to use the software for direct conversion applications you will not need an IF offset - simply remark out or delete the IF Offset call statement in the DDS Manager PIC (PIC 1). 3. When operating correctly there are a lot of transactions occurring between the PIC's, LCD and DDS. If your project doesn't work properly you will have to wade in and work out where the failure is. An dual beam oscilloscope is essential. You may be lucky and not have to resort to this, but just in case make sure you can get your hands on one.
Still enthusiastic? Good! Here are some links for further reading; http://www.njqrp.org This is where it all began, nice work guys! http://www.analog.com Home of the AD9850 DDS, and some very interesting successors http://www.microchip.com Everything you need to know about the PIC16F84 including software downloads http://www.nomad.ee/PIC/ David Tait of Manchester University complied a phenomenal amount of information about programming and PIC's. Sadly the University needed disk space and so his site had to go. There are any number of mirror sites around the world, a testimony to this chap's efforts. Give him a Knighthood! Watch out for more links as I discover/remember them Good Luck Ron Taylor G4GXO
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