Digital Circuit Diagrams+FETs+Drivers

[orbs]

As far as sine wave output, if that was desired, remember unidirectional concept.  The actual
output can easily tuned to emulate a perfect sine.

Sometimes it can even be easier to generate square waves from sine waves, which might seem strange at first. A DDS (Direct Digital Synthesizer) generates a sine wave approximation using very fast D/A converters. This approach allows to generate very finely tuned output signals with accuracy of fractions of Hz, and errors and drifts can be corrected digitally. The signal is then low-pass filtered to get a smooth sine wave. Putting this through a good comparator can then yield a square wave signal with almost perfect 50% duty cycle (because the used sine signal was perfectly symmetric). While such a DDS is more complex, most of it can be put on a single chip, and calibration and selection of the good chips is done at the factory and you don't have to do it yourself (but obviously you pay for it).

An example is the AD9912 mentioned in the other thread.

[MeggerMan]

@Orbs,
There is a whole thread on the DDS 20 kit from ELV in Germany. Cost is about 42 GBP/ 80 USD for the kit which is easy to build - only the big through hole components to add.
I translated most of the manual to English with my own interpretation of the workings of the DDS 20 based around the AD9835 chip.
http://www.overunity.com/index.php/topic,2650.msg38239.html#msg38239

I am currently working on a -5V inverter circuit to piggy back on the back of the DDS 20 board.

As soon as I have finished decorating the front room I'll finish it off (V1.1). (I promised Roberto 1 board and Ward 4 boards + 4Ã,  cases).


Here is V1.0 + circuit (I have not got a photo of V1.1).



Here's the DDS 20 squeased into a small ali case:


The kit contains this:


The only down side with this is the LCD display segments do not always show but you can sort this by using a neoprene bezel inside the case pushing the LCD display onto the PCB.

Regards
Rob

[Feynman]

Wow, great thread!  I really like the ideas of shift registers, dividers, and flip-flops for frequency synthesis.

@MeggerMan
Regarding this latest post, are they still not shipping these kits to USA?  I'd be interested in getting one. . .

[MeggerMan]

@Feynman
What I did for Ward was he sent me the money, I ordered the kits (6 of them) to the UK, I built the boards and posted them to the USA.
On one of the boards I found a fault with a tiny solder ball bridge on AD9835 that I found with my microscope, once I removed, it worked fine.

Jason is working on board with 3 x DDS chips, phase shift for each DDS, pulse duration control, opto isolation, MOSFET driver - in effect the works.
I think he's driving it with a PIC Stamp using basic.

I have most of the parts to build the AD9959 quad channel DDS, plus the low jitter 125MHz SAW oscillator.
BUT....its a big project, make no mistake and needs some complex PIC programming to pull it all together.

Soldering the AD9959 is the tricky bit, the chip is 8mm square, 56 pins, 0.56mm pin pitch.

I was considering buying some cheaper chips with a similar pin count and trying my PCB oven with different ideas.

Regards
Rob

[orbs]

There is a whole thread on the DDS 20 kit from ELV in Germany.

Thanks -- pretty cool stuff! Well, the AD9912 I mentioned is in a slightly different category (up to 400 MHz, jitter in pico-second range, etc.), more expensive and more difficult to solder. It's also pretty new, so no kits available yet. Possibly overkill for SM's design (compared to spherics' one).