COVID 31 March Because of the current virus pandemic and various rules and regulations currently in force, effectively immediately, I will be posting orders only one day a week - Friday. That means, if you place an order on a Saturday, it will be another 6 days until it will actually get posted if you place an order on a Friday, it may or may not make the post that day. While this may be inconvenient and a nuisance, it is a necessary measure to protect the health of myself as well as others. As far as you are able, stay safe and remember, there is always the radio for contact with others. UPDATE 6 April It is apparent that postal services have been extremely badly affected by the current global situation and there are now significant delays in delivery times. You can check on expected delays at the Australia Post page here: Australia Post coronavirus international updates.
|Published (Last):||6 August 2006|
|PDF File Size:||14.77 Mb|
|ePub File Size:||20.31 Mb|
|Price:||Free* [*Free Regsitration Required]|
COVID 31 March Because of the current virus pandemic and various rules and regulations currently in force, effectively immediately, I will be posting orders only one day a week - Friday. That means, if you place an order on a Saturday, it will be another 6 days until it will actually get posted if you place an order on a Friday, it may or may not make the post that day. While this may be inconvenient and a nuisance, it is a necessary measure to protect the health of myself as well as others.
As far as you are able, stay safe and remember, there is always the radio for contact with others. UPDATE 6 April It is apparent that postal services have been extremely badly affected by the current global situation and there are now significant delays in delivery times.
You can check on expected delays at the Australia Post page here: Australia Post coronavirus international updates. From experience with the last few international orders sent out, the delays are around double what is being advised on the above Australia Post link. Hopefully everything is now back to normal but please let me know if anything is missing. The start of a new project added in the Homebrew category.
Specifically, a Frequency Dependant Switch. Measures the incoming frequency and switches 1 of 8 outputs on. Software for this project uploaded. This is an absolutely basic, no frills project using a 12F to sweep a DDS module between a range of frequencies.
As of October , I will be asking for a donation in exchange for providing custom modified code for my projects to help keep this site available.
Before anybody goes "well, why not run one of your rigs into a dummy load? Going out and buying a signal generator was not an option, especially when the nearest likely place that might have one is Kms away and worth far more than I had to spend. The Internet to the rescue.
Price was good too, especailly when you add up the cost of components, the pcb and the freight was free. For all intents and purposes, they look identical unless you have a magnifying glass in hand. Because I needed to get this done relatively fast, I again turned to the internet to see what was available.
My circuit diagram is shown below, along with version 1 of the pcb. I say version 1, because I must have been having a really good day when I designed it, I left some bits out! Click schematic for larger view. Click again to close.
I have redrawn a version 2 of the pcb, but have not as yet made it, so there may still be a mistake or 2 in it, but here is a picture of it for interest. Here are a couple of pictures of the board as it currently is. The LCD is a blue background with white characters type and the encoder the bit with the big silver knob partially hiding was a volume control from a stereo system.
And yes, I was still having a good day not when I made this pcb, as I made it back to front. One of the other things I need is a sweep generator to align my FT Luckily, while going through the DDS folder on my computer, I found a piece of software that almost fit the bill exactly.
A little bit of investigation and time later, the changes were made for the AD and again, it worked first time. There are a couple of things in the software that need pointing out. Update 17 May A quick update. This leaves two pins spare and if the MCLR in code is set to internal, that will give one more extra pin. The code version is 1. Led code has also been removed from this version.
Have also posted a modified version of the PicGen6 asm code and renamed to ver7. Here is the modified schematic. Click picture for larger view. Update 16 July One of the things needed for a signal generator, is to be able to adjust the output level to be a known quantity.
A pre-requisite is a signal of known amplitude, to which you can apply known attenuation. Along that vein, I have been playing with controlling the output of the DDS chip itself.
On these modules as they ship, that resistor is Ohms. However, on the midnight design solutions website, as part of the antenna analyser project, was a couple of ideas, one of which is shown below. To start with, the control range on the pot was extremely small anyone with a hand tremor would not have been able to set it at all , and it did not control the level very well over the frequency range.
So I tried various ideas using the other half of the LM, of which all were worse. Leaving it aside for a few days and doing some paying jobs for a change , I formulated what you see in this next schematic. There are two main differences to the first try. Firstly, the reference voltage for the adjustment pot was changed from the full 5v to approx. It helped, but the adjustment range is still fairly small.
Secondly, the ohm resistor was changed for a ohm resistor. Sadly, while the level of the output could be maintained over a small range of frequencies, it is still not satisfactory over the whole frequency range. The inbuilt low pass filter of the DDS module is partly to blame here. More info will be posted at a later date. So I have made a semi permanent development unit. It is made of some scraps floating around the workshop, a piece of aluminium sheet and a leftover bit of skirting board.
One problem encountered was how to mount the encoder. This is just a 35mm square piece of pcb material with the pads scratched out with a sharp knife. I only used two of the mounting holes, it is stable enough not to need all four of them. Here is some preliminary info on the output stage that I am working on. There are two amp circuits I am looking at. One using a BGA, which is basiclly just a mmic wideband amp from Philips. They were on special for a few cents each, so I got some to play with.
The second circuit uses an LMH, which is a current feedback wideband op-amp from National, now part of Texas Instruments. More to come as I get this prototyped. Despite all the dire warnings in the datasheet for the LMH about pcb layout, it works quite well dead bug style.
The IC is in there, right underneath the ohm resistor. It is connected to the DDS module directly after the filter and is being run off a 9V supply. With And just to show that this is a "working" workbench, here is a pic of the prototype hooked up in the only piece of clear space on the bench. It is a well known feedback style amp. It is perfectly legitimate to do so, but note that, depending on your actual components and building style, it may be unstable.
If it is, move the connection down to the collector of the 2N The only drawback is that the output level is reduced. In theory, this amp should have an input impedance of 50 Ohms, which is not a good match to the Ohms of the output filter on the DDS module. The result should be a distorted waveform into and out of the amp, but my scope trace showed no problems unless I played with the value of R6.
Going too low in value, while increasing the output level slightly, will distort the waveform, indicating a definite mismatch. I have yet to put this amp on the spectrum analyser, but adjustment of the R6 value should get you to a close enough match at the input. This will also shift the output impedance slightly, so, if you need a definite 50R output, add a 6dB 50R attenuator pad. There is a very good site for homebrewers that has much more information on feedbacks amps, measurements and a whole lot more, by Todd, VE7BPO link below.
This is where I got my inspiration to try this out. If you have not seen his site and are a keen homebrewer, I highly reccomend a visit. I am working on making the ver7 code work with a mechanical encoder. The main idea of this is to maintain a constant output level over the entire frequency range of the module. By 60MHz, it has dropped to -1dbm. The figures for the 2N stage will be added later. I have also drawn up what, for me, will be the final pcb of the DDS controller.
For those working in Imperial measurements, For those that may wish to make their own copy of the pcb, the file is in the Downloads section below. Please see the Homebrew Menu page for details of a free viewer that you can download and use to view and print the file. A note on the items marked as RFC.
DDS-Sinus-Rechteck-Generator mit AM von 1 Hz bis 40 MHz
We use a crystal oscillator of MHz and do not use the internal multiplier in order to increase noise performance. For the crystal oscillator a separate voltage regulator is available, in order to generate different voltages necessary for different oscillator types. We therefore decided to try to get away with an opamp. We have chosen the THSD from Texas, as it was in the treasure box :- Beyond that, nothing special, we follow the reference design from Analog Devices. This version 2. When using version 1.
Arduino based DDS Signal generator using AD9851
Auch diese gibt es in der Bucht. Die Anschlussbelegung selbst ist aus den Kommentaren der beiden nachfolgenden Bilder zu entnehmen. Die Beschaffung ist ebenfalls in der Bauteileliste beschrieben. Beispiel einer Verdrahtung des linken Drehgebers. Die beiden anderen sind die des Drehgebers. Der Stromverbrauch liegt bei mA.
Double click on code to select ...