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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Mon 29, 2017 2:03 pm 
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While I was writing the documentation, I came across a possible confusing inconsistency that I wanted to make sure got cleared up. In the process of modifying the DDS2 generator board, the modifications specified in the article I referenced were both not real clear and confusing. I recalled that I had some difficulty interpreting that when I built my board. So here is a complete and hopefully clear explanantion.

First, the circuit diagram of the module and a link to the application note which explains how to do the AM modulation.
AN-423 PDF -> http://www.analog.com/media/en/technical-documentation/application-notes/AN-423.pdf

Image

Now I will repeat and modify the notes from the article that I referenced above on the module board modification.
http://www.nomad.ee/micros/rfgenerator/

First is to bring the RSET pin (12) out to connector. To free up the pin you have to cut the trace pin labeled as DATA, which is the same as D7 so you actually are not losing any signals. Once the pin is disconnected, its just a simple matter of soldering a wire from 3.9k resistor R6 pad to the freed up DATA pin.
Now in the article I referenced, the author does not remove R6, but I did because it is NOT sown as being maintained in the AN-423 document. Indeed, it does not make sense to leave it in because the FET now handles the current to the IC to provide gain control. If that resistor is left in, another 3.9K would be in series with the FET and that is clearly not in the AN423 diagram.
This shows where to cut the track under the board. Cut the trace where the red arrow points:

Image

Second mod is to bring the current output pins directly, without load resistors connected to them, out of the board so that they can be hooked to to transformer as shown in application note. The output filter on IOUT output (pin 21) also needs to be eliminated. I simply removed all filter components and load resistors from the board, the list of removed parts is R4, R9, C1, L1, C2, C3, L2, C4, C5, L3, C6, C7, R5. I used a fine needle nosed pliers to crush and remove the components rather than risk de-soldering and damaging other components or causing solder bridges all over the place. Then to connect the IOUT to ZOUT2 pin of the module you simply solder a wire from a pad closer to board edge of R4 resistor to pad of R5 resistor, also closer to the board edge. Don't worry if you accidentally bridge the solder to the pad of C7 since R5 and C7 are connected on the board.

This is how the board looks after both modifications:

Image

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Tue 30, 2017 3:17 pm 
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More changes to the parts list

Got a PM asking about the spacer and standoffs.
On Mouser, I found these parts which should work.
http://www.mouser.com/ProductDetail/Keystone-Electronics/2210/?qs=sGAEpiMZZMtrde5aJd3qw3QaZpWtG6niV8QxciOOZ4s%3d
http://www.mouser.com/ProductDetail/Harwin/M20-7820842/?qs=sGAEpiMZZMs%252bGHln7q6pmzlZUuX%2f53qjv4D%2fDP12Dqs%3d

And, a problem with the knobs. I ordered the ones shown in the BOM and they have the wrong shaft and are very loose. I need to check the shaft size and pick out other knobs. If someone ordered these already, I apologize. I did not check the knobs until the other day and it was a big "RATS!"

The shafts of the knobs I ordered were 1/4" D-shafts. The pots and rotary encoder are 6mm D-shafts. So that did not work well. I found the same type of knob in a 6mm shaft and corrected the BOM. Also added in the header and the spacers. The new BOM is posted and is available here:
http://louhaskell.com/data/generator/generatorBOM.pdf

Sorry.

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Tue 30, 2017 5:14 pm 
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Thanks Lou!

It appears the large knob is currently backordered in black, but it shows clear is available.

It also shows there is a cap to add to the knob. Either red or blue

http://www.mouser.com/Search/Refine.asp ... =450-AA150

-Steve

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Tue 30, 2017 5:27 pm 
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Thanks for that , Steve. I am not wedded to these knobs that I found. I wanted to fins something quickly so I posted the first thing I found . If anyone else finds a better knob, please post. The rotary knob really needs no marker rule so I tried to find one without that. This one has a cap with a marker so fine if that is OK with you. Maybe it would look nice with some vintage knobs?? ;-)

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Tue 30, 2017 11:35 pm 
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Lou, thanks for continuing to update the thread, and for providing all of the information, I got my board today, and it looks as good in real life as it does in the photos. Thanks! Now to order the parts.

Colin


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 12:05 am 
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Good deal, Colin. Be sure to ask any questions if anything is confusing. I am working away on the user guide and will publish shortly the first draft.

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 1:26 am 
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Your project turned out really well. Very professional looking.

I've used PIC controllers on my past projects, but given the low price of the Arduino modules and all of the good programming tools available, there doesn't appear to be much reason to stick with PICs anymore.


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 2:14 am 
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Hi Lou
My board just arrived in the mail to day. Nice board!
I have a lot on my plate right now (honey do) but will be ordering parts soon.
I have a question about the TFT screen. When I went to Amazon to order it they are saying that one is no longer
available. I found this one on Ebay http://www.ebay.com/itm/191816725599?_t ... EBIDX%3AIT Do you think it will be a good sub? I would like to find one here in the USA.
I tried to find one on the open web but could not find the exact same one.
Anyway let me know what you think when you get the chance. I know you are busy with a lot of other things and I am
in no hurry.
Thanks again
Bill

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 3:11 am 
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Bill, that board looks compatible to me. Same controller chip and looks like same form factor.

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 5:11 am 
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Location: Benton City, WA
Lou, my board arrived today also. Does the AVR code automatically resize for different display sizes (2.2 to 3.9 inches)?

Thank you.


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 12:05 pm 
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Southerner:
The LCD that I am using has a display area of 320 by 240 pixels. The issue for your display is whether it has the same number of pixels. It also must use the 9341 driver chip. The LCD driver I am using does have 320 X 240 hardcoded into it. However, I believe that can be changed. In my code, I have all of the sizes and positions spec'ed in #define statements at the top of the code so that can be changed in one place. The only 3.9" display I saw on the internet (after admittedly a brief search) was a 480 X 128 aspect. If you use this, you will need to rearrange the whole position of each item of the display. If you are familiar with Arduino code, I have published the software now and you can check it out yourself.

Of course, another issue is mounting. That display will be larger and hence not fit on the PCB so I guess you are mounting it separately with a cable between the board and the display? Also if that is the case, you may need to panel mount the pots and wire them over to the PCB, I expect. That is no problem I suppose.

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 3:28 pm 
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Lou,

A couple of questions about the BOM. R5, R7 are shown as 50 ohms, but the part number is actually for 51.1 ohms. R12, R13 are listed as 2.2 meg, but the part number is for 2 meg. I am assuming that the values are close enough?

Also, I noticed that the part number for R15 is wrong, it comes up as a 274 ohm.

Colin


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 4:45 pm 
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For the 50 ohm and 2.2meg resistors, I found small 1/8 equivalents to spec so they fit nicely on the board.
So yeah 51.1 is close enough as is 2 meg for 2.2 meg.
However, good catch on that R15. It really needs to be 100K and certainly not 274 ohms.

The correct part number is - 594-SFR16S0001003FR5

I just updated the BOM so accessing that again will get the updated list.
Thanks for finding that!

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 6:42 pm 
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Thanks Lou,
I did not catch the resistor issues as I chose not to order them. I have easy access to such resistors.
If I don't have some, then Midwest Surplus almost certainly will. :D

-Steve

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 7:45 pm 
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Yeah, Steve, I expect that most of us have lots of small parts around. I did spec the smaller 1/8 watt jobs which fit nicely as you see in the photos. I expect that the modern film 1/2 watt resistors may work as well. Depends on size.
So be aware of that.

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 8:06 pm 
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Lou,

I am puzzled. You mention 1/8th watt resistors, but it looks to me like the Mouser part numbers are for 1/2 watt. Am I misunderstanding something here? They will probably just fit, as according to the spec sheet the length is 5mm. I will find out when they arrive.

Colin


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: May Wed 31, 2017 8:18 pm 
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Colin, you are correct, they are 1/2 watt. I was assuming that they were 1/8 watt or 1/4 watt since they are so small.
But on review, they are indeed as you say, 1/2 watt.
The issue I was wanting to bring up was the size which is 4 or 5mm which makes them easier to fit on the PCB.
Thanks for clearing that up.

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Jun Thu 01, 2017 6:27 pm 
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I have been working away on the User Guide to help with both construction and operation. I have the first draft version available as a PDF for download here
-> http://louhaskell.com/data/generator/generator-user-guide-v0-1.pdf

It is still rough but useable I hope. I am adding figures for typical displays although I am missing some and will need to run some more alignment operations and take more photos.
Parts of the manual need more work. And some things came out weird, e.g. the schematic in the Appendix is unreadable for some reason. I am using the Apple Pages program and not Microsoft Word since I use a Mac. There are some differences that I am getting used to and some maddening problems like how best to place photos in the text.
Updates to come in the future.

Also, I know there will be some software updates. For example, the way the Bias is set for the input circuit is a kludge. I use the value of 0 to 9 to represent a voltage of 0 to 4.5 volts. It was easy to code for now until I take the time to use 2 digits for the display as it should. I also have the Rate as a sort of backwards value, i.e. 0 is the fastest and 9 is the slowest. I should fix that "someday".

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Jun Thu 01, 2017 10:15 pm 
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OK, I figured out why the images were so lousy inside the PDF user guide file. Here is an update with a little more content and better image quality. You can actually read the schematic in this one.

http://louhaskell.com/data/generator/generator-user-guide-v0-2.pdf

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Jun Thu 01, 2017 10:58 pm 
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A well-written document. I have all parts on order, so once everything gets here, including the display from Hong Kong, I should be ready to start the build. Looking forward to it!


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