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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Thu 16, 2017 6:23 pm 
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Looking good from here!

I don't think this will be nearly as heavy as my HP 8656B - or the HP 606B I wish I had! :D

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Fri 17, 2017 12:06 am 
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Looking good!!

Colin


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Sun 19, 2017 5:50 pm 
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In the last few days, I used the device to do a sweep alignment of an AM radio. I did a few more code modifications as I worked on the alignment.
Specifically, after reading multiple posts on the forum and experimenting, I realized that a slower sweep of the IF frequencies was in order. This allowed for a better visual as well as audio indications of the proper center frequency as in came to the center of the sweep. So I added a new feature called "rate" which varies the sweep rate. The max is now still 70 sweeps per second or so and the slowest is now about 2 seconds. In addition I added a variable marker delay that can be more easily seen on slower sweeps. That can also be more easily heard.
I included here a photo of the 455kHz sweep on my small Arvin 544 AA5 radio plus a YouTube video showing both visual and audio to see how it works. I had read some posts where some have said that AM sweep alignment is really not useful, but rather a simple single frequency peaking is all that is needed. In this case, I could readily see that the 2nd IF was peaking at a higher frequency than the first IF. So I could adjust each in turn to see a single peak at 455kHz. I thought that was very useful.
Here is the link to the YouTube video https://www.youtube.com/watch?v=wlvsXhqoM3U and the still photo is below.
Since I took a tap at the top of the volume control for this radio, the DC level for the AGC is also present. I expect 2 comments from you guys on this I suppose. First of all, when doing alignment, the level should be low enough to not trigger the AGC. Agreed. Secondly, It may be best to stick a capacitor in there to knock out the DC component and just show the AC. Agreed again. However I was surprised that , from the photo, the frequencies just below the center produced a not too dissimilar audio output.

Next up is design of an input circuit to the ADC pin 0 of the Arduino and coding for the internal scope display on the LCD screen.

Image

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Sun 19, 2017 6:56 pm 
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It looks good, Lou. I will have to learn how to use this device, once built. I have only ever used the "tweak the IFs for maximum output" technique (and I haven't done many of those). Are you going to do an FM alignment also?

Colin


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Mon 20, 2017 3:43 pm 
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Lou,

A question: what type of rotary selector are you using for function and frequency? Is it an encoder? I saw a really cheap Gray code encoder with switch at M. P. Jones:
http://www.mpja.com/03-20-17.asp?r=391886&s=11

Would this work, or are you using something different?

Thanks,
Colin


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Mon 20, 2017 5:01 pm 
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Colin, 2 answers for you:
1. Yes, I plan to do an FM receiver so that I can test the process at 10.7MHz and also make sure I can see the famous "S - curve".
2. That is basically the rotary encoder I am using. SInce I have Amazon Prime, I tend to try to get things from there (or Mouser if they do not have it). This is what I bought - https://smile.amazon.com/gp/product/B015QSIRPK/ref=oh_aui_detailpage_o07_s01?ie=UTF8&psc=1

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Mon 20, 2017 10:49 pm 
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Thanks Lou. I looked at the ones you bought, and they look better. Are you at a point where you could put together a list of the major hardware components, or is it too early for that? I ask because it might be better if I split the purchases into smaller lots, rather than trying to justify a large one-time purchase to She Who Must Be Obeyed!

Colin


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Tue 21, 2017 3:42 am 
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Wow, dramatic progress since I last checked this thread!

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Tue 21, 2017 1:40 pm 
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As requested, here are some of the major components that are used, i.e. the big ticket items. I will also indicate where I got them and possible alternates.

1. Arduino Pro Mini. - $7 - This requires an additional UART and USB connector board for $7 but I had one. I wanted to use an Arduino Nano but the one I have is a cheap one that will not download on my Mac. But a Nano would be best since it has a USB download port built in
https://www.amazon.com/Arducam-Atmega328-Development-Compatible-Arduino/dp/B01981EBBA/ref=sr_1_2

2. DDS 9850 generator board - 2 @ $17 - There may be cheaper one's out there. I got this one since I do Amazon a lot as a Prime member.
This is used both for the sweep and the function generator so 2 are needed.
https://www.amazon.com/gp/product/B0085N592S/

3. 5V wall wart ($7 ?)- will need this in the final version when not running from USB power. I bought a 2 pack since I need another. One is needed.
https://www.amazon.com/gp/product/B018WWI39W

4. MCP4801 DAC - $1 - This is the DAC chip. Cheap. Just showing it is not "big ticket" so can order that with other small components.
http://www.mouser.com/Search/ProductDetail.aspx?R=MCP4801-E%2fPvirtualkey57940000virtualkey579-MCP4801-E%2fP

5. Enclosure box - $7 - I found this box that I will use. I am sure there are others. I am concerned this is plastic so not sure if that will mess up and leak RF. But my prototype board is all "hanging out there" and it works. ;-)
https://www.amazon.com/gp/product/B005473R5E6.

6. BNC connectors - $6 - I got this batch and have not hooked them up yet. Looks they are currently not stocked. Need 5 or so I think by the time the design is done.
https://smile.amazon.com/gp/product/B012EELQK2

7. LCD screen - $10 to $40 - This is a troublesome device to get right so be careful. I am using a 2.2" LCD TFT SPI 240 X 320 device, no touch screen. There is a SD card reader on the back I am not using. There are many, many variant of this and some will work and many will not. I got mine 2 years ago from China off eBay or Banggood, don't recall where. Here is a link to Banggood showing what it looks like. Must have one that uses 9341 controller chip.
http://www.banggood.com/2_2-Inch-Serial-TFT-SPI-LCD-Screen-Module-HD-240-x-320-5110-Compatible-p-912854.html?rmmds=search

8. Rotary Controller - $2 to $6 - I bought a bag of these cheap and they work fine. Just a single can be found I am sure.
https://www.amazon.com/gp/product/B015QSIRPK

OK, so those are some of the major parts. I plan to use one of the schematic drawing tools and draw up the schematic so far. I am still working on an op-amp input circuit for the internal display version and I can add that later. I am using some $1 op-amps and small discreet so it will not add much to the cost. I have also started to look at PCB suppliers. I am sure that the cost will be much smaller if multiple boards are made at once. If folks would want one, I could see about supplying those "for a small fee" ;-) I would use a protoboard unless the PCB could be less than $20 or so. If anyone has a great supplier, please chime in.

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Tue 21, 2017 3:54 pm 
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Many thanks for taking the time to compile the list. Very helpful. I think the only part that will take some research is the display, as Banggood don't have any.

Regarding a PCB, I got good service from farcircuits http://www.farcircuits.net/ when I organized boards for an AM synthesizer project:
http://antiqueradios.com/forums/viewtop ... 2&t=285198
He accepts files done in ExpressPCB format.

Colin


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Tue 21, 2017 5:21 pm 
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If you go to Ebay and search for "ILI9341 controller display" it brings up quite a few listings.
Note that the first three characters in the part number are letters, not numbers.


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Tue 21, 2017 11:49 pm 
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Thanks Bob.


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Wed 22, 2017 4:18 pm 
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After I sent out a partial parts list, I wanted to document what I have built so far. After looking at multiple programs to enter a schematic and perhaps design a PCB, I settled on a web browser based system called EasyEDA. I felt it was easy to learn, had a good number of components in the library, and had good capability for designing custom components. I have not even tried the PCB design part so that will come later if I decide to do a printed circuit board.
Here is a image of the schematic and a link to a larger pdf file you can enlarge as you wish. This is a draft. Don't build anything from this as yet that is permanent. I cannot guarantee it until I thoroughly review. I think it is 95% accurate but don't hold me to that yet. I just wanted to show where I am now. I do not yet show the output for the function generator that gives the square and sine wave, just the connection for the modulator. Also, I do not have the input circuit for the "internal scope". I have a design with op-amps but still have to test that and write the code for that display.

http://louhaskell.com/data/generator/generator-schematic.pdf

Image

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Wed 22, 2017 10:30 pm 
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More progress today.
I finished the input op amp circuit that conditions the sweep signal into an analog input pin of the Arduino.
I had to level shift a negative signal up to a positive one and then I filtered out the AC signal with a simple RC low pass filter.
The code for the sweep on the LCD screen was not too difficult except that it had to be written to make it fast enough.
Hooked it all up and , by gosh, the darn thing worked. ;-) although in this photo it is off just a tweak.
I have the settings as you see - 455KHz center frequency, 40KHz bandwidth, sweep internal, rate 0 (max which is about 2 or 3 a second, and markers set to 5kHz from the center. Still a few nagging bugs to get out on special cases, but it basically works.
The big remainder of a question is - will it work on FM at 10.7 MHz ?? With all of these wires hanging all over on this prototype, I maybe doubt it. Needs cleaning up to avoid all kinds of bad parasitic capacitance.

Image

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Thu 23, 2017 2:28 am 
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Things are certainly moving along. Great job Lou!

Colin


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Fri 24, 2017 3:02 am 
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louhaskell wrote:
I think it is 95% accurate but don't hold me to that yet. I just wanted to show where I am now.

Without reading the whole thread, I'm guessing that the second DDS module there - the one labelled "sweep" - is the main signal generator, and has been modified so that its Rset connection is brought out on pin 14? That's not been made clear on the schematic.

(edit: Bypass caps - I see none. At a minimum I'd expect to see 100uF + 0.1uf ceramic on the input to the 3v regulator (switchmode?), and either 1uF ceramic or 1uF electro + 0.1uF ceramic on all the other modules & 0.1uF ceramic on the level shifter & DAC. It might be working now, but doing that will improve performance immensely for a buck's worth of bits.

Also, you're using the regulator on the Arduino Pro Mini to supply the 5v Vcc? It's only good for 150mA, and at 5v & 125MHz clock the 2 DDS modules alone will pull that at least. I'm guessing the LCD will pull another 70-100mA with backlight, and your output stage will probably pull something similar. You'll need an external regulator.)

louhaskell wrote:
I have also started to look at PCB suppliers. I am sure that the cost will be much smaller if multiple boards are made at once. If folks would want one, I could see about supplying those "for a small fee" ;-) I would use a protoboard unless the PCB could be less than $20 or so. If anyone has a great supplier, please chime in.

Personally I mostly use iTead, but for something like this any of the cheap Chinese board houses will be fine.

Even assuming all through-hole components & beginner layout skills, the whole thing will easily fit on a 10cm x 10cm board, & I bet any hobbyist half-experienced at board layout could do it on a lot less. US$20 will get you 10 double-sided, through-hole-plated, solder masked, & silkscreened 10cm x 10cm boards shipped from China.

Check out PCB Shopper for details.


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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Fri 24, 2017 10:05 pm 
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Rod:
Thanks for the comments. For sure, I agree with your view on bypass caps. I had planned on the usual 0.1 uF but I will take your suggestion for the 1uF which are only $0.22 at Mouser in quantities of 10. Will get a batch of them for sure. I had also added regulators for 5V and 3V as you noted in my latest version. I have run everything from my Uno board for now but that will not cut it as you also discovered with your math. So glad to have someone checking my numbers!
I appreciate that link and suggestions for PCB makers. That is a handy website for sure! I am using EasyEDA and like it. Good to see that their board prices are one of the best and they are highly rated on this website. I will get a number of boards and offer them up to others. If you or someone else outside the USA wants one, we will figure a way for non-USA based folk to order. If I get them and then ship them to Australia or Europe, it may be very expensive versus just ordering direct. Maybe I just email the Gerber file?
I am note experienced in this. Has been 15 years since I did a PCB.

I have designed the rest of the schematic and did my first board design, but it was crude so I dumped it. I will make note of the bypass caps and publish a new schematic shortly.
Then I will do a better board design.
I also moved to an Arduino Nano. I have not used the Nano because I could not get the USB port to work on my MAC to download the thing.
After much Googling, I found the proper code for OS X to make it work. And the fix is different on the very latest MacOS Sierra, so I had to find that one.
The Nano has the built in mini USB port for downloading, so when the bugs or added features come, it will be easy to update the software.
And it has 4 more pins available in the packaging for future growth.

I also am starting to think about a good way to design an enclosure. I think it best to mount the 5 BNC connectors directly on the PCB
and have them extend out of holes on the case. I had not planned to mount the LCD on the circuit board since that will enlarge the PCB a lot and make it more expensive.
Just planned a header for a flat cable to connect the LCD pins. And mount the LCD to the front panel with some small screws.
All ideas welcome, maybe even from some more experienced than me. The physical design aspect is definitely my weakest ability.

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Fri 24, 2017 10:51 pm 
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Well, I was just about complete with the update when I saw the note from our Aussie friend. Here is the schematic update including my new items as well as his good comments on more caps for bypass.
Next up another attempt at board design. I have updated all of the layout graphics for each component. EasyEDA had many library components but some I had to design myself. Was easy to do.
I also had committed to testing this beast on an FM radio. Since I gave my last FM radio to my son, I went ahead and bought a little Zenith H724 off eBay yesterday.
Got it cheap since the case is cracked, but I just wanted the chassis anyway and the cracked case made it cheap at only $15.

There is this photo plus the full PDF file is here:
http://louhaskell.com/data/generator/generator-schematic-v1.3.pdf


Image


(EDIT: Updated to V1.3 to fix several errors. March 26, 2017

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Sun 26, 2017 2:54 pm 
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Have been working on board design as well (and necessarily) as the enclosure and overall panel layout.
Here is a board design that has BNC connectors on the front panel. I made this board wider than necessary (7.8") to have ample spacing between the BNC connectors to allow for easy connection of cables. Perhaps I do not need this much as shown in the designs below.

Image

I have looked around and basically have seen 2 types of enclosure approaches. One has the BNC connectors on the front panel and the other has the BNCs on the side. See these examples. Not to scale!!

Image Image

The board design above would apply to the first example whereby the connectors are on the front panel just like many instruments we have all used .
Sort of the classic look. However, in looking around, I have seen many smaller instruments put the BNC connectors on the side, thus allowing for an overall smaller box, ease of cable location over the work space, and more real estate on the front panel for knobs and switches.
I am therefore now leaning toward this layout with the connectors on the side .

Would appreciate comments on this!

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 Post subject: Re: Microcontroller Based Signal Generator
PostPosted: Mar Mon 27, 2017 8:44 pm 
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As far as the location of the BNC connectors goes, I like the side-mounted arrangement, as it allows access to the front panel without cables getting in the way.

Colin


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