KD2BD SSTV convertor

Forum for discussion of SSTV topics. Slow Scan television (SSTV) is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or colour.

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KD2BD SSTV convertor

Postby acl » Sat Sep 11, 2021 3:04 am

I have successfully built and tested John Magliacane's Triple PIC SSTV to 525 line convertor. I am extremely pleased with the performance and technical support from John. This is not a project for the beginner as there is a considerable fine construction work to perform. The writer build the convertor on two boards, the analogue filter and synch extraction was built on stripboard whilst the high speed digital circuits were built on 'blob board' to minimise track capacitance.
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KD2BD SSTV convertor

Postby acl » Sat Sep 11, 2021 3:18 am

IMG_3435.JPG

IMG_3436.JPG


Photos show the writers analogue board. This is the last time I am going to use fibreglass stripboard as it blunts the track isolation tool very quickly.
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Re: KD2BD SSTV convertor

Postby kd2bd » Sat Sep 11, 2021 5:04 am

Congratulations Chris, for being the first person to successfully duplicate my scan converter. :D

During the building and testing process, we discovered a few errors in my schematics that I have since corrected. The amended article describing the scan converter can be found here in PDF format.

It has been a while since I have been able to experiment any further with my improved (?) sync detection circuitry since I am heavily involved in caring for a parent who is suffering from dementia. Depending on how things go, I may want to add a fourth PIC to the design in place of the LM555 timer, which is a lesson for life: Never name your product a "6 Transistor Radio" when there is a chance you may need to add a seventh.

73 de John, KD2BD
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KD2BD SSTV convertor

Postby acl » Sat Sep 11, 2021 5:27 am

The analogue board construction was straight forward. Please note the pin assignments for the op-amps differ from John’s scheme as it made construction easier. The components were easily obtainable of eBay or, due to the demise of Maplin’s here in the UK I used a company http://www.bitsbox.co.uk to get the hard to find resistor values. The metalized Poly film capacitors were sourced from eBay and http://www.partcompany.co.uk . These capacitors are not used frequently here in the UK. The quad op-amps had to be sourced from China and after a time they appeared on my doorstep. Please note I am not affiliated to any of these suppliers. To eliminate problems during testing as there are many ‘chained’ filters each component was checked with a modern cheap LCR bridge readily available . Please see my original piece of test equipment.

IMG_3458.JPG
LCR bridge for home constructors

IMG_3461.JPG
Early 'Home brew' version
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KD2BD SSTV convertor

Postby acl » Sat Sep 11, 2021 6:20 am

The digital section of the convertor was the most challenging. My first attempt on stripboard worked although sporadic operation ensued tracked down to poor decoupling and layout. The mistake was me adding an IC socket where it wasn't required. Complete rebuild required.

IMG_3380.JPG
Original Digital board


IMG_3363.JPG
'rats nest' wiring reverse side of board
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KD2BD SSTV convertor

Postby acl » Sat Sep 11, 2021 6:39 am

Oh dear, poor layout and lack of decoupling.



IMG_3423.JPG
Vertical lines superimposed on picture initially thought to be RAM problem.


pic_273_1.bmp
Video output of start up screen
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KD2BD SSTV convertor

Postby acl » Sat Sep 11, 2021 7:05 am

Took advice from John with regards layout of digital board.

digital_board.jpg
Johns layout
digital_board.jpg (100.19 KiB) Viewed 9594 times


Copied with the exception of keeping all three PICs on the digital board.

IMG_3437.JPG
Rebuilt digital board


IMG_3439.JPG
slightly neater


To optimise data bus wiring the eight bus lines were soldered directly to the IC pins on the component side of the board.
IMG_3441.JPG
Data bus wiring added
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Re: KD2BD SSTV convertor

Postby Steve Anderson » Sat Sep 11, 2021 12:46 pm

kd2bd wrote:Never name your product a "6 Transistor Radio" when there is a chance you may need to add a seventh.

Well, how about "The Triple Pic Plus"? Covers multiple 'sins'. As you've seen I just tend to give further iterations simply a version number, v1, v2, v3 etc.. much the same as software versions. Maybe not as descriptive, but it generally seems to work.

...which prompts me...I must get back to my stalled update on my first version. In the light of the current chip shortage it may be a case of starting from square one again. As the display is now a VGA monitor the speed requirement has effectively doubled, and that's creating a few hurdles as well...once I get clear of stuff currently on my plate I'll get back on the case...

Thanks for your updated version too John.

acl wrote:Oh dear, poor layout and lack of decoupling.

I know I go on and on about this all the time, but putting a 'positive spin' on the matter that's an example of why I do keep repeating myself. Aside from the demodulator and power supply I squeezed the MkI onto a single board, yet still added where possible plenty of fat grounds (green lines/tracks) and lots of decoupling capacitors. This will be doubly important (literally) in the VGA output version.

SSTV-625 Board Layout 1-Model.gif


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Re: KD2BD SSTV convertor

Postby Steve Anderson » Sat Sep 11, 2021 2:50 pm

Although my last post regarding the SSTV-VGA up-convertor was in mid-March, some work has been done on it since. Looking ahead, possibly I'll resume effort on it prior to the end of this month (September).

Steve A.

One factor that has now forced me into going the VGA route is we don't have a TV/monitor in the house that has a 625/525 analogue input anymore. All PC, VGA etc. or HDMI. Though I checked the newest addition can still display a 800x600/60Hz VGA analogue signal before purchase, even so, there are others here that definitely can.
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Re: KD2BD SSTV convertor

Postby Harry Dalek » Sat Sep 11, 2021 5:06 pm

Great work Chris ! you got there ,and not a bad picture very classic 70's look to me !
Impressive job indeed !
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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KD2BD SSTV convertor

Postby acl » Sat Sep 11, 2021 7:59 pm

Thanks Harold
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KD2BD SSTV convertor possible PCB design

Postby acl » Sat Sep 11, 2021 8:02 pm

With regard to construction of the CPU section I thought I would allow other interested parties to build one of these excellent convertors without requiring the dexterity of a neurosurgeon using an electron beam microscope to solder wires to the IC legs. I spent some time toying with designing a PCB and using ExpressPCB designed the board as per picture below. Please note this has not been fully checked but has been shown in order to stimulate interest. If anybody feels like improving on it or making a more professional board constructive criticism is welcome. It is my second board design so it is a long learning curve. Please note It is envisaged to add ground plane.
I did try Eagle but has trouble loading discreet components libraries as it mainly catered for surface mount devices. I know the boards are cheaper and there is an auto router to tidy things up. Anyway, the main limitations of my design are the size of the board, inability to produce curved track edges to reduce EMC emissions and the UPS cost of delivery to the UK from the States. However, Gerber files are available to allow future batches to be produces in the Far East at a reduced price.

Capture.JPG
Idea for PCB for CPU section
Last edited by acl on Sun Sep 12, 2021 12:03 am, edited 1 time in total.
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KD2BD SSTV convertor digital board construction

Postby acl » Sat Sep 11, 2021 11:59 pm

We now turn our attention to the digital board. Due to the high frequency signals ‘flying around’ we need to be careful about minimising bus wiring length and decoupling of power supply connections to the active devices. In the real world If we were to produce this on a PCB there are rules set out to keep address and data bus lines the same length to prevent ‘standing waves’ being set up and causing malfunction and physical arrangement for bus systems.

https://www.expresspcb.com/tips-for-designing-pcbs/

However, if we are careful with the layout, we can reduce chances of failure.

For the digital section I used what I call ‘blob board’ recommended by John. It comprises of a series of copper pads rather than strips on a board which we can fit our components. All my components were sourced on eBay and presented no availability problems. Luckily the surface mounted OPA2365 dual op amp used for the final video output signal was already mounded on a PCB allowing connection to a standard 8 pin DIL header. On my system I omitted U8 and all serial interface components as I felt I would not be utilising them.
Turned pin sockets were used extensively on both boards due to their reliability especially when changing chips. Once all sockets were mounted and a few discreet components I was now ready to take on the task of wiring up the circuitry. To do this I used single strand 30SWG wire wrapping wire. The sleeving is made of a type of Kevlar which is fairly soldering iron proof due to the close proximity of the connections. The cable is stripped using a special tool so as not to ‘nick’ the conductor and cause a cable break. Stripping and twisting bare ends before tinning and soldering to the components was a fairly easy task.

IMG_3463.JPG
Stripping tool
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Compatability

Postby acl » Sun Sep 12, 2021 6:35 am

Hi there Steve,

At present Johns converter is as steady as a rock on both my CRT monitors as is my USA purchased Robot 400. However none of the LCD monitors will 'bend' to suit 525 lines. I did invest 7 GBP including postage and packing from China for a NTSC to PAL converter as shown below but it didn't seem to work with a monochrome signal.


Regards Chris

s-l1600.jpg
PAL to NTSC and visa versa unit
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KD2BD SSTV converter

Postby acl » Sun Sep 12, 2021 6:42 am

Much improved video output signal due to John's suggested layout of digital board.

pic_294_1.bmp
Start up video output signal
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