NBTV/SSTV-625 Up Converter MkIV

[acl]

Hi there,

Today I made a start on the control electronics. I'm using some fiberglass stripboard/veroboard purchased off Ebay. I prefer this to the paper based boards as it is more robust and the breaking of tracks easier. This batch has a white layer on the component side which gives it a nice pertina. Managed to get some genuine leaded solder as it is easier to work with and a new Antex soldering iron with a fine tip.In order to minimised stray capacitance the size of the board will be kept to minimum by using wirewrap cable on the coper side for most interwiring.

Regards Chris Lewis

[Steve Anderson]

Chris,

I'm a bit concerned you're not using disc-ceramic caps for the bypassing/decoupling. Those poly caps have a noticeable amount of self-inductance at some of the frequencies encountered here (e.g. 64MHz). I've updated the PDF (attached) to show which caps should be disc-ceramic. They also should be mounted directly on the pins/sockets of the chips on the underside.

There linear devices within the micros, it's not all digital, comparators for example which we will be using. Keeping linear devices stable at these speeds is essential. As many can attest, logic devices also can suffer from the affliction. In a production environment they would be SMD chip caps, and along with other components can be on either side of the board. Double-sided in the truest sense!

To keep things compact mount resistors vertically, not as pretty maybe, but the Japanese have been doing it for decades and it works.

I also note (as yet) there's no header for programming the micro(s) with the PicKit 3.

Steve A.

SSTV-625 MkIV Main 1 v4.pdf

(466.58 KiB) Downloaded 275 times

C-DISC-AEC-P5.jpg (8.2 KiB) Viewed 7497 times

[acl]

Hi Steve all noted. I have ordered some disc ceramics now. The reason I haven't included the provision for on-board programming is that the PIC3 programmer came with it's own ZIF programming adapter.

[Steve Anderson]

Yes, but if there's software update later on it means pulling out the chip(s) and putting them back in - best to keep that to a minimum. For volume production a ZIF socket should be used. With a header on board you program the device, verify the programming and run the program without removing the PicKit 3. It 'disconnects' once its task is over.

Interesting to note that the Microchip version only comes with the programmer, a USB cable and a CD ROM (which is usually out of date), and a quick-start guide. Yes, I've bought a few over the years.

When this one rolls over and puts its legs in the air, it's be a PicKit 4 next which handles 16 & 32-bit devices better, and still the 8-bit devices too of course...and amazingly the PicKit 4 is slightly cheaper!

Steve A.

[acl]

Board to date

Hi Steve,

More progress today, mounted all components on board. Work remaining reduce inter track capacitance by breaking tracks as near to active circuitry. Check build, connect disc ceramic capacitors across each individual chip and where outlined on schematic. Wire wrapping cable to be used to wire between devices on the copper side keeping cables as shot as possible.

[Steve Anderson]

I've yet to make a start on my build, gotta clear the junk off my workbench from the last (non-NBTV/SSTV) project, and I'm still in the process of documenting it. So it may be 3-4 days before I get going. I also still need to do a small amount of ordering supplies...delivery about the same timescale.

Steve A.

Chris, can you provide the link to the E-bay supplier you used for the stripboard? Is it tinned on the reverse? It's slightly smaller than the similar sized version I can get here, but here it's untinned, and it tarnishes after a while, making changes/modifications difficult after some while.

[acl]

Stripboard

stripboard.JPG (37.67 KiB) Viewed 7473 times

https://www.ebay.co.uk/itm/2pcs-100x160mm-Stripboard-Prototyping-Fibreglass-uncut-joint-pcb-breadboard-vero/223962367689?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

This is some of the best stripbpard to work with. Tracks easily broken. Nicely wrapped in cling film to reduce tarnishing after period. If delivery is too long I can post you some from the UK.Yes it is beautifully tinned easy to solder.

Regards Chris

[acl]

Read Panel

Latest build

Todays work. Mechanically assembled all components in to housing and tested power supply. Outstanding work to check control board carefully and bus wire power supplies and interconnections between devices and add ceramic capacitors where shown.

[acl]

I found out how to connect up the PICKIT3 Programmer to the ZIF board. I did think of redoing the board and including the programming pins. Perhaps if we go down the PCB route if there is enough interest shown we may include this.

[acl]

5 volt and zero busses wired

'Eyelets' to support cable wiring

Circuitry checked against schematic diagram. Unused tracks cut back to reduce ‘pick-up’ and ‘eyelets’ made up of tinned coper wire soldered one end used to support the hard-wired cabling power supply busses and inter-chip wiring and suppression capcitors Board to be cleaned and checked for any bridges. Kevlar wire-wrapping wire used to connect up;

[Steve Anderson]

A few minor updates, error corrections identified. Not worth posting circuit again at this stage. Text should do it...

IC102,21,RB0 goes to the base of TR201, (Connection 1E). A 'hangover' from when IC102 was a different device.

Also in that area VR202 should be 5K and R204 should be 3k3. It's one of those things 'that slipped through the cracks,' I've corrected the schematic now.

Steve A.

[Harry Dalek]

Is this the full unit the converter Steve ? i am trying to follow ,i can see you are still working on construction and Chris is building as well good job to i can see .
So i gather we will find out how well it works when one of you two gets it complete .

[Steve Anderson]

It will be in time, there a number of interim steps to do along the way starting with the output stage and its code, then working backwards...if the output stage isn't operational you ain't gonna see anything from the input side of things.

If you mean in terms of hardware, it is complete though the board won't have the switches, pots, LEDs, transformer and other stuff which would be mounted on/in the case. As ever, "It isn't over until the fat lady sings."

Steve A.

I'm also having headaches with ordering from my usual on-line supplier...just when you don't need it!

[Harry Dalek]

OK Steve there is interest out there on this and i did mean the hardware as in this is the device nothing extra apart from the power supply mentioned shown a while back ,so then i can see why Chris is building along side you .
Yes i suppose your programming is the key to the device i am very keen to see how it go's .
i have to learn a little more but i would expect to have a go at it when i can ,have to know what to order and do a big review of this .
Mainly the ic's would be needed i have lots of bits laying around ..does not look to bad soldering together of late use to CRT monitors can't be any harder than that .
Just got 2 new soldering stations which will make the hobby easier .

[Steve Anderson]

There is nothing significant in addition to what has been posted here before, though there are, and will be, updates as I get to grips with the device(s) and its/their coding. Although Chris is well ahead of me in the build I need to somehow circumvent the non-availability of some components from my local supplier. Mainly it seems their server is screwed as of this morning (11/01/21). Even an e-mail to them bounced back which is a rare occurrence these days. I'll leave it 24 hours and try again...

If there are others interested in this it would be nice to know who outside of Chris, perhaps Klaas, yourself (Harry). myself and maybe Chris Long ('viewing from a distance') and one or two others...

If anyone is a bit shy in posting openly on the forum, there is a means to negate that. Many fear that they'll be shot down by 'stupid questions' (there is no such thing), but if you are of that thinking, contact me privately directly here:-

E-mail GIF1.gif (2.46 KiB) Viewed 7427 times

A graphic to hopefully stop spam-bots...you'll need to enter this as text in your e-mail application in text as 'to', it's not a link..

There is also the PM (private message) button, but you do need to be a member here, but you don't have to post anything. Though in time you may be deleted as being 'inactive', but that takes a while...like months...

Unless you give permission nothing will be repeated here. This has happened before, so you'll not be the first for sure. I understand, for some, open forums like this one can seem a bit intimidating, but don't worry, start simple, privately, and off we go...

Steve A.