derkom's doings

[derkom]

I have enough little projects (and some not so little) going on that I figure I might as well belatedly start my own thread in which to ramble on about miscellaneous accomplishments, disaccomplishments, and excessive flux consumption. I have ended up with quite a bit of old hardware over the years, much of it Atari, much of it not, and as I am getting more confident and qualified, thanks in no small part to the H4 and all of the great assistance I've got from other members here, I find myself pulling a lot of it out and tinkering with it, with occasional reportable success. So I will endeavour to post some of the more interesting updates here, for others to enjoy, gently mock, or ignore, as they see fit. :P

[derkom]

First, a question related to something I asked in @Smonson's HDMI/DVI thread: Does anyone know of any (preferably affordable) hardware that can accept a HDMI/DVI input, scale it somewhat arbitrarily, and output it again? By "scale it arbitrarily" I mean that for instance I would like to take the output from the upcoming HDMI board, at something like 720x400 or 800x480 and then produce an output at the native resolution of an LCD panel (1366x768 or even 1920x1080), but I do not want the input necessarily filling the entire output. I'd like to be able size and position the input within the output.

I'd like to find a turnkey solution for this, and so far I've been coming up empty. I'm sure there's some pro hardware out there that can do it, but that's not likely to be within my budget. I'm not entirely opposed to finding an IC that can do this and working up my own board design, but if something out there can already do this, it would make things easier for someone without a lot of design experience.

[derkom]

I've had a broken Sodastream Power machine stuffed in a closet for a couple of years. It naturally quit working right out of warranty, flashing all the LEDs whenever powered up. I looked into the problem back when it broke, and it seems the flashing LEDs are just this device's catchall error code, and it was apparent that none of the supposed fixes offered online would fix mine. It seemed the logic board was just dead. So I stuck it in a closet and ignored it.

I finally decided to pull it apart again and have another go at fixing it. Studying the mechanism, it was clear the entire the entire device functions from just one servo that pulls down on an actuator to release CO2 into the water. Someone online mentioned the servo going bad on his, but I didn't think this was my problem, since I was getting the error indicator without even asking the machine to do anything. But I figured I might as well test the servo, so I pulled it out and hooked it up to an Arduino Uno and poked at it a bit, and the servo was clearly fine.

Well, if the servo works, the mechanism works (I can pull on the actuator by hand and release CO2), and I can program the servo from an Arduino, what's stopping me from replacing their logic board with my own? The answer is nothing!

So I swapped out the Arduino for a NodeMCU V3, and threw together a board duplicating the function of theirs (three buttons to activate the three different carbonation levels):

IMG_20200425_082206.jpg

Through trial and error I figured out the angles to request from the servo for off, CO2, and rest, and I downloaded some videos from YouTube of people using their own machines, overlaid a frame counter with ffmpeg, and then figured out all the timings for the three modes. And it worked!

Not wanting to lose the function of the original buttons and LEDs, I butchered the original logic board enough to electrically isolate them and then soldered in a bunch of my own wires like some kind of facehugger:

IMG_20200425_221718.jpg

Then rebuilt my breadboard prototype on a perfboard:

IMG_20200426_193124.jpg

Installed the whole mess back into the machine (better mounting solution in progress):

IMG_20200426_230829.jpg

And fixed!

Screenshot_20200427-161844_Gallery.png

Saved from the rubbish heap. :dualthumbup:

[exxos]

:bravo:

And today's geek point is awarded to.... :2k2:

[stephen_usher]

Actually, I think it warrants an over engineering award... Actually, surely that should go the company who makes the Sodastream, is it still Kenwood?

What was so wrong with pressing your thumb on a button on the top, as we did in the 1970s? :lol:

[derkom]

What was so wrong with pressing your thumb on a button on the top, as we did in the 1970s? :lol:

I used to have one of those. Got the Power version when the manual one eventually broke. And then the Power broke, too. I didn't buy a third one. But give me too much time at home with a soldering iron, and something's bound to happen. :D

[derkom]

A couple of years ago, a friend of mine who processes a lot of surplus hardware (and feeds various oddities my direction) gave me a Mindset M1001, an 80186 nominally PC compatible computer that I understand was designed by some of the same engineers who built the Atari 400/800. He had not powered it on, and the box ended up in the attic.

IMG_20200513_200129.jpg

A couple of days ago, I finally pulled it back out, opened it up and discovered the PSU is shot, transformer dead. So I pulled out a Meanwell RD-50A, built a little inverter board to produce the -12V rail the Mindset wants, and connected it up via the original power connector from the dead PSU.

IMG_20200513_140910.jpg

Plugged it in, flipped the power switch on the keyboard, heard the power relay click inside the main unit, and then .... Hey what's that smell? Oh no, the magic smoke has been released from the keyboard! :fire: Quickly pulled the plug and went to investigate. Inside the keyboard I found this:

IMG_20200510_181614.jpg

Eek! Fortunately I was able to determine from others' photographs that these used to be 51 Ω resistors, so I could replace them, but no point in doing that without finding the fault. The resistors in the keyboard are just the weakest link, and likely the old PSU used to be the weakest link, and that is why it's dead.

Fortunately, since this is just the power relay circuit, there wasn't much to investigate, and it didn't take me too long to find a 1N4148 right next to the power relay on the main board that was showing 1 Ω resistance in both directions, and which would create a 12V dead short through those resistors when the relay was turned on. I had some extra 1N4148s left over from the H4 project, so that was a quick replacement, and despite the PCB in the keyboard being somewhat burnt, it was still electrically fine, so the 51 Ω resistors there were a simple replacement as well.

Plug it in again, flip the switch again, ...

IMG_20200513_160122.jpg

:excited:

It works! It came with a few floppies and seems to boot MS-DOS 2.0 just fine. So now I will find some space somewhere to finish setting it up.

[rubber_jonnie]

Interesting to see that, I did see a review of the Mindset on YouTube, the 8Bit Guy I think.

Only the second machine I've encountered using an 80186, the other being one from RM, who I later ended up working for as a field service engineer.

Do you have any detail on the inverter board at all please, I'm a fan of Meanwell PSUs and it may be useful in the future.

Thanks.

[derkom]

Do you have any detail on the inverter board at all please, I'm a fan of Meanwell PSUs and it may be useful in the future.

Sure. (Caveat: I'm fairly novice at building electronics from scratch, so no guarantees this is the best approach to the problem. Suggestions from others welcome!)

I checked availability at a local electronics supplier and found they had some Analog Devices LT1054CN8 Switched-Capacitor Voltage Converter with Regulator ICs for around 5€. This IC has numerous applications, including voltage inversion. I built the inverter following precisely the schematic found on page 10 of the datasheet, and using tantalum caps as recommended. I decided to go the unregulated route because it's simpler and because the -12V load from the Mindset is quite small (details are in the service manual), so regulation isn't a requirement. If I were building this for a system where there was some real load on the negative rail, I would build the regulated version.

Here's a couple of better pictures of the board, although the schematic in the datasheet really says it all. Sorry the focus is a bit garbage on the second one. Didn't realise that until now, and I'm not going to dig back into the system to take another photo. :D

IMG_20200513_132156.jpg

IMG_20200513_132224.jpg

That board seems to work just fine, taking +12V input and producing around -11.9V output under moderate load.

If anyone ends up building one of these, do note that the capacitor on the output is reversed from what you might expect, with the positive terminal connected to ground.

[rubber_jonnie]

@derkom That's great, thanks very much.

I'm also a novice too, but getting there slowly, I'll see about building one and seeing what happens :)

Hopefully no magic smoke!