Flash and Joy - WIP

[dikdom]

Will you post to the UK? Certainly looks interesting!

Hope so, we'll see when we get there... (no rev3 boards made yet)

[dikdom]

You can see the cart in work here: https://youtu.be/62i6qcQ1nV8
(and my messy desk also, sorry for that).

I have some issues to solve, still. The switching PSU board doesn't seem a good choice right now. I'm getting familiarize myself with the original idea, the 1117-5.0 voltage regulator, but that would mean you need to have a 9V/800mA (or stronger) PSU. If I'm not mistaken, the stock PSU provides 700mA.

[Lardo Boffin]

The later ones came with a 1200mA PSU in order to support the printer but most of the issue ones I have seen came with the 700.

[1024MAK]

UK700 - 700mA PSU are rather common.
UK1200 - 1200mA PSU are surprisingly rare.

Although it’s quite pricey, one of the RECOM DC/DC converters, or the Traco Power equivalent, or even the MuRata versions.

Mark

[dikdom]

Although it’s quite pricey, one of the RECOM DC/DC converters, or the Traco Power equivalent, or even the MuRata versions.

Mark

well, ok. I thought about this one: https://www.hestore.hu/prod_10042763.html (hx1314g) and that is around 1.5EUR. But unfortunately it builds up the voltage too slow, probably because of the 100uF capactor at its output (and input) and the cart sometimes doesn't start on powerup. On reset there is no issue. I guess all the switching PSUs has some kind of delay on voltage build-up.
I didn't have such a problem with the 1117-5.0 or the 7805, but as the cart consumes around 220mA on its 5V rail (mainly because of the two GAL ICs), the stock 700mA PSU is not enough when using a linear voltage regulator.
I'm afraid this is going to be a limitation. (However the bigger PSU is not necessary if the original 7805 on the motherboard is already replaced with a modern, 7805 replacement brick you mentioned above)

[dikdom]

I'm measuring quite a contradicting currents...
So, originally I was using 1117-5.0 for creating the 5V out of the 9V rail. I measured the 9V current and it was 220mA. I didn't even check the output current, I took granted that it is the same.
Then I measured with an XC1314G based buck converted. It consumed ~80-100mA on the 9V rail (depending on SD card is inserted or not) and some more on 5V. This was the converter that turned on too slow, so sometimes the ZX81 didn't boot on power-cycle.
Then I measured a simple 7805CV (I guess). It used 140mA on the 9V (input) rail. This was the WTF moment. This 7805 was hot also after some time, but how come it consumes so much less than the 1117-5.0?? I have no idea. It turned on also instantly, so as a last resort a simple 7805 also could be used for the cart.
Anyway, I went on and aquired an MP-K78L05-500R3. This one also turns on instantly, consumes 90-100mA on 9V rail. It simply works. Much more expensive than a simple 7805 or a 1117 (like 3x-5x, but still under 5EUR), but it is not superhot, it fits with the powerconstraints of the stock PSU of the ZX81..

We are happy, Vincent.

[dikdom]

The batch of rev3 cards (20pcs) are ready. They work as expected: voltage regulator is cool (GAL chips runs warm/hot, but I think that is OK), green and yellow LEDs are just fine in luminance (reads flash chip, reads SD cards, expands ZX81 with 32kB RAM).
What doesn't look good on the data sheet is they don't work with ZX81+38 and TS1000/TS1500. Needs to be figured out why...
Otherwise I'm quite content with the result. I know that this cart is not the best, but I think its features are ok.

Anyway, most of these carts have their owners already. I plan to empty my desk first, then we can discuss the second batch - if there are enough (10+) ppl willing to order it... The price will be around 35-40EUR + package&shipment (from EU, Hungary).

Some photos:

and a video about the usage: https://youtu.be/78Akb6_0Los

And a close picture:

[Dim_75]

It looks great !

[1024MAK]

Excellent news

What doesn't look good on the data sheet is they don't work with ZX81+38 and TS1000/TS1500. Needs to be figured out why...

The TS1500 I can understand (it automatically detects if an external RAM pack is fitted and reconfigures it’s internal RAM). And IIRC the ROM code is slightly different.

But the TS1000 are almost exactly the same as a ZX81. Indeed, many TS1000 are built using an issue 3 ZX81 PCB. The main differences are:

• R30 is fitted to the TS1000 so that the ROM code can produce a NTSC 60Hz video output,
• The board has some extra components and the inside of the case is coated with a metallic coating, both to reduce the radio interference emissions,
• A 2k byte SRAM chip is fitted as standard,
• The case and keyboard are cosmetically obviously different.

The ZX81+38 is really a ZX81 compatible rather than a clone, so it obviously has a slight difference somewhere that is causing problems.

Please consider me as being interested if you do have more to sell.

Mark

[dikdom]

Mark,
PM sent.