USB Floppy Emulator for CPC664

[RWAP]

Someone on Facebook has proven that Zaxon's USB Floppy Emulator for the CPC6128 works with the CPC664 which is great news.

See the review at The Amstrad CPC 6128 USB Floppy Emulator Hardware BIG Review

Unfortunately, the board needs a bit of a minor redesign as the fit is not too good due to the height of the 664.

Zaxon says he needs at least 20 people to be interested - the price will be approx £8 more than the existing CPC6128 version - would there be enough interest?

[Bryce]

How about he answers all the questions he was sent about his last piece of hardware before we give him answers to new hardware.

It's not acceptable to keep popping up with questions to make money for himself, but ignore all questions from people who spent money on his last attempt. The whole concept of community hardware lives from the fact that you can directly contact the creator and ask questions / give feedback. He doesn't seem to have understood this.

And why is he getting you to ask this question? Is he afraid to show his face here?

Bryce.

[RWAP]

I asked because I didn't know he was registered on here, until earlier today.  Having arranged for replacement membranes for the CPC664 it would be nice to be able to see more of a market for that machine.

What questions are you on about?  I administer sellmyretro and so far as I can see he has always responded to questions from purchasers and potential purchasers in a timely fashion.

I found a long thread on here which (without reading through all of the pages) seems mainly to be complaints that he had tracked down some original Amstrad chips and decided to use them for his own projects rather than offering the chips on their own, but that seemed about it.  Zaxon has told me that the response from certain parts of this community has indeed put him off taking part in the discussions on the site - although I don't think he appreciates that translation does not always help here and so sometimes people's comments can come across in the wrong context.

Maybe a list of questions would be the best way forward

[Bryce]

Zaxon is a member here, his username is Piotr. I have sent him many PMs, e-mails and posted questions here in threads, and I'm not the only one. He answers questions up to the point that you order something, but as soon as he has your money he never answers again. So, let's test it again a last time. These 20 sample questions are to Zaxon/Piotr: All questions are in relation to the JustCPC Board:

1 - Why have you used a 2.6A inductor on a 3A regulator. In the case of a short circuit the inductor will burn before the regulators safety mechanisms take effect?

2 - Why have you left no possibility to heatsink the regulator, as it is, the regulator will go into thermal shutdown at around 1A, yet you claim it can supply 2.6A? Not a chance!

3 - Why have you left floating pins on the PCB, this can and will cause instability?

4 - What is pin 1 of the 40025 ROM connected to?

5 - Why have you spaced the resistors so closely that even 1/8W resistors won't fit in certain places?

6 - Have you even checked whether 1/8W is enough in all cases?

7 - Why have you chosen a non-standard connector to the monitor and left 2 pins empty that could have carried the sound signals?

8 - What does J6 do?

9 - What does J7 do?

10 - Why have you chosen a data seperator that was never used on the CPC although the originals are easier to source than the one you chose?

11 - Why bother putting an edge connector on the board when the cut-out is too small to take original expansions and even if they did fit, they would block other ports that you placed too near the expansion port?

12 - Why does a non-populated floppy section cause the CPC not to boot. This doesn't happen on a real CPC?

13 - Why have you not mentioned that the bridge rectifier will overheat and needs a heatsink?

14 - What does the bodge resistor under the PCB do and is it required on all versions of the board?

15 - Why have you made the footprint of the buck diode so small that the diode needs to be stressed to get it to fit?

16 - What does R9 and R10 do and why are they optional?

17 - Can I use an AY-3-8912A on this PCB or does it need to be a non-A type?

18 - What are the second two pins on the floppy power connector connected to?

19 - Does the PCB have any internal ground plane?

20 - Why did you bother using shielded sockets and then not bother connecting these to ground?

So, that's just the start. I know that I can easily work out the answer to many of these myself, but not all questions came from me. The point is that I and others have asked all of these and not a single answer has come back, yet when he's looking to cash in on his next questionable project he's suddenly available to answer e-mails within minutes.

So Zaxon/Piotr: If you are serious about building and selling retro hardware, then support it like you should and stop hiding behind your keyboard. You took our money, now take our questions!

Bryce.

[RWAP]

I have passed the list onto Piotr (Zaxon) - although I am not sure what you mean by number 12 !! Do you mean an unformatted sector on a floppy disk ?

My guess is that some of these issues may relate to differences in manufacturers for some of the parts - specifically when you talk about physical connections

[Bryce]

No, if I remove the ICs from the floppy section (all ICs to the right of the RAM) the CPC doesn't boot. It should. A real CPC does. This means he has either used a gate there for something that the CPC needs or it's due to instability.

You don't need to pass the questions on. He's logged in here right now, he just has his status hidden and I'm sure he's reading this as I type.

Bryce. 

[Piotr]

Bryce, it is amateur board so can be not perfect, sorry, i try do my best, here is answer for yours questions:

1. Becouse i use it also in JS128, cheaper to buy bulk
2. Hmm, maybe my fault but i test boarw with 72 hours stress test and all was ok
3. What pins?
4. My fault is not connected
5. My resistors fits. 1/4wat subminiature.
6.yes i check for subminiature resistors
7. Becouse i use this socket also in JustSpeccy 128 and i can use one cable for both machines, on this 2 pins is audio out in Just CPC.  Again, save for components ordering.
8. J6 is stereo out for jack , easy to check via multimeter...
9. J7 is +5volt and GND for future mouse interface
10 . Becouse i made and use it in  DDI too , and again easier and cheaper to order.
11. My mistake
12. Sorry , board boot without floppy section, do you fit R21?
13. 72 hours stress test and working, i think is obvious if is too hot add radiator?
14. Is not required with orginal HAL chip,
15. For mi is not to small, i fit diode without problem.
16. r9 and r 10 is not optional, is 680 r and must be fitted
17. No, you can't
18. Is not connected
19, No
20 . My fault

[RWAP]

I can see why no.16 caused a query - on your page for the justcpc parts, you have stated "Mainboard section
(r9 and r10 680R, optional,do not fit)"

As for no.11 - this is truly unfortunate - presumably you could offer a short adaptor board to extend the slot?

[RWAP]

By the way - surely it would make more sense for a moderator to split this topic, so that the third post onwards appears in a thread about JustCPC questions on their own - it is not really linked to the USB Floppy emulator for the 664!

[Bryce]

Firstly, thank you for finally answering the queries we have. It's just rather unfortunate that you ignored all these questions for so long. It didn't do your reputation any favours. I (and others) could see how often you were online and you chose this long not to answer the queries.
I can understand that it is an amateur board, but you really need to spend some more time learning electronic theory before you release stuff like this. There are many people here, including myself, that would happily help you. Most of my questions were just queries about design decisions that I didn't think were good, however, the power section of the JustCPC really is a mess. So here's a few tips for the next version:
- The LM2596 can only supply up to 1A in the configuration that you've made (without heatsink). However that's the absolute limit, the core (die) at 1A will already be at over 100°C and the LM is likely to have a very short life. I measured almost 70°C on the surface of the part on my board. A simple "pour" (extending the copper under the part) or leaving space for a heatsink would have removed this problem with no extra cost.
- The inductor (and all other passive parts) in a switchmode supply should always be able to take more current than the switching controller. The controller has the intelligence to switch off, inductors don't.
I know you say you did "stress tests", but in electronics you do the maths first, using the numbers from the datasheet. The stress test might run stable for 72 hours, but that doesn't prove that the parts won't fail in a month, the maths will. If you had spent a few minutes reading the LM datasheet, I am sure your design would look very different.

As far as the bridge rectifier is concerned, I actually installed a 6A part on my board and it still reaches 56°C after about 10 minutes. It won't last long either. The datsheet told me this anyway. My plan is to convert the PCB back to 5V CPC PSU input.

Regarding the footprints. On DIY projects where you don't supply the components, you should assume the user will install the parts most easily available, so making a board for extremely difficult to find sub-miniature parts is a bad idea. And regarding Q15: The diode in the photo of your board is stressed, the pins of this diode shouldn't have a 90° bend directly at the case, they should make a natural curve, ie: the holes should be at least 14mm apart.

Regarding the floating pins. Pin 1 on the ROM is the only one I am 100% sure of, because you confirmed it here, but I remember finding others. No input pins of any IC should ever be left unconnected. They act as tiny antennas and can cause oscillations that can cause chaos in a circuit. ALWAYS strap all un-used inputs to GND or 5V.

RWAP has already answered the R9/R10 question: You also need to update the instruction page and explain what these are for, also what the header pinouts are and what the bodge resistor is for.

I'll leave it there for now, with the request that you really should give more respect to the people who buy your hardware. Luckily I have the equipment and knowledge to have worked out the answers for myself and the price didn't break the bank for me, but others may have saved to buy your hardware and without your support they may be left with an expensive paper-weight. Support is what makes us different from the Chinese factories that churn out junk electronics.

Bryce.

[Gryzor]

I love the fact that this is well-documented, well-intended and in-depth, honest feedback. Thanks.

[ZbyniuR]

Is anyone working on to floppy emulator could use .DSK instead .HFE?

[RWAP]

The problem with that is that it would require a re-write of the HxC firmware used by these floppy emulators.

[Bryce]

It's possible, but it would ONLY be able to read DSK, nothing else. The reason why Jeff uses HFE is because he can convert any format to HFE on the PC, so then the µP only has to know one format. There's not enough room in the µP he uses for more than one format. You'd have to use a much bigger and more expensive PIC to do that. The µP would also need to recognise the format automatically which may prove very complicated.

Bryce.