MotherX4 Alternative for CPC 464 Users

[TotO]

I was able to see your MotherX4 clone boards (4 and 1 connectors) and I'm surprise about the lack of +5V large track and ground plane to power the expansions. Instead, they use the same thin tracks than other signals... Really weak. Hope for users that was fixed since?

[LambdaMikel]

I was able to see your MotherX4 clone boards (4 and 1 connectors) and I'm surprise about the lack of +5V large track and ground plane to power the expansions. Instead, they use the same thin tracks than other signals... Really weak. Hope for users that was fixed since?

Nobody ever reported any problem with it - I believe that is because I do not have a voltage dropping diode on board  So the voltage comes out ~ 4.8 V for most cards in the end if you have a reasonable CPC power supply.

External PSU "extra" expansion board PSU should not be necessary at all. Unlike other backplanes I can power the DDI3 without any extra PSU or board modification.

It's actually not at all a MotherX4 clone... that design was inspired by the old "Dat Becker CPC Hardware Erweiterungen" book - see page 80 / 87 here

http://www.cpcwiki.eu/imgs/4/40/CPC_Hardware-Erweiterungen.pdf
I guess you guys didn't have that in France and needed to "reinvent" it 

But yes, I have made a 2nd revision with wider tracks. I am not sure which one you have.

[TotO]

Nobody ever reported any problem with it - I believe that is because I do not have a voltage dropping diode on board  So the voltage comes out ~ 4.8 V for most cards in the end if you have a reasonable CPC power supply.

Poor design and stupid answer to justify it... Think to users... 

[LambdaMikel]

Poor design and stupid answer to justify it... Think to users... 

Well you should only put things on board that are needed... not extra crap. IMHO.

Please read the whole answer first.

[TotO]

Well you should only put things on board that are needed... not extra crap. IMHO.

Your board use really too thin tracks for VCC and GND. I report that, because it is weak compared to the CPC mainboard design and using many expansions can cause problems to users. Here the problem.

So, please, don't change the subject about the original MotherX4 board design, because it is more clever than your clone craps.

[LambdaMikel]

Your board use really too thin tracks for VCC and GND. I report that, because it is weak compared to the CPC mainboard design and using many expansions can cause problems to users. Here the problem.

So, please, don't change the subject about the original MotherX4 board design, because it is more clever than your clone craps. 

OK, you win 

To base this discussion a little bit more on evidence, I can measure and post the voltages at the end of the different CPC backplane (including crap) solutions we have, with and without load (2 or 3 cards being plugged in I mean).

The reason and rationale for LambdaBoard was NOT to create a "crap clone of MotherX4", but to have an edge connector at the end.

And, as stated before, it is more a "clone" of this 80s book CPC backplane extension if anything, see Page 80 / Page 86:

http://www.cpcwiki.eu/imgs/4/40/CPC_Hardware-Erweiterungen.pdf


Anyhow. If anybody has a problem with it, please return it to me or grab the open source design of the LambdaBoard and improve it to fit your needs.

Have a good weekend.

[TotO]

Page 81 of the linked book, the tracks are at less two times wider than yours. Look the GND rails width on both sides! 

It is your design, I will not fix it because you put open source to not have to deal with problems. Think noob users, you are not Piotr and I'm sure that you will give a nice support if peoples encounter issues. The goal was just to know if the design was updated since (error is human).

[LambdaMikel]

OK, appreciate the input, but 3 more things

   
• CPC has 2 GND lines already (2 and 49), both are connected... so that also doubles the width already. My extensions are also always connecting to both GND tracks.
• VCC would be nice to be thicker, agreed!
• GND backplane copper makes soldering so much more difficult, because of heat dissipation... especially for a card with so many solder points.

I can rework the design at some point. But I would really prefer to only do that if somebody has an issue with it, so it would be based on some need... so far I don't see the need for that. But I will do what you suggested at some point. Thanks for the input! But mainly because I don't want to be perceived as beging stubborn, not because I see a need for that. I just dislike dogmatic doctrines "you have to do this or that" when there is not a lot of evidence in support for that.

Another thing that would be useful is to add the key lock gap, as suggested before, but a lot of work to cut it out manually. Not sure the PCB manufacturer will be able to do this.

It is your design, I will not fix it because you put open source to not have to deal with problems.

Hmm, not so sure that this was my intent when I put it open source... anyhow.

As always, it is a balancing act to find a good compromise between GOOD ENOUGH and OVER ENGINEERED design. And a design is never finished - there will be more iterations to come.

[TotO]

Hmm, not so sure that this was my intent when I put it open source... anyhow.

I'm sure, but it is sadly a recurent answer when someone ask for an update to a wiki or open source project -> DIY.

Here an alternative design based on the first version of the board (CTC-AY) : MotherX4_V2.1.zip

[LambdaMikel]

I'm sure, but it is sadly a recurent answer when someone ask for an update to a wiki or open source project -> DIY.

Here an alternative design based on the first version of the board (CTC-AY) : MotherX4_V2.1.zip

Thats great - now, if I ask you to PLEASE ADD AN EDGE CONNECTOR to it, will you do it? Ore are you asking me to DIY 

[TotO]

Thats great - now, if I ask you to PLEASE ADD AN EDGE CONNECTOR to it, will you do it? Ore are you asking me to DIY 

There is already an edge adapter to plug on the passthrough pins, to be at the right height for the original interfaces. 

[LambdaMikel]

There is already an edge adapter to plug on the passthrough pins, to be at the right height for the original interfaces. 

And would it not be better to have that directly on the PCB, such that no bad connection from PIN to SOCKET contact only connection (and resulting voltage drop etc.) will occur? (Upps, that might be a rhetorical / suggestive question)

[TotO]

The goal was to make something versatile for the different types of CPC mainboards (Edge, Centronics) and usages. Sure, putting directly the edge save a lot of soldering work, but that means the users have to raise the MotherX4 PCB too.

[LambdaMikel]

The goal was to make something versatile for the different types of CPC mainboards (Edge, Centronics) and usages. Sure, putting directly the edge save a lot of soldering work, but that means the users have to raise the MotherX4 PCB too.

See, that's a good point... every design is some compromise. For some anticipated most likely use case.
Now, I already tried that solution, and wasn't satisfied with it because it is very wanky. See picture attached. Also, that only worked because I removed the diode. I like to stress that everything I am saying is based on evidence and hard facts, not on dogma or "has to be".

[TotO]

The DDI-3 is heavy and not sat on the table... The official expansions does.

Here, you are using an edge adapter as well and some other peoples will put instead:
- MX4 to Edge ribbon
- MX4 to Centronics ribbon
- MX4 to MX4 ribbon
- MX4 to whatever ribbon

[LambdaMikel]

The DDI-3 is heavy and not sat on the table... The official expansions does.

Good. In general, I suggest to reduce the number of pin to socket contacts if possible though, because that's the weakest point. The width of VCC and GND tracks doesn't matter at all (we only have ONE VCC pin!) IF the IDC socket connection is wanky or loose.

[TotO]

I agree that is always better to not cumulate too much the connections.

[LambdaMikel]

https://oshpark.com/shared_projects/gfReKSs4

[LambdaMikel]

Here an alternative design based on the first version of the board (CTC-AY) : MotherX4_V2.1.zip

Is that a DIODE on the PCB there? If so, it better be optional...

[robcfg]

Probably as optional as the security belt on a car...


If everything goes right, there's no difference, but the day something happens you wish you had it.

[LambdaMikel]

Probably as optional as the security belt on a car...
If everything goes right, there's no difference, but the day something happens you wish you had it.

@robcfg
I guess you don't know, but in the previous version it dropped the VCC so much that DDI3 would not work reliably at the end and the display was so dimm that it was unreadable... many people ended up removing it (the diode, not the DDI3).
So yes, there was a big difference.

http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/mother-x4-and-ddi3-mods/msg162630/#msg162630
Adding an extra PSU should not be necessary for 90 % of all CPC expansions (unless you have 10 or more or something crazy like that).

[TotO]

Well... Do you know about steering diode usages? Your board does nothing more than a SCSI ribbon cable.

When the MotherX4 was built in 2013, I have spoke with some electronicial peoples and they recommanded to add it.
First, because it is better than nothing to protect the CPC... Next, because one compensate the other if it goes weak, instead of failling.
Some peoples use the external PSU to save the content of a RAM Drive, can turn off the CPC power without disturbing the expansions...

In fact, the problem is for your kind of "arduino" modules that require to be 3V3 powered and your 5V to 3V3 regulator should not have enough voltage from the CPC itself.
The DDI-3 was never intended to be plugged at the end of the MotherX4 without an adapted external power supply... But directly on the CPC464 edge connector.
Need more voltage? Input more voltage! 

Please, stop to focus on the MotherX4 dioles... It is a solution for around 250 happy users.
The problem is your dangerous fix posted on cpc-wiki :



Returning the external PSU current into the CPC VCC line... 
Please, clean behind your house first. Thanks.

@robcfg From my tests, it is recommanded to use an external PSU if you are using more than three expansions, to save your CTM life.

[robcfg]

@LambdaMikel , don't get me wrong, but diodes are not only there to drain voltage, but to protect from possible problems.


Now, if certain designs don't take that into account, it's a whole different issue.

[LambdaMikel]

@LambdaMikel , don't get me wrong, but diodes are not only there to drain voltage, but to protect from possible problems.


Now, if certain designs don't take that into account, it's a whole different issue.

@robcfg, all I am suggesting is to put a jumper on board that disables this voltage dropping diode for people that do not require an extra PSU feeding into the MotherX4. I think you could understand that. You and I both know what a voltage protection diode is and what it's purpose is, yes.

[LambdaMikel]

Need more voltage? Input more voltage! 

Unncessary and dangerous. Why add fire to the house if you don't need it.