MotherX4 Alternative for CPC 464 Users

[LambdaMikel]

Out of "frustration" that my DDI3 cannot be easily connected to the Mother X4 (as it has no edge connector, and with a cable the voltage drop is too high for the DDI3 to work), I have designed an alternative. I'll make the Gerbers available if it works.

[rpalmer]

lambdamikal,

I already have a version of the MX4 available (see attached)

Rpalmer

[LambdaMikel]

lambdamikal,

I already have a version of the MX4 available (see attached)

Rpalmer

That's nice.
And it has an edge connector for my DDI3 at the end?
If so, where can I download the Gerbers.

[rpalmer]

lambdamikel,

There are no edge connectors, but an adapter can be used to connect it to the IDC socket to allow for original peripherals.

rpalmer

[LambdaMikel]

lambdamikel,

There are no edge connectors, but an adapter can be used to connect it to the IDC socket to allow for original peripherals.

rpalmer

Palmer,


see, this is exactly what I wish to avoid with that.


I have a solution with cables and adapters (a couple of my CPC Connectors plugged together and cables) that works for DDI3, but it is ugly and not very reliable. And, if paired with MotherX4, results in a voltage drop which renders the DDI3 non functional.


Hence this board.

[LambdaMikel]

lambdamikel,

There are no edge connectors, but an adapter can be used to connect it to the IDC socket to allow for original peripherals.

rpalmer

Also, not sure what you mean with original peripherals.
No matter what, you need an edge connector if you wish to use an original CPC 464 hardware extension such as the DKtronics speech synth or the DDI3. Where do I get an edge connector from otherwise.

[revaldinho]

I had the same problem - 464 and DDI-3 but wanting to use other cards too - but I solved it in a different way.


I took one of your own adapters, hacksawed off the edge connector and mounted it vertically on the back of the DDI3 using one set of connector holes. I put a 50W box header in the other set. So now I have the DDI3 directly plugged into the CPC464 and an expansion card connected at the back.


The snaps are a lot clearer than my description 

[LambdaMikel]

I took one of your own adapters, hacksawed off the edge connector and mounted it vertically on the back of the DDI3 using one set of connector holes. I put a 50W box header in the other set. So now I have the DDI3 directly plugged into the CPC464 and an expansion card connected at the back.

Good idea and very creative unintended use of the adapter! 
I don't want to modify my DDI3 for this though. 
Glad it works for you!

With the new LambdaBoard, the DDI3 will be at the far end, and a single cable from the CPC 464 edge connector will go into the board. That should also increase physical stability since the DDI3 is quite heavy. And the edge can also be used to connect the DDI and DKtronics and the like at the end then without putting stress on the CPC motherboard's edge.

[rpalmer]

I have a solution with cables and adapters (a couple of my CPC Connectors plugged together and cables) that works for DDI3, but it is ugly and not very reliable. And, if paired with MotherX4, results in a voltage drop which renders the DDI3 non functional.

Don't forget the Right Angle board also allows for an independent 5V supply as well, so that should mitigate power supply issues to expansion cards.

rpalmer

[LambdaMikel]

Don't forget the Right Angle board also allows for an independent 5V supply as well, so that should mitigate power supply issues to expansion cards.

MotherX4 also has one, and I am not using it to avoid cable clutter. Someone suggested that one of the reasons for the voltage drop
might be the diode on the MotherX4. It should not be necessary to have an external additional PSU for a DDI3 and 2 or 3 more cards.
So, hopefully, the LambdaBoard will just work fine like that.

[rpalmer]

lambdamikel,

There is one other aspect to power supply issue and that is that the CPC was probably not mean't to have many expansions all drawing on the same 5V.

I mean just adding the DDI3 in some respects may be enough to drop the voltage to a point where other expansions may cause problems (and the same could be from other expansions).

There is also the age of the machine which maybe a factor in all of this.

The simple act of adding a bus extension card should not in theory cause any issues.

rpalmer

[LambdaMikel]

Palmer.

I believe that is a design flaw in the MotherX4. I don't have these voltage drop issues with the same PSU and CPC 464 if I connect a couple of my CPC connectors together with cables (ugly, but works). I will see how well it works with the DDI3 when the PCB arrives (next weekend). 

[Duke]

On MotherX4, you could add a simple switch to bypass the diode, to avoid the voltage drop (of course don't feed the ext. power, when bypassing the diode coming from the CPC VCC line).

[LambdaMikel]

On MotherX4, you could add a simple switch to bypass the diode, to avoid the voltage drop (of course don't feed the ext. power, when bypassing the diode coming from the CPC VCC line).

Right, I heard somebody has done that successfully. But even with that mod in place, I still want an edge for the DDI3's edge connector at the end such that I only need one cable in that setup. The less cables and connectors, the better from a reliability and voltage drop point of view 

[Duke]

The less cables and connectors, the better from a reliability and voltage drop point of view 

I agree - I would crank up your VCC and GND lines, as you have plenty of space. I think with the 7-8 mil tracks you can draw about 800 mA on 1 oz copper, it's probably fine, but just for the sake of it

[Bryce]

A bit off topic, but for those of you who are designing PCB routing/layouts, there's a great free program from SaturnPCB that will help you calculate PCB traces for current, voltage, stand-off etc, which every PCB designer should have on their PC:
http://www.saturnpcb.com/pcb_toolkit.htm
Many aspects of it aren't required for retro computing (there's a lot of high-frequency calculators), but the basics still apply.

Bryce.

[LambdaMikel]

I agree - I would crank up your VCC and GND lines, as you have plenty of space. I think with the 7-8 mil tracks you can draw about 800 mA on 1 oz copper, it's probably fine, but just for the sake of it

Yes, that might be a good idea... However, here is a question. In my understanding, the effective width of a track is determined by its narrowest part / segment, and that is already determined by the connector pin as well as the leads within the CPC going to the edge connector. How can a thicker / wider track make any difference if the narrowest part is before that segment? Also, the connector pin will have poor conductivity as well.

So, I think there are certainly good design patterns and best practices, including
- backside copper GND plane
- decoupling capacitors for each chip
- large width of tracks etc.
but I doubt that these are really strictly necessary for the current, voltage and frequency ranges the CPC operates at. Just my 2 cents    I am probably wrong though.

[Duke]

The CPC mainboard has huge power and gnd traces, like 30 mil or more, but otherwise I agree that it wouldn't make sense to beef them up if the former had smaller width. Just isn't the case.
And we already know what poor connectivity for the edge connector means (==trouble), so thats why it's essential to clean up the edge connector for proper operation.
Maybe it isn't a problem to power 4 devices with a 7.5 mil, 1 oz track , but it certainly could be and when you have plenty of space, I see no reason not to do it

Yes, that might be a good idea... However, here is a question. In my understanding, the effective width of a track is determined by its narrowest part / segment, and that is already determined by the connector pin as well as the leads within the CPC going to the edge connector. How can a thicker / wider track make any difference if the narrowest part is before that segment? Also, the connector pin will have poor conductivity as well.

So, I think there are certainly good design patterns and best practices, including
- backside copper GND plane
- decoupling capacitors for each chip
- large width of tracks etc.
but I doubt that these are really strictly necessary for the current, voltage and frequency ranges the CPC operates at. Just my 2 cents    I am probably wrong though.

[LambdaMikel]

The CPC mainboard has huge power and gnd traces, like 30 mil or more, but otherwise I agree that it wouldn't make sense to beef them up if the former had smaller width. Just isn't the case.

I could have sworn that I saw some skinny traces there, but I looked at the 464 board again, and you are right, they are indeed quite thick!  I changed to 15.75 mils (0.4 mm) - double the width I had previously, and not only for GND and VCC, but for all. I think that should really be sufficient now.

[Bryce]

Yes, that might be a good idea... However, here is a question. In my understanding, the effective width of a track is determined by its narrowest part / segment, and that is already determined by the connector pin as well as the leads within the CPC going to the edge connector. How can a thicker / wider track make any difference if the narrowest part is before that segment? Also, the connector pin will have poor conductivity as well.

Almost correct: The length of the thinnest part of track is also part of the equation. Also remember, that the volume of the conductor is also important, so the pins may be narrow, but they are much thinker and have more copper volume. Check out the "conductor Properties" tag in the Saturn PCB Toolkit software I recommended lately.

Not important in this case, but the frequency of the signal is also an important part of the equation.

Bryce.

[LambdaMikel]

The first version (thin tracks) is back. No problems so far 

[Bryce]

There's more electronics outside your CPC than in it!

Bryce.

[LambdaMikel]

There's more electronics outside your CPC than in it!

Happens with my Amiga 500, too - same rights for all retro computers please 

[LambdaMikel]

Happens with my Amiga 500, too - same rights for all retro computers please 

In case somebody has too much money:

https://www.sellmyretro.com/offer/details/lambdaboard-expander-32272

[LambdaMikel]

I'll make the Gerbers available if it works.

As promised, for those who want to build it themselves:
https://oshpark.com/shared_projects/fCGxBoNY
Take advantage of my CPC community assembly service otherwise