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Revision of the DM65PIC-Widgetboard

  • Hi everybody,


    in this posting I wrote that I am not very satisfied with the current implementation of the DM65PIC-Widgetboard. In my opinion the board could be improved in many ways.


    I would like to do a revision of the DM65PIC-Widgetboard, but I am very unsure, whether a revision would make sense at all. Here in the forum there are only a few users that have already built this board and there is maybe no need for an improved one. Furthermore in a few months there will be a finalized and ready-to-use MEGA65 to be bought and this would bring the request for a DM65PIC-Widgetboard down to zero I guess.


    However I would like to highlight a few improvements of the DM65PIC-Widgetboard that I would like to do:


    1) CAD-System would be KiCAD instead of EAGLE

    This would be mandatory because I switched to KiCAD a few years ago.


    2) Improvement of Circuit Diagram

    I would like to draw a "function-based" circuit diagram. As an example the circuit drawing would be more readable if you group STM32-pins in the STM32-symbol for a specific function together (e.g. interface to the Nexys-Board), instead of having them in line according to their pin-number.


    3) Board-Dimensions

    I would like to mount the DM65PIC-Widgetboard right under the Nexys-Board. Therefore I would suggest to have exactly the same dimensions of the PCB as the Nexys-Board.


    4) Mounting-Holes

    With four mounting holes at each corner the DM65PIC-Widgetboard could be screwed either under the Nexys-Board or to any other base plate.


    5) Same Component Size

    For your convenience I would not go with smaller components for resistors and capacitors. I would prefer to use the same size (0805) for them so that one can easily solder them onto the PCB.


    6) Same Component References

    I would like to use the same component designators as on the original board as far as possible, so that equal functions will have the same component references. (E.g. SV2 would be the C65 keyboard connector on both the original and the improved PCB)


    7) Global Silkscreen Improvement

    I would like to do a massive improvement of the silkscreen on both sides, so that you can at least easily identify each component.


    8 ) Additional IEC-Interface

    Would it be an improvement, if an IEC-Interface for an external floppydrive would be included onto the PCB? I do not know anything about it yet, but if there will be a board revision and if an IEC-Interface would be requested then if would be the right time to include one...


    9) Using components that are easy available

    At the moment the Widgetboard contains components (e.g. On/Off-Switch, Battery-Holder) with no part-number, so that these components are difficult to buy. I would like to have a bill of material where all the components are listed and furthermore where the purchase order number of Reichelt, Mouser, Digikey and LCSC are included. With that information it would be very easy to buy all the components.



    Of course, all design files would be uploaded to my github pages and would be open-source.


    What do you think? What is your opinion on this topic? Do you have any other suggestions or should I simply stay with the original board and wait for a final MEGA65? I am eager to read your feedback!


    Cheers,

    Thomas

  • 1)

    i agree, i switched a couple of years ago too.


    2)

    fully agree

    3) Board-Dimensions

    I would like to mount the DM65PIC-Widgetboard right under the Nexys-Board. Therefore I would suggest to have exactly the same dimensions of the PCB as the Nexys-Board.

    Here i would like you to think about trhe following problems:

    The design rules for PMods are, that they should be attached to the side of the Nexys A7. If you would mount the Widget board directly under the Nexys, the height would increase quite alot (With all neccessarry ports and their heights).

    If this wouldn't be an issue, in a let's say standard C64c case, i would be fine.

    4) Mounting-Holes

    With four mounting holes at each corner the DM65PIC-Widgetboard could be screwed either under the Nexys-Board or to any other base plate.

    Yes, the mounting holes were missing in the design completely and i would suggest, to add maybe even more holes to strenghten the expansion port and the joystick ports, but use, like you metioned, the 4 corner holes to connect the Nexys A7 to the Widget.

    One idea was, to geth the mounting holes form the MEGA65 R2 board and adopt those to the widget board, then the widget board could fit in the MEGA65 case.


    5, 6 & 7)


    I agree.


    8 ) Additional IEC-Interface

    Would it be an improvement, if an IEC-Interface for an external floppydrive would be included onto the PCB? I do not know anything about it yet, but if there will be a board revision and if an IEC-Interface would be requested then if would be the right time to include one...

    100% agree. The IEC port would move the Nexys MEGA65 even closer to the MEGA65 PCB.


    9)

    Also fine with me agreed. i also had alot of trouble, finding all the parts.



    The Nexys A7 and the Widget board was my first step towards the MEGA65, i still love and use it and i believe it is still the

    cheapest, not yet easiest way to get hands on a MEGA65 (Since the soldering skills required for the widget board are quite high).

    If we only adapt the design (not change it entirely, we would keep the compatibility to the "original" widget board and would also benefit from the latest bitstreams for the Nexys A7.

  • I would like to do a revision of the DM65PIC-Widgetboard, but I am very unsure, whether a revision would make sense at all. Here in the forum there are only a few users that have already built this board and there is maybe no need for an improved one. Furthermore in a few months there will be a finalized and ready-to-use MEGA65 to be bought and this would bring the request for a DM65PIC-Widgetboard down to zero I guess.

    I think it depends on the situation, whether the Mega65 board will be sold separately or not.


    If it will be possible to buy the pure Mega65 board for (let me say) around 350 EUR, I'll see no more need for the Nexys and Widget board.


    Because if someone wants the Mega65, but wouldn't (or can't) afford the complete Mega65, he could buy the Mega65 board for the same price as the Nexys + Widget board.

  • In the past few days I tried to create a simple mock-up, to find an optimal solution for all the connectors. Threfore the following pictures are for information only and do not contain all necessary components.


    Here i would like you to think about trhe following problems:

    The design rules for PMods are, that they should be attached to the side of the Nexys A7. If you would mount the Widget board directly under the Nexys, the height would increase quite alot (With all neccessarry ports and their heights).

    If this wouldn't be an issue, in a let's say standard C64c case, i would be fine.


    3)

    Yes, mounting the widget board below the nexys board the height would be rise to approx. 45 mm total. I think that this is too much to fit into a standard c64c case...


    Therefore I think it is best to have both options, so that you can either attach the widget board to the side of the nexys board or place it underneath. Please see the next picture for reference:



    With these board dimensions and pin header placement you can easily attach the widget board aside of the nexys board by simply connecting the pmod-connectors. If you still want to stack the pcbs (as I would prefer) then you will need three additional ribbon cables (that cross the pcbs under the nexys board and above the widget board) to connect the pmod-connectors. In my opinion this solution would be a reasonable compromise.



    10) For the power supply of both boards I would suggest that you connect your nexys 5V power supply to the widget board. From here the power supply is being switched on and is being forwarded to the USB-A plug. One can either use a short "USB-A to Micro-USB"-cable to supply the nexys board from here or I will add some holes for soldering a small "power supply"-cable directly on the widget board, that can be plugged into the "low voltage"-plug at the nexys board




    11) Should I go with this arrangement of the joystick-connectors going to the side and the keyboard-connectors going to the front or should I swap both sides, so that the joystick-connectors are facing to the front side of the board?



    Cheers,

    Thomas

  • With these board dimensions and pin header placement you can easily attach the widget board aside of the nexys board by simply connecting the pmod-connectors. If you still want to stack the pcbs (as I would prefer) then you will need three additional ribbon cables (that cross the pcbs under the nexys board and above the widget board) to connect the pmod-connectors. In my opinion this solution would be a reasonable compromise.

    Fully agree. the solution with the 3 ribbon cables i use with my current widget board already.

    10) For the power supply of both boards I would suggest that you connect your nexys 5V power supply to the widget board. From here the power supply is being switched on and is being forwarded to the USB-A plug. One can either use a short "USB-A to Micro-USB"-cable to supply the nexys board from here or I will add some holes for soldering a small "power supply"-cable directly on the widget board, that can be plugged into the "low voltage"-plug at the nexys board

    That's, why the Widget board already had an USB-B connector (facing inside) and this 3 Pin connector with screws (check picture).

    Every easy solution should be fine, but as general rule, only power the Widget and feed the Nexys from there !


    11) Should I go with this arrangement of the joystick-connectors going to the side and the keyboard-connectors going to the front or should I swap both sides, so that the joystick-connectors are facing to the front side of the board?

    Here we come to an interesting design point.

    My idea was, to be able to give the community a valid solution for a lower price MEGA65.

    We have to consider the following point when designing the layout.


    The MEGA65 PCB is designed for the MEGA65 case (Joystick, power, reset, all on lefthand side of case).

    So even if, M.E.G.A will sell the MEGA65 PCB seperately at a later date, they would only fit in the MEGA65 case.

    They only would fit into a "standard" C64 breadbin or C64c case, with a lot of remodelling, drilling, etc., required.

    Also the MEGA65 keyboard doesn't fit without alot of tinkering into the c64's cases too.


    So i would suggest, that our approach should be:

    a) design the widgetboard, that it fits, from measurement size point of view, directly under the Nexys board (Your main approach)

    So people could easily design a small cube case, if it's that what they want.


    b) design the port layout (Joysticks, etc.) that they would fit in a standard C64 case, maybe with even fitting mounting holes.

    Then we could offer a valid, cheaper alternative for people to get a MEGA65.

    (which would be the crossover ribbon cable solution, to have the boards side-by-side)

    If the layout of the Widgetboard would fit with a standard c64 case, one would only need a case, where he would need to do

    minimal drilling (for the IEC port and the reset button) and could use his MEGA65 in a standard c64 case.

    Also we could remove from the current widget board design the c65 keyboard connector. i don't think, that there are many people who own an original c65 keyboard, so we would need only the c64 keyboard connector.


    With this approach, we would have an easy solution to get hands on a cheap MEGA65 as well.


    What do you think ?


    EDIT: Here is a quick 'n dirty drwaing....


  • If the layout of the Widgetboard would fit with a standard c64 case, one would only need a case, where he would need to do

    minimal drilling (for the IEC port and the reset button) and could use his MEGA65 in a standard c64 case.

    EDIT: Here is a quick 'n dirty drwaing....


    To get all the components at the positions drawn in your sketch the board needs to be significant bigger in size than it is planned now. Therefore this proposal can not be considered completely.


    I also recognized that the interest of this whole topic seems to be very limited. That is why I will continue with building the current "eagle-based" board for now, which I have populated almost completely.


    But I will not discard my ideas for a revised board at all. I think I will go on with the revision of the widget-board on a very low level within the next 3 to 6 months...



    Cheers,

    Thomas