The F18a DIY alternative with HDMI :)

[retrocanada76]

so I added to the project the FAT version. It is not tested, just for you to know  and it is auto-routed. I don't have time to route them by hand  

[retrocanada76]

the VDP orientation on the FAT is opposite the pin 1 is torwards the HDMI SIDE. It should fit on TI 99 4/a. "Should"

 

[retrocanada76]

I updated the silk showing the TMS half-moon and the pin one orientation to avoid mistakes. 

 

[weirdocollector]

_{Fantastic job!}

_{Does this uses the old SDRAM on board of the Nabu pcb, or its own internal VRAM?}

[retrocanada76]

internal RAM 16KB. There is no support for external DRAM (nor do I have pins)

[Hans23]

Here's a placement proposal for a more compact PCB using SMD components:

 

This is the underside of the board, facing towards the TMS99xxA socket.  The jumpers are replaced by solder pads on this side so that they can be reconfigured even if the FPGA board is soldered onto the other side.  Pads are only provided for those pins of the VDP that are needed, with four extra pads for 1, 2, 39 and 40 to provide some mechanical support.  To yield the minimum height of the stack, single pins like the ones used in the original F18A can be used.  The holes are a little smaller to make mounting machined pins easier.

I am unsure about the VGA connector - In this version, I've integrated the DAC onto the board so that a simple cable can be used to provide the VGA output and no second PCB is required.  Using a flatflex connector and cable like in the MK1 would be possible and potentially reduce the footprint to that of the FPGA board, but I feel that the connector and cable aren't all that DIY friendly.  Any opinions?

 

 

This is the component side - The idea would be to solder on the FPGA board using machined pins.  The minimum stack height will be defined by the SD card socket, and one will probably be able to get away using normal machined pin strips with plastic spacers.

 

Any ideas and feedback would be greatly appreciated before I send out a production order to test it.

 

Thanks go to @matthew180 for designing the F18A and @retrocanada76 for porting it to the Tang Nano 9k!

[retrocanada76]

looks cool but will it fit a TI99 ? I guess not because the VPD is facing down, the HDMI connectors there are hitting the case.

 

Also, I found that the VGA header and the HDMI on the same side a bit bulky. On NABU i had plenty of space but the TI99 ?

 

The HDMI pins are accessible on the board, the yellow boxes. What if we used a mini-hdmi on the board ? Would that work ? Then we could add a mini-hdmi to hdmi extension cable inside de computer. I have mini-hdmi but sometimes it's all we can have.

 

We could even remove the HDMI port for a smaller profile then depending on the host. The SD card reader under could also be extracted.

 

For the TI I think we should not go down but to the left. And the VDP must be 180 degrees rotated. Look my FAT board I commited to the repo. We can try using a right angle HDMI on the TI99 but only experimenting.

 

Last resort we can make a board that pulls the VDP pins using IDC socket and a 40 flat cable.

 

: 

[Hans23]

There is enough clearance in the TI-99/4a:

 

 

 

The crystal is pretty close, but it should be alright.  I've left the original VDP installed to make the photo, but the actual stack would not be as high.  I believe that the board can have the same form factor as the FPGA board when it sits underneath, and that the VGA connector would best be an 16 pin IDC footprint that can be snapped off if it is not needed.  My thinking is that most people will want either VGA or HDMI and make the decision at installation time.

 

Thoughts?

[retrocanada76]

good but mind the VDP orientation on your design. Looks like it is using NABU's while the TI has is on the other way. check the pin one of the VDP.

[retrocanada76]

i am looking at some pictures on the internet. Where is the pin 1 of the VDP on your board ?

[retrocanada76]

here the pin one is facing downward. If you put your board here, the HDMI would be pointing up what does not fit right ? 

 

[Hans23]

16 minutes ago, retrocanada76 said:

here the pin one is facing downward. If you put your board here, the HDMI would be pointing up what does not fit right ? 

 

Good point.  The HDMI output needs to point to the bottom of the board as per your picture.  I'll rotate it accordingly.

[Hans23]

Like this, maybe?

 

 

 

The VDP socket is now slightly off-center to provide enough clearance for the crystal.  Length-wise, it sits in the middle of the FPGA board so that the overhang is somewhat symmetrical.  I think this should work well with the power supply bars on the TI-99/4A motherboard which could otherwise interfere.  The MK1 approach is to make it fit into the DIL-40 footprint so that it works with all systems.  With the Tang Nano 9k, there will probably have to be a couple of different versions to accommodate different systems.

 

I wonder:  How important is it really to have both VGA and HDMI outputs at the same time?  Any opinions?

[JasonE]

The smaller footprint would work so much better in the Coleco Adam. I never put the cover back on even with the relocation board because of the amount of trimming required.

[retrocanada76]

i guess you could put optional right angle headers for the jumper, so it's up to the user to populate them or just use the solder jumpers.

[retrocanada76]

other than that it is looking good, very small

 

[retrocanada76]

You left a 4 pin distance from the vpd to the tang, will this fit the case ? don't forget the tang has a usb-c connector up there and The vdp is very close.

[retrocanada76]

look this. Better to print the board on paper and make a mechanical test

 

[Duewester]

You guys are making my brain hurt.

I haven't even wrapped by head around getting the Gerber files originally mentioned.

AND yes, pin 1 on the TI/99-4a VDP is towards the center of the board.

Edited May 4, 2023 by Duewester

[retrocanada76]

47 minutes ago, Duewester said:

You guys are making my brain hurt.

I haven't even wrapped by head around getting the Gerber files originally mentioned.

AND yes, pin 1 on the TI/99-4a VDP is towards the center of the board.

what I am saying is that Hans design will put the piggyback board too close to the case or touching it. making it impossible to fit. 

 

For the ti 99 it would be better to use the FAT version of my board. Here the gerbers:

 

https://github.com/lfantoniosi/tn9k_f18a/tree/main/KiCad/tn9k_f18_fat/gerber

 

and for the VGA module:

 

https://github.com/lfantoniosi/tn9k_f18a/tree/main/KiCad/tn9k_vga/gerber

 

 

[Hans23]

I have a couple TI-99/4A to test my layout with, and I certainly will make sure there is enough clearance.

[Hans23]

Here's my latest layout - I've added the VGA connector as a snap-off part.  It can be used in place or snapped off, depending on the use case.

 

 

 

I've adjusted the positions yet again so that there is more clearance towards the back of the TI-99/4A case.  I'm not going to put in jumper headers as I feel that the solder configuration jumpers are enough and I don't know where to fit jumpers anyway.

[Duewester]

Here's my idea for running the HDMI under the Fat or Narrow board.

I'm still waiting on my PCB's but I have my Nano and all the other parts. I have them kinda laid out on a breadboard and ran these parts (from spares and broken parts - new ones on order) under as a "Proof of concept". I think the 30cm flat cable will work well with getting outside the TI and to some form of connector box. The parts are Adafruit parts but I had to order the socket from Digikey. This adds about $16 USD to the cost but that's close to what a HDMI cable would cost anyway. You could probably get by with the 20cm flat cable but I went 30cm to be more flexible with my location of the socket. I haven't done a TI dry fit yet. I'm waiting on the PCB's for that. My concern is that the plug might interfere with the power bar. Time will tell.

Edited May 10, 2023 by Duewester

[Duewester]

On 5/3/2023 at 9:54 AM, retrocanada76 said:

looks cool but will it fit a TI99 ? I guess not because the VPD is facing down, the HDMI connectors there are hitting the case.

 

Also, I found that the VGA header and the HDMI on the same side a bit bulky. On NABU i had plenty of space but the TI99 ?

 

The HDMI pins are accessible on the board, the yellow boxes. What if we used a mini-hdmi on the board ? Would that work ? Then we could add a mini-hdmi to hdmi extension cable inside de computer. I have mini-hdmi but sometimes it's all we can have.

 

We could even remove the HDMI port for a smaller profile then depending on the host. The SD card reader under could also be extracted.

 

For the TI I think we should not go down but to the left. And the VDP must be 180 degrees rotated. Look my FAT board I commited to the repo. We can try using a right angle HDMI on the TI99 but only experimenting.

 

Last resort we can make a board that pulls the VDP pins using IDC socket and a 40 flat cable.

 

: 

You got me thinking here about breaking out the the HDMI. This might be just the ticket.

There is a socket version as well but it's a little too bulky (IMHO).

 

[Duewester]

Well, this almost sux. I opened up my Frankennine to dry fit the nano board and realized that I had at one time had to replace a ram chip. It just happened to be the one where the nano goes.

But maybe no worries since the ram isn't used in this mod. I'll just pull the modded chip out.😁

Now if I pull the HDMI connector off the nano and wire into the board and use the breakout, the chip won't be an issue (other than maybe being too high for the nano without adding some clearance).