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I made a Colecovision on a breadboard


nanochess

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Hi all.

 

For a whole year I've been collecting components for repairing my aging Colecovision consoles (I have two), and for a long time, I had the idea to build a simplified one on a breadboard.

 

I decided to start by building a video board, but apparently I got some non-working video chips, and it stalled me but fortunately I decided to order video chips from another seller.

 

I restarted the project by doing a Z80 board with 8K of EPROM, and 2K of RAM, along a memory decoder compatible with the Colecovision.

 

Once the Z80 was working, and I got the new VDP chip, I put together both boards and managed to get a working Colecovision BIOS screen. In the next two days I built the interface for sound, cartridge, and joystick (only one controller).

 

I think for being a hobby it came out pretty nice!

 

At the same time, I was willing to try some video editing and I got hooked!

 

First milestone: Z80 board.

 

 

Second milestone: VDP board.

 

https://youtube.com/shorts/-0sjp-fSgOk?feature=share

(for some reason this couldn't be embedded)

 

Third milestone: Cartridge connector.

 

 

And the last milestone: The joystick interface

 

 

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I'm curious, nanochess, what are the hardest components to source for a project like this? The VDP or the sound chip? I know that modern Z80 chips can be put in 3.58 Mhz mode, so sourcing the CPU shouldn't be much of a problem even nowadays.  :)

 

EDIT: Also, what kind of power does your breadboard prototype use? Does it need the same 12V/+5V/-5V power supply?

Edited by Pixelboy
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7 hours ago, Pixelboy said:

I'm curious, nanochess, what are the hardest components to source for a project like this? The VDP or the sound chip? I know that modern Z80 chips can be put in 3.58 Mhz mode, so sourcing the CPU shouldn't be much of a problem even nowadays.  :)

 

EDIT: Also, what kind of power does your breadboard prototype use? Does it need the same 12V/+5V/-5V power supply?

The VDP is the most difficult one. I had to order from four different suppliers,  only one could supply a working VDP. I suspect there are remarked chips, but I'll test later.

 

The sound chip isn't hard to get.

 

Interestingly it was hard to find a 4mhz Z80 and 2K RAM, so I got a 6mhz one.

 

It operates on a single power supply of 5V+

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13 hours ago, nanochess said:

The VDP is the most difficult one. I had to order from four different suppliers,  only one could supply a working VDP. I suspect there are remarked chips, but I'll test later.

Interesting... I'm wondering if the VDP could be reproduced by a cheap FPGA chip.

 

As I understand it, the CollectorVision Phoenix implements most (if not all) components inside a single FPGA chip, but the idea here would be to have the original ColecoVision architecture with a real Z80 CPU, but with hard-to-find auxiliary components (like the VDP) replaced with small FPGAs that are easier to source yet relatively cheap. Could that be done?

 

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4 hours ago, Pixelboy said:

Interesting... I'm wondering if the VDP could be reproduced by a cheap FPGA chip.

 

As I understand it, the CollectorVision Phoenix implements most (if not all) components inside a single FPGA chip, but the idea here would be to have the original ColecoVision architecture with a real Z80 CPU, but with hard-to-find auxiliary components (like the VDP) replaced with small FPGAs that are easier to source yet relatively cheap. Could that be done?

 

I think yes, but finding an inexpensive FPGA is almost as hard as tracking a TMS9118.

 

3 hours ago, 1980gamer said:

Very nice @nanochess

 

I am betting that you don't have a cat for a pet.

 

 

In fact, I've a turtle, and it grew up from a stamp size to bigger than my hand in only two years! But happily it doesn't jump over my breadboards :rolling:

 

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1 hour ago, nanochess said:

I think yes, but finding an inexpensive FPGA is almost as hard as tracking a TMS9118.

So a TinyFPGA like the ones listed here would not be quite sufficient?

 

I don't know how many logic cells one needs to replicate the TMS9918.  :)

 

EDIT: Here's an excerpt from a Wiki page about the TMS9918: "The difference between TMS9918A and TMS9928A is that the '1' version outputs composite NTSC video, while the '2' versions (including the TMS9929A) outputs analog YPbPr." So for your "breadboard prototype", the ColecoVision wouldn't care if it's a 9918A or 9928A?

 

Edited by Pixelboy
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47 minutes ago, Pixelboy said:

So a TinyFPGA like the ones listed here would not be quite sufficient?

 

I don't know how many logic cells one needs to replicate the TMS9918.  :)

 

EDIT: Here's an excerpt from a Wiki page about the TMS9918: "The difference between TMS9918A and TMS9928A is that the '1' version outputs composite NTSC video, while the '2' versions (including the TMS9929A) outputs analog YPbPr." So for your "breadboard prototype", the ColecoVision wouldn't care if it's a 9918A or 9928A?

 

The '18A outputs composite. The '28A outputs luminance and color difference. This is different than YPbPr (math required to convert). Either way, it's more circuitry. The easy way is to just use an '18A, except you get the rainbow effect. If you're using a '28A for experimentation, you could just tap into the Y, and get a black & white picture.

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1 hour ago, Pixelboy said:

So a TinyFPGA like the ones listed here would not be quite sufficient?

 

I don't know how many logic cells one needs to replicate the TMS9918.  :)

 

EDIT: Here's an excerpt from a Wiki page about the TMS9918: "The difference between TMS9918A and TMS9928A is that the '1' version outputs composite NTSC video, while the '2' versions (including the TMS9929A) outputs analog YPbPr." So for your "breadboard prototype", the ColecoVision wouldn't care if it's a 9918A or 9928A?

 

It looks cool! I would need to research this.

 

I think there is already an open source TMS9918 core with VGA output. However, I would need to study how to generate a TV output.

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1 hour ago, 5-11under said:

The easy way is to just use an '18A, except you get the rainbow effect.

I actually had to look that up, and it brought back memories of playing games on my ADAM with a CRT television back in the eighties.  :D

 

I'm guessing it would be challenging to correct the TV output on the fly to get a clearer picture, which is why Matthew went the VGA route with his F18A.  :)

 

EDIT: I just noticed the dedicated speaker on the breadboard in the video. Is it difficult to output sound to the TV?

 

Edited by Pixelboy
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3 hours ago, Pixelboy said:

I actually had to look that up, and it brought back memories of playing games on my ADAM with a CRT television back in the eighties.  :D

 

I'm guessing it would be challenging to correct the TV output on the fly to get a clearer picture, which is why Matthew went the VGA route with his F18A.  :)

 

EDIT: I just noticed the dedicated speaker on the breadboard in the video. Is it difficult to output sound to the TV?

 

The TMS9118 generates composite video, so it would one plug for video and another for audio. However, I didn't had another plug, so I opted for a tiny speaker. But yes, it is easy to output sound to TV.

 

The Colecovision combines both signals into the RF.

 

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23 hours ago, Pixelboy said:

I'm guessing it would be challenging to correct the TV output on the fly to get a clearer picture, which is why Matthew went the VGA route with his F18A.  :)

Yes it can get fairly complicated to produce a clean standard video output from the TMS. I've been having fairly good results using an LM1889, CD4066, FMS6400, and a handful of other parts to make it happen.

 

Here's what I'm getting presently with an S-Video output...

1878531432_CV-NUC_S-Video_V1.4.png.148c7

 

That's quite a mess of wires for sure...

BITD this would have been my approach as well, but now days with cheap PCBs i would never dream of doing it that way again. My hats off to you @nanochess on not only persevering, but also getting it to work.

 

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On 2/24/2023 at 11:32 AM, nanochess said:

 

In fact, I've a turtle, and it grew up from a stamp size to bigger than my hand in only two years!

 

Just when I thought I couldn't have any more respect for you than I already do... you post this!  :D

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On 3/1/2023 at 5:51 PM, leaded solder said:

That's a good build, congrats! Using the 9118 to shave most of the video DRAMs is a good improvement too.

Thanks! It also provides the clock signal for the whole system.

 

BTW, I built the VDP tester breadboard, and only one VDP is non-working. 

 

20230227_123750.jpg

20230227_124726.jpg

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