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Grogster

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Posted: 01:53am 08 Jun 2023

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Hello all.

I note that in the latest PM manual(5.07.07 Rev 2), page 6, the circuit for the interface to the VGA socket is MUCH more simple then the other older version, reduced to just four resistors, and the trim-pot and diodes are removed completely.

That is great, cos it is easier to design into a PCB with less components to place, but can I just check that this new version of the circuit, is not a result of some changes to the FW in the VGA department?

IE: Can I use the latest FW versions with EITHER the old circuit OR the new one as shown on page 6 of the latest manual?

I've already designed several VGA boards that all use the older more complicated VGA circuit, and I have no desire to change/hack the existing PCB, just to use the latest FW.

I am hoping that there has actually been NO CHANGE to the way the PM outputs the VGA, rather just that this simplified circuit is now the one to use over the older one.

Yes?

Smoke makes things work. When the smoke gets out, it stops!

phil99

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Joined: 11/02/2018
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Posted: 02:05am 08 Jun 2023

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No change to the firmware. The simpler DAC may produce slightly different colours however with just 4 bits only 16 colours in the 24 bit set are correct anyway.
The choice is between approximately wrong or exactly wrong!

Grogster

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Posted: 03:12am 08 Jun 2023

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Lovely, thanks.

I just wondered if the FW VGA had been tweaked to use the simpler interface circuit.
Glad that is not the case - on with the next layout!

Smoke makes things work. When the smoke gets out, it stops!

Mixtel90

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Posted: 06:30am 08 Jun 2023

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No changes at all. I've been using the 4-resistor version on my boards for a while now. On my monitor I can't see any difference (or maybe my glasses needed cleaning when I was comparing them).

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

stanleyella

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Joined: 25/06/2022
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Posted: 04:33pm 08 Jun 2023

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Mixtel90 said No changes at all. I've been using the 4-resistor version on my boards for a while now. On my monitor I can't see any difference (or maybe my glasses needed cleaning when I was comparing them).

I said before the multi turn pot did not make a noticeable difference to me and I had to order 5 and the diodes.
The new vga circuit will be fine if I try it I bet.

Mixtel90

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Posted: 04:44pm 08 Jun 2023

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The original circuit has the potential to be more accurate and may give better results with some monitors. However most people are unlikely to see the difference unless they are comparing the two. The 4-resistor version is certainly a lot easier to lay out on a PCB. :)

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

ice2642

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Joined: 27/05/2023
Location: Brazil
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Posted: 04:51pm 08 Jun 2023

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Any of you guys know if the VGA model used by Silicon chip VGA PicoMite https://www.siliconchip.com.au/Shop/20/6417?show_parts_list=1
Are the new or the old one?

Tkz in advance.

MMBasic 5.0707 on PicoMite VGA

Volhout
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Posted: 05:10pm 08 Jun 2023

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The multiturn pot in the original design allows you to set the white balance (for bright white). But adjustment may affect other colors.

Volhout

PicomiteVGA PETSCII ROBOTS

Mixtel90

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Posted: 05:14pm 08 Jun 2023

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Dunno. We don't get Silcon Chip in the UK. Not unless some of it is repeated in Practical Electronics months later. And I can't find that on the shelves either nowadays. The list of resistors on the linked page makes me think it may be something different again.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

stanleyella

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Posted: 06:43pm 08 Jun 2023

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Volhout said The multiturn pot in the original design allows you to set the white balance (for bright white). But adjustment may affect other colors.

Volhout

I guess my vga monitors adjust themselves for the signal.

Turbo46

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Posted: 09:59pm 08 Jun 2023

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I believe that the Silicon Chip VGA circuit is Geoff's design, you can see it here scroll down and download the construction pack, it is Design #1 in there.

It is the old design with the pot. I suppose you could use the 'new' design's components and link out the unused bits but if you are getting all of the old components why not fit them.

By the way, that design does not include sound.

Bill

Keep safe. Live long and prosper.

ice2642

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Posted: 01:39am 09 Jun 2023

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Turbo46 said I believe that the Silicon Chip VGA circuit is Geoff's design, you can see it here scroll down and download the construction pack, it is Design #1 in there.

It is the old design with the pot. I suppose you could use the 'new' design's components and link out the unused bits but if you are getting all of the old components why not fit them.

By the way, that design does not include sound.

Bill

So it is,

I bought this kit, I'm hoping to get it, I just found it on Geoff's website. I thought buying the kit would help the author in some way rather than buying everything separately.

I'm thinking of making a small sound card or buying a DAC on aliexpress and connecting somehow through the card's GPIO pins.

Hope it works.

MMBasic 5.0707 on PicoMite VGA

Mixtel90

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Posted: 06:35am 09 Jun 2023

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DAC support is new and AFAIK will only work with the MCP8022 family (the 22 is 12-bit). There's no point in looking at anything else.you need to connect it to a hardware SPI port, which can't be shared with anything else, using the SPI OUT and CLOCK lines plus a CS pin. There is an OPTION AUDIO x, y, z for setting it up, but I can't remember the order of the arguments. :)

The output filter is simple. A 150R resistor followed by a 100nF capacitor to GND. It's a pretty high output level at about 2V.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

Volhout
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Posted: 10:40am 09 Jun 2023

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MCP4822 (not 8022)

PicomiteVGA PETSCII ROBOTS

ice2642

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Posted: 12:05pm 09 Jun 2023

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Mixtel90 said DAC support is new and AFAIK will only work with the MCP8022 family (the 22 is 12-bit). There's no point in looking at anything else.you need to connect it to a hardware SPI port, which can't be shared with anything else, using the SPI OUT and CLOCK lines plus a CS pin. There is an OPTION AUDIO x, y, z for setting it up, but I can't remember the order of the arguments. :)

The output filter is simple. A 150R resistor followed by a 100nF capacitor to GND. It's a pretty high output level at about 2V.

Volhout said MCP4822 (not 8022)

Thank you for information.

Do you found some kind of breakout board in aliexpress using the MPC48x2?

I ask just about Aliexpress because the shipping cost. for idea, the board from silicon chip shipping was $30,00 dolar, if I bought the parts on aliexpress, I wold expend in shipping less than 4 dolar.

Best Regards,

MMBasic 5.0707 on PicoMite VGA

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