Understanding the Vectrex

Sebastian Brueckner

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Dec 31, 2011, 4:52:17 AM12/31/11

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Hi all,

I have been reading some about the Vectrex and built my own
integrating vector generator driven by a moden microcontroller. It
works suprisingly well using an oscilloscope as screen.

However there are some questions that I dod not figure out yet, maybe
someone can give me a hint:

How does the vectrex make sure that vectors of different length have
the same brightness?

I read that scaling of vectors is done by changing the integration
time. What is the integrator reference voltage ZERO REF used for?

Best Regards,
Sebastian

Mittens

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Dec 31, 2011, 6:40:54 AM12/31/11

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On Sat, 31 Dec 2011 09:52:17 -0000, Sebastian Brueckner
<sdbru...@gmail.com> wrote:

> I have been reading some about the Vectrex and built my own
> integrating vector generator driven by a moden microcontroller. It
> works suprisingly well using an oscilloscope as screen.
>
> However there are some questions that I dod not figure out yet, maybe
> someone can give me a hint:
>
> How does the vectrex make sure that vectors of different length have
> the same brightness?

I'm not sure it does: I think it's up to the game designer to make sure
the vector run lengths within a sprite are fairly evenly matched. Having
said that the response of the phosphor in the CRT is very non-linear,
exhibiting both fluorescence (immediate response to the electrons striking
the screen) and phosphorescence (re-emission). These effects to even out
the brightness of the lines somewhat.

> I read that scaling of vectors is done by changing the integration
> time.

Yes, I think that's correct.

> What is the integrator reference voltage ZERO REF used for?

Do you mean the voltages derived from the pots R333 and R335? They are
there to try and offset any bias in the integrator op-amps or leakage in
the other components. If you rebuilt it with modern op-amps I suspect
these might not be required.

As you are interested in building a vector machine from scratch, I wonder
if you have looked at the Forbes scope clock? IMHO the line drawing scheme
that uses is superior in many respects to the Vectrex, not least because
there are no issues with drift and it can draw nice curves without
intensive CPU intervention. Lots more info here:
http://www.cathodecorner.com/sc200c.html

-- mittens

Mittens

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Dec 31, 2011, 6:41:48 AM12/31/11

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On Sat, 31 Dec 2011 09:52:17 -0000, Sebastian Brueckner
<sdbru...@gmail.com> wrote:

> I have been reading some about the Vectrex and built my own
> integrating vector generator driven by a moden microcontroller. It
> works suprisingly well using an oscilloscope as screen.
>
> However there are some questions that I dod not figure out yet, maybe
> someone can give me a hint:
>
> How does the vectrex make sure that vectors of different length have
> the same brightness?

I'm not sure it does: I think it's up to the game designer to make sure
the vector run lengths within a sprite are fairly evenly matched. Having
said that the response of the phosphor in the CRT is very non-linear,
exhibiting both fluorescence (immediate response to the electrons striking
the screen) and phosphorescence (re-emission). These effects to even out
the brightness of the lines somewhat.

> I read that scaling of vectors is done by changing the integration
> time.

Yes, I think that's correct.

> What is the integrator reference voltage ZERO REF used for?

Sebastian Brueckner

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Jan 1, 2012, 1:18:26 PM1/1/12

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On 31 Dez. 2011, 12:40, Mittens <mittens@_nospam_hush.ai> wrote:
> > What is the integrator reference voltage ZERO REF used for?
>
> Do you mean the voltages derived from the pots R333 and R335? They are
> there to try and offset any bias in the integrator op-amps or leakage in
> the other components. If you rebuilt it with modern op-amps I suspect
> these might not be required.

If you look at the block diagram, there is a signal ZERO REF from the
4052 MUX to the positive inputs of the integrators.

If you move this reference voltage away from the X and Y voltages, the
difference seen by the integrators would be larger and the integration
should be faster. So I assumed this could be used to scale the
vectors, too. How is this signal used in actual Vectrex code?

> As you are interested in building a vector machine from scratch, I wonder
> if you have looked at the Forbes scope clock? IMHO the line drawing scheme
> that uses is superior in many respects to the Vectrex, not least because
> there are no issues with drift and it can draw nice curves without
> intensive CPU intervention. Lots more info here: http://www.cathodecorner.com/sc200c.html

That definately sounds appealing. I will have a look.

I have a basic Asteroids running on my AVR-Vectrex now :-)

Sebastian

Mittens

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Jan 1, 2012, 6:45:50 PM1/1/12

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On Sun, 01 Jan 2012 18:18:26 -0000, Sebastian Brueckner
<sdbru...@gmail.com> wrote:

> I have a basic Asteroids running on my AVR-Vectrex now :-)

Cool! Do you have pictures?

Sebastian Brueckner

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Jan 2, 2012, 1:31:32 PM1/2/12

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On 2 Jan., 00:45, Mittens <mittens@_nospam_hush.ai> wrote:
> On Sun, 01 Jan 2012 18:18:26 -0000, Sebastian Brueckner
>

> <sdbrueck...@gmail.com> wrote:
> > I have a basic Asteroids running on my AVR-Vectrex now :-)
>
> Cool! Do you have pictures?

I put all the pictures and videos up here:

http://www.ags.tu-bs.de/?id=e.lab:projekte:vectrex2012

Just ignore the text :-)

Sebastian

VectrexMad!

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Jan 2, 2012, 1:59:07 PM1/2/12

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That seems very interesting work; wish I could read Germanthough.
I'll try reading with translator software.

VectrexMad!
http://www.vectrex.co.uk

hcmffm

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Jan 3, 2012, 3:45:38 PM1/3/12

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Cool project, Sebastian. Make sure you let us know once your hardware
supports Vectrex game carts and is mass-produced. ;-) Honestly, I'm amazed
how quickly your project progresses!

- Helmut