[Coco] [!! SPAM] Re: [!! SPAM] Re: [!! SPAM] Re: Coco compatible monitors...

[gene heskett]

On Sunday, July 03, 2011 09:13:16 AM John Kent did opine:

> On 3/07/2011 12:43 AM, gene heskett wrote:
> > I think that is the general idea Roy's device uses, along with a
> > couple of pots to scale the a/d response to the machine.  It is quite
> > usable, with some reservations about the blue because the tendency to
> > set the pots to reduce the digital background noise also takes away
> > some of the gain, and since the blue is the least amplitude, it
> > suffers.  I think this may be a characteristic of my gime also, and
> > if some way to enhance the gimes rise and fall times could be found,
> > that would alleviate much of the problem.
> > 
> > Unforch, the output stages in the gime were apparently on a power
> > budget. Mine has rise&  fall times in the 400ns range.  Since the cm8
> > was also severely limited, so severely that trading it for a Maggy
> > 515 was a huge improvement, but even that never made a blue 80 column
> > text screen readable.
> > 
> > I have no clue if raising the VCC on the gime would help, never tried
> > it, basically because if you push the envelope and blow the gime,
> > there aren't any replacements other than raiding another coco3. It
> > might be amazing what 6 volts on the VCC pin might do for it.
> > 
> > I have even considered sampling the memory signals and making my own
> > set of 2 bit d/a's to replace the gime's anemic output stages, but I
> > need to make some round tuits first as I have people clamoring for
> > them.  Still looking for suitable artwork for (preferably 2
> > difference faces so there is a heads and a tails sides) that.  What I
> > have found on the net is either way too complex to try to put on a 50
> > cent sized coin due to the carving time involved (a whole page of
> > text), or best described as ugly.  Graphics files for something
> > attractive gratefully accepted.
> > Cheers, gene
> 
> Hi Gene,
> 
> One solution maybe to replace the GIME chip with an FPGA. The only issue
> though would be to have 5V tolerant I/O as most FPGAs have 3.3V I/O and
> 1.8V (?) for the internal core which would require a few regulators.
> Gary has a GIME clone in his CoCo3FPGA, so it would make sense for him
> to extract that and put it in say a 200Kgate Spartan 3 if it would fit.
> I'm not sure if the video I/O from the GIME chip is multilevel or not.
> Some video chips have a multi-level ladder circuit for generating
> analogue Y-UV output.
> 
The gime's pallette is somehow extracted from a 2 bit d/a on each color, 
for a 4 level per color lashup.  Now if this FPGA in a Spartan 3 could just 
drop into the gime socket, I could get interested.  Real interested.  
Running a 63C09, and a 2 meg disto memory kit, all on an old AT power 
supply, I have nearly zero heat, the gime is the warmest chip in it, and 
the power use in that socket could go up to several watts with a suitable 
heat sink.

I am well aware of the limitations imposed by the coco's OEM power supply 
and regulator, which could not support that power usage increase without 
active cooling.  That however is also adjustable, I have done it a couple 
of times now.  That very inefficient analog design is 90% of the emitted 
heat in a box stock coco.  It can drive a small 12 volt dc fan from the 
output of the rectifier, and this is a huge help in maintaining reasonable 
internal temps.  Whether that additional 150 ma is still within the design 
envelope of that transformer I don't know, but I have a coco2 and a coco3 
equipt with fans, and the coco2 ran 24/7 for 13 years, with 2 drive 
controller failures.  The lack of a 3 pin power plug on the drive boxes and 
the coco2 meant that when the studio tower was being used as a lightning 
rod by mother nature, the resultant EMP surges were pretty hard on the 
controller.  I eventually married them all together with copper braid, 
grounded to the rack.


> Round tuits ? I have plenty of uncompleted projects too.
> 
> John.


Cheers, gene
-- 
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