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I'm trying to make a drum trigger to MIDI converter with a BX-35. In
order to communicate at MIDI's baud rate of 31,250 I was thinking
about either using the normal 7.3728Mhz crystal on the BX-35 and using
a MAX3100 with a 4Mhz crystal or something close to communicate. But
I've read that using SPI can cause a lot of problems. Would it be
easier to simplify things by using an 8Mhz crystal on the BX-35 while
running with a divisor of 16 to communicate at 31,250 baud? And if I
did run at 8Mhz would I be able to use COM3 at a normal baud of 9600
or 2400 for an LCD?

Thanks,
Justin





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Justin wrote:

> I'm trying to make a drum trigger to MIDI converter with a BX-35. In
> order to communicate at MIDI's baud rate of 31,250 I was thinking
> about either using the normal 7.3728Mhz crystal on the BX-35 and using
> a MAX3100 with a 4Mhz crystal or something close to communicate. But
> I've read that using SPI can cause a lot of problems. Would it be
> easier to simplify things by using an 8Mhz crystal on the BX-35 while
> running with a divisor of 16 to communicate at 31,250 baud? And if I
> did run at 8Mhz would I be able to use COM3 at a normal baud of 9600
> or 2400 for an LCD?
>
> Thanks,
> Justin
>
I found these three links which I'm sure can help you:
http://www.embeddedrelated.com/groups/basicx/show/2615.php (BasicX
group message 2615)
http://ccrma.stanford.edu/~sbacker/docs/MIDIProjectFinalDocumentation.doc
http://www.google.com/search?hl=en&q=basicx+midi&btnG=Google+Search

Regards,
Mike





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Cool, that solves the 8Mhz problem. Now, at 8Mhz would the chip's
timing for 2400 baud on com3 be off? Or would it know how to compensate?

--- In basicx@basi..., Mike Perks <basicx@a...> wrote:
> Justin wrote:
>
> > I'm trying to make a drum trigger to MIDI converter with a BX-35. In
> > order to communicate at MIDI's baud rate of 31,250 I was thinking
> > about either using the normal 7.3728Mhz crystal on the BX-35 and using
> > a MAX3100 with a 4Mhz crystal or something close to communicate. But
> > I've read that using SPI can cause a lot of problems. Would it be
> > easier to simplify things by using an 8Mhz crystal on the BX-35 while
> > running with a divisor of 16 to communicate at 31,250 baud? And if I
> > did run at 8Mhz would I be able to use COM3 at a normal baud of 9600
> > or 2400 for an LCD?
> >
> > Thanks,
> > Justin
> >
> I found these three links which I'm sure can help you:
> http://www.embeddedrelated.com/groups/basicx/show/2615.php (BasicX
> group message 2615)
>
http://ccrma.stanford.edu/~sbacker/docs/MIDIProjectFinalDocumentation.doc
> http://www.google.com/search?hl=en&q=basicx+midi&btnG=Google+Search
>
> Regards,
> Mike




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Justin wrote:

> Cool, that solves the 8Mhz problem. Now, at 8Mhz would the chip's
> timing for 2400 baud on com3 be off? Or would it know how to compensate?
>
Well you can either find the answer in the 8535 documentation or run the
AVRCalc utility:
http://www.avrfreaks.net/index.php?module=FreaksTools&func=viewItem&item_type=tool&item_id=292

The answer is that with 8MHz, 2400 Baud is 0.16% off.

Mike





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> ... with 8MHz, 2400 Baud is 0.16% off.

Who has significantly overclocked a BasicX part?

There are a few mentions of attempts in the archive but, naturally, no
follow-up; one suggested he was running a BX-24 at 10MHz, a ~35%
speedup, about the same as the BX-24p (which gets it's speed from the
ATMega8535 over the AT90S8535.

Comm clocking is an obvious obstacle to just cranking it up; thought is
required first, and crystal switching between development and in-situ
might be needed. Anyone pushing the envelopes? Tom
Tom Becker
--... ...--
GTBecker@GTBe... www.RighTime.com
The RighTime Clock Company, Inc., Cape Coral, Florida USA
+1239 540 5700



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--- In basicx@basi..., "Tom Becker" <gtbecker@r...> wrote:
> [...] about the same as the BX-24p (which gets it's speed from the
> ATMega8535 over the AT90S8535.

I suspect that a large part of the speed increase is due to doubling
the SPI clock speed for communicating with the serial EEPROM.





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Tom Becker wrote:

> > ... with 8MHz, 2400 Baud is 0.16% off.
>
> Who has significantly overclocked a BasicX part?

Just a reminder Tom that the original reason for running the BX-35 at
8MHz instead of the usual 7.3727MHz is to get an exact baud rate of
31250 that is required for Midi.

I just so happened to have socketed the crystal on my BX-35/AVR
development board so I tried a few very quick tests. 4MHz worked fine
and 16MHz didn't work at all. I don't have 8 or 10Mhz crystals on hand
to try.

Mike
http://home.austin.rr.com/perks/basicx/Projects/





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> ... 31250...

Yes, FWIW, the MIDI baud rate is 1MHz/32= 31.25KHz, which might help
demystify its generation.

> ... don't have 8 or 10Mhz crystals on hand...

You probably do in your collection of ISA, EISA and VESA cards, or in
that old VCR, but a stable signal generator into XTAL1 would be more
flexible than arbitrary crystals. We did this with an 8085-8 25 years
ago. It wasn't necessary to remove the crystal, in fact, since its
load-side impedance (and, thus, its signal) is easily swamped by a
stiffer 1v external RF source. Of an 8MHz production batch, maybe 50%
could do 12MHz reliably.

I've just never tried it with a BX-24. Tom
Tom Becker
--... ...--
GTBecker@GTBe... www.RighTime.com
The RighTime Clock Company, Inc., Cape Coral, Florida USA
+1239 540 5700



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I need another slip ring to get a signal to a rotating platform; I
currently use my three true slip ring channels for +12v, 0v and a signal
from the platform.

I am tempted to use the motor shaft and bearing, from which the platform
hangs, as the +12v path (at maybe 50mA) to free up a ring. +12v is
regulated on the platform; I expect I might have to add some regulator
input capacitance to hold over through bearing noise.

Eventually the design will be ringless but for now, is it sound to run
low current through a steel shaft and porous bronze bearing? Tom
Tom Becker
--... ...--
GTBecker@GTBe... www.RighTime.com
The RighTime Clock Company, Inc., Cape Coral, Florida USA
+1239 540 5700



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Tom, as you know in this case, speed ratings are typically based on a
production run. Not the semiconductor physics. I would say 'go fer
it' if this is not going to be a commercial product. I know from
the 'PIC world' we can push the chips though I've not had a need to
go beyond 20MHz. As you mentioned, you will have to tweek timing-
related instructions and registers.

- Tom

--- In basicx@basi..., "Tom Becker" <gtbecker@r...> wrote:
> > ... with 8MHz, 2400 Baud is 0.16% off.
>
> Who has significantly overclocked a BasicX part?
>
> There are a few mentions of attempts in the archive but, naturally,
no
> follow-up; one suggested he was running a BX-24 at 10MHz, a ~35%
> speedup, about the same as the BX-24p (which gets it's speed from
the
> ATMega8535 over the AT90S8535.
>
> Comm clocking is an obvious obstacle to just cranking it up;
thought is
> required first, and crystal switching between development and in-
situ
> might be needed. Anyone pushing the envelopes? > Tom >
> Tom Becker
> --... ...--
> GTBecker@R... www.RighTime.com
> The RighTime Clock Company, Inc., Cape Coral, Florida USA
> +1239 540 5700




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TOM,

WHAT IS THE 3RD CONTACT SLIP RING SIGNAL. IF YOU NEED MORE SIGNAL PATHS THEN
HOW ABOUT MULIPLEXING THE DATA SERIALY AND PARALLEL IN AND OUT.

PUT A HIGH SPEED MICRO ABOVE THE SLIP RINGS AND TALK HIGH SPEED 2 WAYS.

ALSO HOW ABOUT PUTTING A BATTERY (OR A BANK OF SUPPER CAPS) ON THE PLATFORM
AND SWITCH BETWEEN CHARGING THE BATTERY (TO SUPPLY POWER FOR THE ELECTRONICS)
AND 2 WAY COMMUNICATIONS ON THAT RING ALSO.

73
SPENCE
K4KEP




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> ... SWITCH BETWEEN CHARGING THE BATTERY (TO SUPPLY POWER FOR THE
ELECTRONICS) AND 2 WAY COMMUNICATIONS...

Multiplexed power; hmmm. I've done modulated power (AC signal on DC
power), but I've never chopped DC power to make temporal space for data.

For this app it would have to be relatively fast since I deliver and
receive real time data with ~400uS resolution. That'd mean switching
the line at ~5KHz and using 100uS periods for 48 bits of bidirectional
data (32 one way, 16 bits the other way) with guard periods, so the data
would need to be faster than 480Kb/S, probably ~1Mb/S. Dropouts due to
slip ring noise could be many bits wide so, I think, the data would need
to be either self-correcting or use CRC-Ack/Nak (either would need more
data), and maybe self-clocking data.

For a temporary fix that's more than I want to take on, Spence, but the
concept is interesting. Perhaps I should just take the leap now and
move the platform data to Bluetooth, where it will be eventually anyway.

There is, BTW, lots of literature on running current through ball and
roller bearings, which causes micropitting when arcs penetrate the
lubricant, ultimately causing bearing failure. I found no information
about cylindrical bearings, though, which expose much greater contact
surface areas. Still, the theory is the same so, I suppose, they will
suffer, too.

73 Tom
Tom Becker
--... ...--
GTBecker@GTBe... www.RighTime.com
The RighTime Clock Company, Inc., Cape Coral, Florida USA
+1239 540 5700



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TOM,

THINK ABOUT IT. THAT IS BASICALLY THE WAY THAT THE DALLAS ONE WIRE DEVICES WORK.

IF YOU HAVE 3 RINGS (GROUND,BATTERY,COMM). USE THE 3RD RING FOR 2 WAY
COMMUNICATIONS. SAY RS-232. VOLTAGE WITHOUT CURRENT, OR VERY LOW CURRENT
SHOULD NOT CAUSE ANY PITTING IN THE SLIP RINGS. ALSO BY USING RS-232 IT SHOULD
REDUCE THE BACKGROUND NOISE. USE MORE THAN ONE WIPER PER RING TO ELIMINATE
CONTACT BOUNCE. I HAVE SEEN SLIP RINGS USING 5 TO 10 WIPERS PER RING. THAT
SHOULD ELIMINATE NOISE ALTOGETHER.

73
SPENCE
K4KEP





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