Can I do this with a uProcessor?

[Eeyore]

It's done by writing software to drive the micro's port pins in the required
manner.

Since you're new to all this and key scanning will in any case create an audio
tone that's very likely to break through into your signal, I very strongly
suggest you don't bother and use 1 input or output per port pin.

After all an 80C51 variant such as the 89s53
http://atmel.com/dyn/products/produ...04&family_name=8051+Architecture&part_id=1919

is inexpensive, easy to use and has 32 general purpose I/O lines anyway.

Use the 89S8253 (an update it seems)
http://uk.farnell.com/jsp/Semicondu...AT89S8253-24PU/displayProduct.jsp?sku=1095746

A mere £2.97 in 1 off from Farnell and available in a DIL package so it's easy to protoytype with for the
hobbyist.

This programmer should be fine with it too but I'd want to be 100% sure of device support before buying.
http://cgi.ebay.co.uk/NSP-Universal...875QQihZ012QQcategoryZ294QQrdZ1QQcmdZViewItem

http://cgi.ebay.co.uk/TOP2004-USB-U...699QQihZ012QQcategoryZ294QQrdZ1QQcmdZViewItem



Graham

 

[Eeyore]

No much magnetic coupling, it's a keyboard scan not an LED scan. The
latter would be harder to deal with.

True enough. The produt I had in mind had some multiplexed loads to but these did have
seperate drivers so the current involved wasn't that large. It was still problematic. I
should perhaps point out that the hardware was designed by someone else but I had to
make it work to a saleable standard.

More to the point though, the poor lad is new to the game and will be struggling on the
learning curve anyway, so why introduce additional complexity when it's *not needed* !

Packing it all into say a 16 pin SMT part is great for volume manufacture but this is
just a hobby for him.

Graham

 

[Eeyore]

It's for a *guitar*. What's the signal to noise ratio on the pickup?

You might be surprised just how good it can be.

I'm sorry but the dismissive "it's just a guitar" attitude is typical of non-audio
practicioners who think the task is trivial and is one reason none of them can design
decent quality audio to save themselves.

Tempus fugit has posted many times about his project and it's quite clear to me that
he's very sensitive indeed to little pops and clicks and the like so I expect him to be
working to a high standard of performance.

Graham

 

[Spehro Pefhany]

It was a very nice design actually but like all things in the real world was
subject to cost constraints so couldn't be on say a 4 layer board.

Electrostatic shielding can be pretty decent on a cheap 2-layer board
if you use copper pour and housing metal effectively.

Try eliminating electro-statically and electro-magnetically coupled interference

No much magnetic coupling, it's a keyboard scan not an LED scan. The
latter would be harder to deal with.

when the audio noise floor is >=110dB below the 5V typical switching voltage. Note
that to be sure of not hearing a discrete tone, the pickup into the audio will need
to be about >=130dB below 5V since single tones are not well masked by wideband
noise.

130dB. Don't forget that.

It's for a *guitar*. What's the signal to noise ratio on the pickup?

We used to agonise over the induced click you'd get from a single short trace
switching maybe just a local control voltage. It's astonishing what makes itself
known when you actually *listen* to audio, as opposed to relying on long term
averaged measurements.

Graham

Best regards,
Spehro Pefhany

 

[tempus fugit]

But what benefit do you expect to get from this ?

Graham

Well, supposedly a capacitative click can be introduced to the audio when
switching using non-mechanical switches, which in this case I suppose my
relay drivers (darlington pair transistors) technically are. Not being suire
of the limitations of the micros, I thought maybe you could just program a
ramped up voltage as the desired output.

 

[tempus fugit]

It's for a *guitar*.

ouch that hurts...

 

[tempus fugit]

Tempus fugit has posted many times about his project and it's quite clear to me that
he's very sensitive indeed to little pops and clicks and the like so I expect him to be
working to a high standard of performance.

Indeed I am, in fact that's why I'm thinking about redesigning in the 1st
place.

 

[Rich Grise]

You might be surprised just how good it can be.

I'm sorry but the dismissive "it's just a guitar" attitude is typical of non-audio
practicioners

s/practicioners/practitioners/
s/practitioners/phools/

I've found that anything below -20 dB is inaudible anyway, except for the
subliminal effects, if any.

Cheers!
Rich

 

[Eeyore]

Well, supposedly a capacitative click can be introduced to the audio when
switching using non-mechanical switches,

Like fet switches ? It's 'charge injection' usually. Jfets don't exhibit this
effect like CMOS swiches, although there is another way they can click but this
can be reduced by driving them carefully. Do you recall these were the type I
originally recommended ?

which in this case I suppose my relay drivers (darlington pair transistors)
technically are.

Absolutely not. No connection in any way whatever. Transistors themselves won't
click.

Not being suire of the limitations of the micros, I thought maybe you could
just program a ramped up voltage as the desired output.

Only if it has a D-A output but you can get a ramp of sorts with an R and a C
anyway.

Beware that relays click too, not just from the contacts opening and closing and
the effect this has on any currents but also as the result of induction from the
magnetic field from the coil. The magnetic field problem *can* be reduced by
ramping the *coil current* though.

Graham

 

[Rich Grise]

ouch that hurts...

Hey, don't be too hasty to condemn - my brother plays guitar
professionally:
http://tamarak.iwarp.com/

My lil' bro is the blond-headed one in the foreground on the CD cover.
Scroll down; he's "Dan Grise". Yes, it's true, I have a nappy-headed ho
in my family. ;-P

BTW, buy their CD, and tell them I sent you.

Cheers!
Rich

 

[Eeyore]

I've found that anything below -20 dB is inaudible anyway,

Your hearing is shot.

Graham

 

[Rich Grise]

So by 8 bits you mean a total of 8 pins to connect to (I'm still a bit
unsure of all the terminology)?

have
a bit more complexity.

This is the case, although it is possible that more than one key may get
pressed accidentally...

I once did a 64-key keyboard scanner with a 6502 - a very nice processor,
as long as you don't push its limits - and I wrote in N-key rollover,
which is really easy to do - just put them into a queue.

And it's true, keystrokes don't need much debouncing.

Of course, if you make an error, you have to correct it, usually by
"backspace".

Cheers!
Rich

 

[Rich Grise]

I understand that, but do I then need 1 input pin for each switch, and 1 for
each output? That would mean 15 ins, plus 6 outs. Since I only have 6
different parameters to control, I was wondering if there was a way to use
only 6 input pins and 6 outs, plus the 1 extra for the bank switch.

Are you not reading any responses here? People have been explaining
multiplexing for about three days now!

You need ONE output for ANY NUMBER OF ROWS OF SWITCHES, and
ONE INPUT FOR ANY NUMBER OF COLUMNS OF SWITCHES!

Activate one row, and read the state of the columns. If there is an active
input, decode it and put it into your queue. Activate the next row, and
read the state of the columns. If there is an active input, decode it, and
put it into your queue. Activate the NEXT row, read the inputs, and if
one is active, put THAT into your queue. Continue, until you've scanned
all of the rows.

I don't know how much more simply it can be explained, short of actually
doing your homework for you, and I charge $240.00/hour to do that.

Cheers!
Rich

 

[Michael A. Terrell]

You're fingering it wrong, then.

Leave him alone, Sphero. He'll finger it out, sooner or later. ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Eeyore]

I don't know how much more simply it can be explained, short of actually
doing your homework for you, and I charge $240.00/hour to do that.

Who last paid you $240/hour ?

Graham

 

[Spehro Pefhany]

ouch that hurts...

You're fingering it wrong, then.



Best regards,
Spehro Pefhany

 

[tempus fugit]

You're fingering it wrong, then.

ROFL

 

[tempus fugit]

Like fet switches ? It's 'charge injection' usually. Jfets don't exhibit this
effect like CMOS swiches, although there is another way they can click but this
can be reduced by driving them carefully. Do you recall these were the type I
originally recommended ?

I do, and I haven't ruled this out as an option, now that I'm thinking of
redoing everything anyway. When you last gave me that advice, working JFETs
that needed a negative voltage to turn off would've required a lot of
rewiring of my existing design (which is why, if I go to that trouble, I'd
like to have a simper layout).

Thanks

 

[tempus fugit]

">

Are you not reading any responses here? People have been explaining
multiplexing for about three days now!

You need ONE output for ANY NUMBER OF ROWS OF SWITCHES, and
ONE INPUT FOR ANY NUMBER OF COLUMNS OF SWITCHES!

I've read each one carefully, and some a number of times actually. Lots of
reading, but I'm still not quite understanding everything yet.

 

[Rich the Newsgroup Wacko]

Leave him alone, Sphero. He'll finger it out, sooner or later. ;-)

Twat say? I **** hear you!


Cheers!
Rich