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Can I do this with a uProcessor?

Discussion in 'Electronic Design' started by tempus fugit, May 21, 2007.

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  1. Eeyore

    Eeyore Guest

    Use the 89S8253 (an update it seems)

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

    This programmer should be fine with it too but I'd want to be 100% sure of device support before buying.

  2. Eeyore

    Eeyore Guest

    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.

  3. Eeyore

    Eeyore Guest

    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.

  4. Electrostatic shielding can be pretty decent on a cheap 2-layer board
    if you use copper pour and housing metal effectively.
    No much magnetic coupling, it's a keyboard scan not an LED scan. The
    latter would be harder to deal with.
    It's for a *guitar*. What's the signal to noise ratio on the pickup?

    Best regards,
    Spehro Pefhany
  5. tempus fugit

    tempus fugit Guest

    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.
  6. tempus fugit

    tempus fugit Guest

    ouch that hurts...
  7. tempus fugit

    tempus fugit Guest

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

    Rich Grise Guest


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

  9. Eeyore

    Eeyore Guest

    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 ?

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

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

    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.

  10. Rich Grise

    Rich Grise Guest

    Hey, don't be too hasty to condemn - my brother plays guitar

    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. :)

  11. Eeyore

    Eeyore Guest

    Your hearing is shot.

  12. Rich Grise

    Rich Grise Guest

    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". :)

  13. Rich Grise

    Rich Grise Guest

    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

    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.


  14. 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
  15. Eeyore

    Eeyore Guest

    Who last paid you $240/hour ?

  16. You're fingering it wrong, then.

    Best regards,
    Spehro Pefhany
  17. tempus fugit

    tempus fugit Guest

  18. tempus fugit

    tempus fugit Guest

    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).

  19. tempus fugit

    tempus fugit Guest

    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.
  20. Twat say? I **** hear you!

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