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Getting into Digital circuits

Discussion in 'Electronic Basics' started by Chris W, Feb 15, 2005.

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  1. Chris W

    Chris W Guest

    I would like to get back into electronics to build some projects. Back
    many moons ago in HS I did some stuff with electronics simple stuff with
    555 timers and things. I'm hoping I can find someone that is familiar
    with building digital circuits that could use some help programming,
    there's nothing I do better than programming. Let me describe the
    project I have in mind now so I can get some input on what I need to buy
    to get started.

    I would like to be able to use a microprocessor of some kind that I can
    program via RS232, that will turn on or off a large number of lights. I
    was thinking I could have the processor output the number of the light
    it wanted, and if it wanted to turn on or off. Maybe it would just
    toggle the light, so every time a lights number came up, it would just
    alternate it between on and off. My first project will have about 30
    lights, but I would like the design to be expandable. Since an 8 bit
    number gives us 256, I was thinking that would be the limit. Maybe have
    modules that will control a group of, say 8 lights, that can plug into
    the output of the processor, then another module can plug into the
    previous one. . . For now the lights are just going to be 20mW LEDs,
    but I have plans for projects that will need either around 5W lights, or
    gangs of 10 to 20 LEDs. So I will need some kind of relay, I guess a
    solid state relay of some kind would be best. As I glance through my
    mouser catalog I see several different programmable controllers that
    look like they would work for something like this, but I have no idea
    which one to use. Thanks in advance for any suggestions.

    If this isn't the best NG for this please let me know which one is.
    There seem to be a lot of electronics NGs.

    Also I recently purchased a few prototype boards on ebay and one came
    with several IC chips and things. Where is a good reference that will
    tell me what they all are and what they do? Back in HS we had a
    reference book that told all about various common IC chips and gave some
    sample circuits. Surely these days there is some on line reference like
    that.

    --
    Chris W

    Gift Giving Made Easy
    Get the gifts you want &
    give the gifts they want
    http://thewishzone.com

    "They that can give up essential liberty
    to obtain a little temporary safety
    deserve neither liberty nor safety."
    -- Benjamin Franklin, 1759 Historical Review of Pennsylvania
     
  2. loedown

    loedown Guest

    These sort of applications are ideal for PIC chips, simple to use, require
    almost no auxilliary circuitry, and are easy to program. Very steep learning
    curve, and the programmer will set you back somewhere in the order of $200
    AUD, but the PIC 18F672 has provision for RS232 and multiple outputs (22).

    Paul
     
  3. Ruediger

    Ruediger Guest

    Even better: Most PIC's can be programmed over their In-System-Programming
    ports, and all it needs is a simple circuit; the manufacturer,
    http://www.microchip.com
    has the DIY-programmer somewhere in their application-sheets.

    The ideal multipurpose workhorse that I fell in love with is the PIC16F88, a
    little beast we are now using in a wearable device we develop at the
    University. My greates flaw is, I'm lousy at rogrmming, my skill is
    designig circuitry.

    I have an idea for a very cheap, but highly versatile wearable device in my
    head, but I would need to first develop the circuitry and look for the
    parts and their costs ( it should be a device priced about 30$, requiring a
    PeeCee somewhere, connecting to it by wireless. ). That baby would need
    some good amount of programming, especially on the PC's side, where a lot
    of outputs would need to be redirected, requiring, hum... sorta like a
    X-driver for the parallel port ;)

    Anyway.

    My PIC of choice for multipurpose -USage is the PIC 16F88. 2*8Bit-Ports, so
    lotsa outputs.
     
  4. Chris W

    Chris W Guest

    What about something like the RABBIT Microprocessor modules? Wouldn't
    that be the easy way? Could I program something like that in C?

    Also does someone make some kind of IC chip that takes say 3 bit binary
    number for input on 3 pins and then makes one of 8 output pins go high
    based on the input binary number?


    --
    Chris W

    Gift Giving Made Easy
    Get the gifts you want &
    give the gifts they want
    http://thewishzone.com

    "They that can give up essential liberty
    to obtain a little temporary safety
    deserve neither liberty nor safety."
    -- Benjamin Franklin, 1759 Historical Review of Pennsylvania
     
  5. Lord Garth

    Lord Garth Guest

    The 74HC138 is such a chip but the outputs go low based upon the input.
    You can do this function with any EPROM if you wish.
     
  6. John Fields

    John Fields Guest

     
  7. Rich Grise

    Rich Grise Guest

    Google is your friend:
    http://www.google.com/search?q=digital+electronics+basics&btnG=Search

    Have Fun!
    Rich
     
  8. Chris W

    Chris W Guest

    I also found the 238 version which is more what I want. Can you tell me
    more about how I would use and EPROM to do that and is there a 4 to 16
    line encoder too? I can't find one at Mouser.com

    --
    Chris W

    Gift Giving Made Easy
    Get the gifts you want &
    give the gifts they want
    http://thewishzone.com

    "They that can give up essential liberty
    to obtain a little temporary safety
    deserve neither liberty nor safety."
    -- Benjamin Franklin, 1759 Historical Review of Pennsylvania
     
  9. Lord Garth

    Lord Garth Guest

    Sure Chris,

    Firstly, you need to call it a decoder. Either a 3 to 8 demultiplexer /
    decoder or
    a 4 to 16 demultiplexer. The old TTL part number for this was the 74154.

    To use a EPROM for this function, you would program the output pattern to
    whatever you need for a given input pattern. The inputs go to the address
    lines,
    A3 A2 A1 A0 for 4 bits and the unused address lines are grounded.
    Don't forget to enable the EPROM with its *CS input and enable its outputs
    with the *OE input. Many need the Vpp pin set high as well.

    This is a great use for those old 2K EPROMs that often get tossed. Newer
    EPROM
    part numbers usually reflect the number of bits (not bytes) they can hold.
    A 27128
    holds 128k bits which is arranged as 16k x 8. Older EPROMs had part numbers
    like 2716. The 2716 is 2k x 8. Address range from 0000 through 1FFF, most
    of
    which will be wasted in your application but its a wasted part by most
    standards.

    Note too that you can use two '238 to form a 16 line decoder by making use
    of
    the enable inputs. The A2 A1 A0 inputs go to both 238s while A3 goes to the
    active high enable one 238 and the active low enable on the other.

    Have fun and let us know if you need an EPROM programmed.
     
  10. Chris W

    Chris W Guest

    I don't know where I encoder came from I meant to type decoder. the
    search for demultiplexer found the 4 to 16 line version at mouser.com
    Let me see if I get the idea. It sounds like the EPROMs mostly have an
    8 bit output. So for the case of turning on 1 of 8 lights, I basically
    program in 8, 8 bit numbers so I would use 8 bytes or 64 bits of memory
    from the EPROM. Are EPROMs that have 16 bit output very expensive? Or
    would I be better off using 2 with 8 bit outputs? The EPROM way sounds
    like an interesting solution. I want to have the possibility of having
    as many as 16 separate boards that each control 16 lights. So I could
    program the EPROM(S) on each board to respond to 8 bit binary inputs
    like so..

    Board 1 responds to 0 to 15
    Board 2 responds to 16 to 31
    Board 3 responds to 32 to 47
    .. . .
    Board 16 responds to 240 to 255

    I like that!

    Now for a few questions. Would an 8 bit output from a PIC have a
    problem driving as many as 16 of these circuits hooked in parallel? My
    first application is going to drive a single high intensity white LED on
    each of the possible 256 output lines. I believe they draw around 20mA
    at about 3.5V, will I need some kind of driver or will the circuit
    handle enough power to drive all 16 lights on each board at a time?
    Finally how to turn on or off each LED, and leave them in that state
    till the next signal. Would a flip flop would be the way to go? Some
    way to tell it to turn off or on might be nice, that way I wouldn't have
    to keep as close a track to which lights were on and which were off.

    --
    Chris W

    Gift Giving Made Easy
    Get the gifts you want &
    give the gifts they want
    http://thewishzone.com

    "They that can give up essential liberty
    to obtain a little temporary safety
    deserve neither liberty nor safety."
    -- Benjamin Franklin, 1759 Historical Review of Pennsylvania
     
  11. Lord Garth

    Lord Garth Guest

    I would never allow the PIC to drive the lamps directly, I'd buffer the
    outputs
    in one of several ways.

    The EPROM is always used in a minimum of a byte so excepting for the part
    number, there is no need to concern yourself about the number of bits you
    have
    used. 16 bit EPROMs are more expensive and few cheap programmers can use
    handle them, better to use two 8 bit device and some very easy control logic
    as described for dual 238s. You can also look into multiplexing the outputs
    to accomplish your goal.

    Maxim has an IC that, in one mode of operation, can address as many as 64
    separate lamps. I do not recall its part number but this chip might well be
    worth your time to investigate.

    I need to run, I have work to do.....
     
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