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Need a 38khz pulse, is there anything better than using a 555?

Discussion in 'Electronic Basics' started by Bob Business, Nov 17, 2003.

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  1. Bob Business

    Bob Business Guest

    Hello,
    I am working on a project that sends signals via 38khz modulated IR
    remote. I see some circuits that use a 555, but it seems very error
    prone due to tolerances, and I don't have anything to test for
    frequency. I found this chip
    http://www.rentron.com/remote_control/TX-IR.htm which is a programmed
    PIC that does exactly what I want for $6.00 plus $1.50 for resonator.
    Are there any other options, or should I not worry and use a 555,
    possible with a trimmer.
    Thanks
    BB
     
  2. CFoley1064

    CFoley1064 Guest

    Hello,
    Several manufacturers make series resonant crystals at exactly that frequency.
    Digi-Key sells the Epson C-2 38.0000KA-P as their P/N SE3314-ND for $1.35 USD.
    That, a couple of small caps, and a spare gate or two and you'll be good to go
    at a guaranteed 100 ppm tolerance.

    Good luck.
    Chris
     
  3. i would not use a 555. ever.

    go for the rentron parts, unless your goal is to learn about building
    oscillators. the cost is entirely reasonable.

    i think the apps shown in the rentron datasheet are a bit optimistic -
    if you use those schematics do not deviate from their design.

    in particular regular serial comms over IR can be a bit dicey - you want
    to look into how to format packets with some error detection and so
    forth. googling here is a good place to start.

    but the TX-IR will do exactly what it says, i bet.

    if you get interested (or sick of paying $6 a pop) you can program a PIC
    yourself. it's a long road, perhaps, but a relatively bump-free and very
    much travelled one.

    -- rob
     
  4. Bob Business

    Bob Business Guest

    Previously I was just going to connect the trigger to a transistor, to
    turn on the leds. How would I do this with a crystal?
     
  5. Bob, to drive the crystal, you need a driver circuit, which generally
    consists of an inverter IC, a couple of small caps, and a couple of
    resistors. Here is one that I've used:

    4049A 4049B

    |\ |\
    +-| >O--+--| >O- Drive LED
    | |/ | |/
    | |
    | 10M |
    |-/\/\/-+
    | |
    | .-.
    | | |R=100k
    | | |
    | _ '-'
    | | | |
    +-|| ||-+ 38kHz crystal
    | |_| |
    --- ---
    22pF --- --- 22pF
    | |
    | |
    +---+---+
    |
    ===
    GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
     
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