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Single IC linear adj. pulse generator

Discussion in 'Electronic Design' started by [email protected], Sep 3, 2003.

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  1. Guest

    I need a single IC pulse generator with a range of 1-20 Hz that has a
    _linear_ frequency adjustment via a potentiometer. Duty cycle
    adjustment via trimpot would be an added advantage.

    Can anyone advise where I can find a schematic for this?

    As far as I am aware making an LM 7555 linear adjust entails
    additional active components. For design reasons, I would prefer not
    to do this, or use a dedicated function generator IC, ie. XR 2206,
    etc.

    Thanks for your response

    Peter Nielsen
     
  2. Jim Thompson

    Jim Thompson Guest

    And *why* is that? Homework problem ?:)

    ...Jim Thompson
     
  3. Ban

    Ban Guest

    Here is a nice and very linear variable duty cycle square wave oscillator,
    which will work from less than 0.01Hz to 20Hz, but with proper scaling of
    charging current and -capacitor and high speed comparator you can easily
    reach 20MHz.
    If you want a very linear adjustment, you will have to use a voltage
    controlled current source at the frequency input and a buffer at the duty
    cycle input.

    If you buffer the capacitor voltage you have a *very* linear triangle wave,
    suitable for reference use in a delta A/D.

    ciao Ban
     
  4. Ban

    Ban Guest

    see schematic below, forgot to paste it
    +-----------------+-------+----------------------o
    | .-. .-. 10V
    | 1k0| | 1k0| |
    | | | | |
    | '-' '-'
    | | |
    | >| |<
    | |-+-|
    | /| | |\
    | +---+ |
    | | | rail to rail comparator/opamp
    | | +---)-----------------+
    | frequency | | | |\ |
    .-. | | +-+ +------|-\ |
    10k | |<-------+ | | V V | | >--+--#
    | | .-. | +-+ | | +-|+/ | out
    '-' | | | | +----+ | |/ |
    | 100k| | | V V 10u| + | ___ |
    +---+ '-' | +-+ ### +-|___|-+
    | | | | 1N4148| --- | 10k
    | |/ +---+ | | | |
    +-| | | | | GND | ___
    |> \| | |/ |/ | +-|___|-VCC
    | |-+---------| | | 3k3
    GND <| |> |> | .-. duty cycle
    | | | +->| |
    .-. .-. .-. | |100k
    1k0| | 1k0| | 1k0| | '-'
    | | | | | | | ___
    '-' '-' '-' +-|___|-GND
    | | | 3k3
    GND GND GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
     
  5. Fred Bloggs

    Fred Bloggs Guest


    A very simple way is shown here- you can use a single supply 15V and
    derive the 5V by zener or some other regulation, or you can use a single
    5V and use a 2nd 555 and diode voltage tripler to derive ~15V:

    View in a fixed-width font such as Courier.




    freq adj
    15V
    | 10k 10k 10k
    +--------------/\/\---/\/\---/\/\-----+
    | /|\ |
    c | ---
    \| | gnd
    npn|--------------------+
    /|
    e
    | duty adj
    \
    1.5k 10k 10k 10k
    \ +--/\/\---/\/\---/\/\-----+
    5V / | /|\ |
    o e | | ---
    | |/ | | Vth gnd
    +-----|pnp | |
    | |\ | | 1M
    | c | +---/\/\------+
    | | | | |
    +-------|-----------+----------|---------+ |
    | | | | | comparator
    | | +--vcc---+ | | |
    | I | | +------(+)\ |
    | | | 555 | | >--+----> Pulse
    | V | | +------(-)/
    | | | | |
    +----+-----+-thresh | | | 3xI
    | | +-trig | | | Frequency= ------
    | === +-dis | | | CtxVcc
    | CT | | | |
    | 47u +-- gnd -+ | |
    | | | | | Vth
    | +------------+-------------------+ Duty= --- - 1
    | | | 1.6
    +---------------------------+ ---
    | gnd
    |
    | / / / -3.4-
    | / | / | / |
    | | / | / | / |
    +-> -+------+------+------+-----Vth-
    | / | / | / | /
    -1.6-

    - - - - -5-
    | | | | | | | |
    | | | | | | | | Pulse
    | | | | | | | |
    -+ +----+ +----+ +----+ +----0-
     
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