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Building a function generator

  1. Apr 16, 2012 #1
    I am trying to build a function generator and I am unsure of how to build a circuit to vary frequency. Would I use a MOSFET? Can someone help me?
  2. jcsd
  3. Apr 16, 2012 #2
    Use a NE555 astable timer. See http://www.doctronics.co.uk/555.htm#astable [Broken]. If you need to keep the same duty cycle as you vary the frequency, then varying the capacitor is best. If you want a 50% duty cycle, then divide the NE555 output by 2 with a 7474 D-type flip flop, which would then permit varying a resistor to vary frequency.
    Last edited by a moderator: May 5, 2017
  4. Apr 16, 2012 #3


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    There is an old function generator chip, called an Intersil ICL 8038. They are rare in Electronics stores, but Ebay sites have a few of them.

    Here is a source of them:

    These can provide sine, triangle and square wave output over the audio range and above.

    Google for circuits of these chips.
    Here is one:

    They are relatively simple to use but they need a power source with positive and negative voltages.

    And you would need some way of calibrating it so that you would know what frequency was being generated. Look for a circuit with a digital display.
  5. Apr 17, 2012 #4
    They also make direct digitial synthesization chips. I know maxim makes one. I think this method is filling the space where analog waveform chips have begun to be obsolete or at least to not be manufactured anymore.


    You would most likely want to use it with a microcontroller, since they can be configured over serial links like a uart, i2c, or spi.
  6. Apr 17, 2012 #5
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