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Low Voltage square wave

Discussion in 'The Projects Forum' started by NetGnome, Jul 6, 2009.

  1. NetGnome

    Thread Starter New Member

    Jul 6, 2009
    I want create a square wave pulse train output that I can vary by program between 0 and 1 volt in .1V steps. The wave should be square and be able to output 30ma from 0 to 100KHz. I have a micro controller digital output producing a 3.3V TTL pulse train that I want. I have an analog output that can produce the voltages and current I need, but it is not fast enough.

    I tried using an optocoupler connected to my TTL digital output to switch a PNP transistor that was connected to my analog ouput and pulled down by resistor to zero. This works above a 1 volt output but not below.

    What transistors/circuit will switch low enough, fast enough and carry the current I need.

  2. bertus


    Apr 5, 2008

    Did you already think of a transconductance amplifier?
    The LM13700 is one. (take a look at the datasheet).

    Here is also an example used in the analog synthesyser as a voltage controlled amplfier.

  3. millwood


    if you don't output too much current and want the voltage to be precise (and have spare pins on the mcu), you can build a dac using a few pins on the mcu through a r2r network.

    if you need more current, you can always buffer it.
  4. mik3

    Senior Member

    Feb 4, 2008
    You can but it is hard to find the exact resistor values required.
    It would be better to use a digital potentiometer. You apply a digital value at its input and it outputs an analog value.