Help in Oscillator designing

Discussion in 'General Electronics Chat' started by robertbagundol, Jul 21, 2014.

  1. robertbagundol

    Thread Starter New Member

    Jul 21, 2014
    Hello! I'm actually new here but I'm really really desperate for help. So there was this class project of ours which is to simulate and make a hardware of an oscillator that produces 3 waveforms: namely sine wave, square wave, and triangular wave. But here's the twist; we need to have variables of amplitude, frequency, and duty cycle which I don't have any idea how.

    Also, we need TTL implementations and we only be using positive DC supply (like 9 volts), because having negative supply is hard for hardware implementation.

    I started out with my square wave using this schematic ( It produced a quite pretty square wave, but I don't have any idea on how to insert those 3 variables in this circuit though and it uses 12 V as the DC source.

    Can someone help me with this one please? I need some enlightenment as to how will this be done :)

    Thank you so much!
  2. to3metalcan


    Jul 20, 2014
    Looks like this circuit would run fine on 9V, but you're building most of an op-amp out of discrete parts--does the project specify that you have to use individual transistors? Either way, there's a couple of sub-circuits you need to look up...Integrators can be used effectively to convert a a square wave to a triangle. Diode wave-shapers (or just filtering and re-amplification) can turn a triangle into a pretty good sine. A comparator will turn either of the two "softer" wave forms back into a hard square, etc. etc. These bits of circuitry, whether op-amp or discrete, are all over the web.

    The quick-and-dirty way to control duty cycle is to run a square-wave through a simple variable high-pass filter and then run the result through a comparator...amplitude can, at worst, just be controlled by a potentiometer at the output. There's a resistor on your schematic labeled "Freq" that appears to set the current into all those current-mirrors...try making it a variable resistor, and I betcha it changes the frequency!
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    That circuit is unnecessarily complicated for your purpose. There are much simpler circuits for generating square waves. Try googling for 'TTL square wave generator'.
    TTL uses 5V (or by 'TTL' do you mean 74HCT?)
    Last edited: Jul 21, 2014
  4. shteii01

    AAC Fanatic!

    Feb 19, 2010
  5. ronv

    AAC Fanatic!

    Nov 12, 2008