Triangle Wave Generator

Discussion in 'The Projects Forum' started by rueffy, Jun 29, 2013.

  1. rueffy

    Thread Starter Member

    Jun 29, 2013
    39
    3
    Hi All,

    I am in the process of designing a PWM comms system that drives a LASER light with the receiver being an LDR circuit some distance away. I am having a bit of trouble getting a reliable triangle wave output from an oscillator circuit that I am using.

    The circuit

    [​IMG]

    The formula

    Screen Shot 2013-06-30 at 11.00.56 AM.jpg

    My circuit interface requirements are thus,

    The final PWM output must have a 3vp-p output to conform to the LASER operating voltage. The Triangle Wave must be around 10kHz in frequency, this meets the requirement of the reference wave being at least double the highest frequency of the information (3400Hz for voice). I'm not sure what the Vpp requirements of the triangle wave should be in order to match this circuit. I'm not sure if its even relevant, it will be summed with the modulation waveform using a circuit I am yet to determine (perhaps a simple resistive network using DC blocking capacitor at output of oscillator).

    Basically, the problem I am having is choosing appropriate resistance and capacitance values. I have achieved a 12kHz output on a breadboard but the triangle wave is distorted during the negative going ramp. I am not set on this circuit so if you know of any alternatives that are simpler please suggest them.

    Any advice appreciated.

    Cheers,
    Rueffy.
     
  2. rueffy

    Thread Starter Member

    Jun 29, 2013
    39
    3
    I should also mention I am using a VCC of 9V
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,429
    3,360
    We can't help you if we don't know your part numbers and values.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,997
    3,754
    Which op amp are you using? The circuit is designed for a split power supply. If using a 9 volt battery, you will need a buffered virtual ground at 1/2Vcc.
     
  5. rueffy

    Thread Starter Member

    Jun 29, 2013
    39
    3
    Using 741 op-amps, as for R and C values that's what my question was regarding. Was considering running of a 9v battery - can you please explain the buffered virtual ground concept or alternatively is there another circuit that utilises single-rail op-amps?
     
  6. Shagas

    Active Member

    May 13, 2013
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  7. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    The 741 opamp is not a single supply opamp. besides being VERY outdated. The simple solution. Add another 9 volt supply for negetive power supply. +/- 9 volt is a good supply voltage for the 741 type opamp
     
  8. rueffy

    Thread Starter Member

    Jun 29, 2013
    39
    3
  9. bance

    Member

    Aug 11, 2012
    315
    34
    Pretty good explanation here.

    HTH Steve.
     
  10. rueffy

    Thread Starter Member

    Jun 29, 2013
    39
    3
    Outstanding explanation...thanks bance. The clearest formula I've seen so far.
     
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