where to apply pot to oscillator

Discussion in 'General Electronics Chat' started by 3dchipmaker, Jul 18, 2006.

  1. 3dchipmaker

    Thread Starter Member

    Jul 15, 2006
    23
    0
    where can i apply pot to following schematic to control pulse rate? and also led to tell if circuit is working?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,This circuit is a very old design. You could substitute tubes for the transistors (doubtless 2N706) and get it to work.When TR2 goes into conduction, the voltage between R2 and C1 goes down. C1 also pulls some voltage off the collector of TR1, and pulls it off. When TR2's base goes low enough, it shuts off. Meanwhile, the charge on C2 has risen, and TR1 turns on, pulling down the voltage across C2 and sending a negative pulse to point Y. There are no connector dots to be sure, but there is probably a connection with C2 and R4. The pulse out will also drop TR2's collector voltage and make sure it is off. That will let the voltage on C1 rise again to repeat the oscillation.This is a hard circuit to control, because the resistor values are very high, and have to stay high for the oscillator to work. Adding some resistance to R2 will vary the rate of oscillation, but making C1 variable might be a better way to go. The capacitors are probably a couple of hundred picofarads, or less. Neither transistor draws enough current to run a led. R1 and R4 are probably 68 - 100K. You would need to put another transistor (with a suitable base resistor) at point Y to run an indicator led. This oscillator probably runs above 50 Khz, though, so you will only see a glow. You will need an oscilloscope to watch this thing work.
     
  3. 3dchipmaker

    Thread Starter Member

    Jul 15, 2006
    23
    0
    beenthere,

    thanks for your help do you know of a schematic with resistors and transistors capicitors.something i can understand.that will get me close to 12v
    ouput with 30 pulses per second or close that i can modulate with a pot
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    For something a bit more modern, get the data sheet for an LM555 timer. Set it up as an astable oscillator. The timing nomogram should get your resistor and capacitor values pretty close for 30 Hz. Making the resistance from +12 to pin 7 somewhat variable will give you your frequency trim.
     
  5. 3dchipmaker

    Thread Starter Member

    Jul 15, 2006
    23
    0
    thanks again,
    what is the difference between ka555 and lm555 i looked and could see no difference
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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  7. 3dchipmaker

    Thread Starter Member

    Jul 15, 2006
    23
    0
    thanks all,
    i have a machine shop i program,do 3d solid modeling, geometric tolerancing and a host of other jobs that go with manufacturing.
    i ran across a project that sparked my interest in electronics. i thought how hard could it be the basics i mean. man was i in for a suprise. this experience has humbled me and gave me a greater appreciation for those involved in electronics and thier application.
    thank you all for your time and patience
     
  8. 3dchipmaker

    Thread Starter Member

    Jul 15, 2006
    23
    0
    thanks for all your help i guess we are done here please close and make room for someone else
     
  9. tony lee

    New Member

    Jul 24, 2006
    4
    0
    adjust R2 FOR # CLK
    R1/R2 DUTY CYCLE

    SEE ATTCH.DOC FOR SCHEMATIC & DATA PLOT
     
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