building a 555 hysteretic osillator

Thread Starter

hillshaveeyes57

Joined Sep 12, 2012
16
trying to build my first 555 hy. oscillator. used these instructions online: http://www.allaboutcircuits.com/vol_6/chpt_8/3.html but there were some errors i think. i see where one capacitor goes, but not the second. also the pentometer and one of the resistors seem to be mislabeled, so i really don't know where one of the resistors go.

does anyone know of a better diagram or something? i'm on breadboard, no soldering if that helps.

Thanks.
 

Wendy

Joined Mar 24, 2008
23,408
You got me, the part list does not jive with the two schematics nor the picture. The three illustrations are consistent with each other, it is the parts list that is off, R3 and R4 are swapped on it.

I made the article many years ago. I'll enter it into the corrections log. I am also moving this into the Feedback and Suggestions forum.

As for the other C1, reading is your friend. This is explained in the paragraph, it is an alternate part to vary the frequency.

This circuit has a lower end frequency of 0.7 Hertz, which means each LED will alternate and be lit for just under a second each. As you turn the potentiometer counterclockwise the frequency will increase, going well into the high end audio range. You can verify this with the Audio Detector (Vol. VI, Chapter 3, Section 12) or a piezoelectric speaker, as you continue to turn the potentiometer the pitch of the sound will rise. You can increase the frequency 100 times by replacing the capacitor with the 1µF capacitor, which will also raise the maximum frequency well into the ultrasonic range, around 70Khz.
 
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Wendy

Joined Mar 24, 2008
23,408
PARTS AND MATERIALS

  • One 9V Battery
  • Battery Clip (Radio Shack catalog # 270-325)
  • Mini Hook Clips (soldered to Battery Clip, Radio Shack catalog # 270-372)
  • U1 - 555 timer IC (Radio Shack catalog # 276-1723)
  • D1 - Red light-emitting diode (Radio Shack catalog # 276-041 or equivalent)
  • D2 - Green light-emitting diode (Radio Shack catalog # 276-022 or equivalent)
  • R1,R2 - 1 KΩ 1/4W Resistors
  • R3 - 10 Ω 1/4W Resistor
  • R4 - 10 KΩ, 15-Turn Potentiometer (Radio Shack catalog # 271-343)
  • C1 - 1 µF Capacitor (Radio Shack catalog 272-1434 or equivalent)
  • C1 - 100 µF Capacitor (Radio Shack catalog 272-1028 or equivalent)
R3 and R4 has been changed.

Thank you for pointing it out.
 
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Thread Starter

hillshaveeyes57

Joined Sep 12, 2012
16
i'm still having some trouble with it. i've built it a few times and what i'm getting now is both LEDs light up and stay that way and don't react to the pentometer in the circuit. it's like the pentometer isn't even there which makes me think either something is fried or the wiring doesn't work. i've tried turning the pentometer but the LEDs don't react. they just stay lit up, no oscillation.

i'm def. a novice at this and really just want to get the thing oscillating. i understand a little from high school physics and know that electricity flows like water in the circuit. i do want to read more into this but really just want to get it working right now.

is there another way i can wire it or is there another diagram i could use? is it possible i got some dud parts? i'll replace the oscillator and the 555 in the meantime.

thanks for the help!
 

Wendy

Joined Mar 24, 2008
23,408
The schematic and layout works, it was verified. Please start another thread about this problem, as this forum is for feedback and corrections only.

You either have a wiring error or a bad 555 (could it be a CMOS 555 like a TLC555?). Post pictures of the breadboard on the new thread.
 
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