Low Budget Low Frequency Oscillator

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A simple and cheap square-wave LFO based on the 555 timer IC

A low-cost LFO that is particularily suitable to trigger envelope generators or to provide a clock signal for (drum) sequencers and pattern generators. The circuit is so simple that you probably already have most of the parts needed. The total cost of this build was about 1 euro.

The circuit is based on this 555 Timer Astable Mode circuit. I added a 100 Ohm resistor in series with the potmeter to avoid resistance dropping to zero because this would stop the 555 from oscillating. A LED was added as visual tempo indicator and because no project is complete without at least one blinkenlight!

  • Final Revision

    Mark06/17/2016 at 17:49 0 comments

    My breadboard experiments seemed to suggest that it's OK to leave pin 5 of the venerable NE555 floating but it really isn't. The circuit becomes a bit too unstable that way. So I fixed it by adding a 0.01uF cap between pin 5 and GND. I've revised the schematic and PCB layout in the image gallery

  • Building

    Mark06/14/2016 at 18:19 0 comments

    First attempt at building this module has failed... the first PCB layout was a bit too cramped and i messed it up. Back to the drawing board!

    Second attempt: another failure. The revised layout still contained a huge wiring error but after fixing that, i'm still not getting any oscillation. So frustrating! Did i damage the 555? Very probably, because now it doesn't do a thing in a breadboard setup either.

    Ordered some new 555 chips and various other bits and they've arrived today. I will start off on the breadboard again and carefully re-evaluate my PCB design effort before i continue. Fingers crossed I'll get things working this time.

    Oops! I seriously messed up the PCB design and made some incorrect connections ( pin 2 goes to pin 6 and not 5!). Fortunately, the original 555 chip survived my blunders so now i've got a few spares in my parts drawer. All is well that ends well?

    Anyway, I've found an even simpler version of the schematic and am using that as the basis for a new board design. To be continued...

    Third time lucky! I tried my hardest to mess it all up again with my limited soldering skills but I've managed to turn the revised board layout into a functional LFO module. The resistors and capacitor I've picked produce a frequency range from approx. 0.3 Hz to 32 Hz. That's about perfect for clocking sequencers and the like.

    Thinking about adding a slower LFO with squarewave and sawtooth outputs that would be more suitable for pitch or filter modulation.

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