I'm looking to create a sound generator with only simple ICs and components. I believe the 555 timer IC is a good candidate to be at the core of it, but I cannot for the life of me find out how best to control frequency and PWM digitally, and without complex devices like digital potentiometers. I've tried working with different configurations of ladder networks, but nothing is giving me the results I need. Could someone more knowledgeable than me with 555 timers and simpler component networks (i'm far too used to my fancy digital stuff, ha) help me out on this one? I'd like to get a square wave frequency out with 10-90% variable duty cycle and frequency from around 50 to a few thousand hertz. Would appreciate any help from a veteran in this stuff to point me the right way. Thanks!

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    \$\begingroup\$ 555 is the wrong component to use. Duty cycle only easily adjusts 55-95%. To sweep frequency over your range, you will need to switch capacitors, not just voltages or resistors. I'm curious, why do you believe it's a good IC to use for the job, when it's clearly so unsuited to your specifications? \$\endgroup\$
    – Neil_UK
    Commented Apr 16, 2019 at 5:22
  • \$\begingroup\$ Reading the first half of that I was thinking, this is way too difficult an intro project. Reading your actual requirements, yeah, a 555 or 2 can do that. Controlling it digitally though... Yeah probably digipots or something. 0-100% duty cycle requires extra diodes, and for variable frequency and duty cycle, use a 555 as a clock triggering a second 555 one shot. There are probably much better timer ICs though, especially if you want digital control. Setting it up controlled by an actual pair of potentiometers would be much easier though. \$\endgroup\$
    – K H
    Commented Apr 16, 2019 at 5:24
  • \$\begingroup\$ How do you intend to access and control the frequency and duty cycle of this circuit? What are you using for each? Or do you intend to design and build a different circuit for each permutation? \$\endgroup\$
    – jonk
    Commented Apr 16, 2019 at 5:30

1 Answer 1


I think tryng to have an accurate digital control for a 555 oscillator output is much harder than forgetting the 555 and just using accurate digital control to generate the wanted waveform itself. A microcontroller would be a simple IC to do that, as they can have multiple PWM modules built-in.


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