What's the easiest way to generate a square/rectangular wave using a simple circuit? It will be used to pulse a motor, and I need to be able to alter the duty cycle of the rectangular waveform from 5% to 95% using a potentiometer, where duty cycle ∝ voltage. My power supply is 3.3V, so I'm limited to BJTs for transistors. Any suggestions?

Edit 1: Most of my attempts have been starting with an RC circuit and trying to use BJTs to set the output high when the cap is charged, which causes the cap to discharge and start again, or something along those lines.

Edit 2: A 555 timer wouldn't allow me to have the duty cycle directly proportional to the voltage on the pot.

Edit 3: In the end I decided on a LTC6992 PWM IC, as it provides the most accuracy, and doesn't take up much space.


closed as too broad by Marcus Müller, DerStrom8, MCG, Andy aka, brhans May 30 '18 at 14:59

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Plenty! Ring oscillators, crystal oscillators spring to mind. Also, the (obnoxiously) prevalent NE555... \$\endgroup\$ – Marcus Müller May 30 '18 at 14:42
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    \$\begingroup\$ What frequency do you want ? A multivibrator or logic gate + RC oscillator sould be easy to implement. \$\endgroup\$ – Long Pham May 30 '18 at 14:43
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    \$\begingroup\$ Also, sounds a lot like the easiest way to implement this would be a microcontroller with a proper PWM unit \$\endgroup\$ – Marcus Müller May 30 '18 at 14:44
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    \$\begingroup\$ So, considering there's a lot of things that you could've done (and I'm really not sure where the idea you'd need to have an inductor in there comes from), I'm voting to close this as too broad. Maybe you could explain what you've considered (you mention you did consider alternatives, but don't mention any of these), to remedy that fact? \$\endgroup\$ – Marcus Müller May 30 '18 at 14:46
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    \$\begingroup\$ I'm quite shocked your "trying lots of things with no success" didn't turn up solutions. There are countless options out there, and if you'd done any real searching it would have been very easy to find them. \$\endgroup\$ – DerStrom8 May 30 '18 at 14:48

Any ideas?

enter image description here

Choose the device that has 0% to 100% duty cycle coverage.

Is it possible to generate a square/rectangular wave ... with no inductors?

Of course.

One example of many possible ones is a Schmitt trigger inverter with its input tied to its output. You can add a RC filter from output to input to make the frequency more predictable (but also lower).

Another example is the common two-transistor multivibrator. Look it up.

Then there are ICs like the infamous 666 555 timer.

If you are actually after variable-duty cycle PWM, then the simplest way to produce that is with a microcontroller that is already in your system. Most microcontrollers have PWM generators built in. Even if yours doesn't, it's usually easy to upgrade to one that does within a family.


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