Control DC Motor Speed using Astable - Mike's Project

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Discussion Overview

The discussion revolves around controlling the speed of a DC motor using an astable circuit, specifically focusing on methods to vary the frequency of the astable oscillator. Participants explore different approaches, including the use of MOSFETs and alternative components.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Mike proposes using a MOSFET as a voltage-controlled resistor to change the speed of the astable circuit but expresses difficulty in getting this to work.
  • One participant defines an astable as an oscillator that generates continuous pulses and suggests its common use in timing circuits.
  • Another participant explains that an astable produces a periodic waveform and contrasts it with monostable and bistable configurations.
  • A suggestion is made to use a microcontroller's PWM generation feature for speed control, along with the option of a digital potentiometer, albeit noting the complexity of cascading comparators for control.
  • Mike expresses a preference for exploring other ideas while acknowledging the suggestions provided.

Areas of Agreement / Disagreement

The discussion contains multiple competing views regarding the best method to control the speed of the DC motor, with no consensus reached on a single approach.

Contextual Notes

Participants have not fully explored the limitations of the proposed methods, such as the specific requirements for using MOSFETs or the feasibility of implementing PWM with a microcontroller.

madmike159
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I am making a project to control the speed of a DC motor using an astable. I need to be able to change the speed of an astable (555, or one made from gate) using about 8 different voltages.

The only way I can think to do this is with a MOSFET was a voltage controlled resistor, but no one can ever get these to work.

Can anyone think of another way of varing the astable's speed or a way to implement the MOSFET?

Thanks :biggrin:
Mike
 
Last edited:
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Call me stupid but what's an "astable"?
 
Its also known as an oscillator, it creates continuous pulses at a set speed. It is often used in timing circuits.
 
Topher925 said:
Call me stupid but what's an "astable"?

That means that you're getting a periodic waveform (e.g. a square wave for a clock) instead of a single pulse (monostable) or toggling the state (bistable)

As for the original post, if you're using a microcontroller for this, you're better off using the PWM generation feature. You can also use a digital potentiometer, but these are usually digitally controlled. Unless you want to start cascading comparators to control a parallel-input digital pot.
 
No I think I'll stick with my VCR. I will look into the other ideas though, thanks for the help.

If anyone has any more ideas it would be much appreciated.
 

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