# Resolution of 555 PWM

Joined Jul 4, 2016
54
Hi everyone
I'm working on a power supply project and I found the best choice for voltage control is PWM
I have 2 choices, the Arduino and the 555 so I was wondering if the 555 has good resolution to not waste a microcontroller
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#### bertus

Joined Apr 5, 2008
19,939
Hello,

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Bertus

Joined Jul 4, 2016
54

#### AlbertHall

Joined Jun 4, 2014
8,184
One of the 1N4148 diodes should be the other way round.
The resolution of this circuit is as good as the resolution of the pot you use.
Get a good 10 or 25 turn pot and it will beat the arduino hands down.
Having said that, you're unlikely to need better resolution than you can get from the arduino (up to 16 bits if you're cunning).

#### WBahn

Joined Mar 31, 2012
24,572
One of the 1N4148 diodes should be the other way round.
The resolution of this circuit is as good as the resolution of the pot you use.
Get a good 10 or 25 turn pot and it will beat the arduino hands down.
Having said that, you're unlikely to need better resolution than you can get from the arduino (up to 16 bits if you're cunning).
A 25 turn pot is going to beat 16-bits of resolution "hands down"???

1 turn of the pot would be equivalent to over 2600 lsb's. Or, put the other way around, 1 lsb would be less than 1/7th of a degree.

#### Sensacell

Joined Jun 19, 2012
2,428
A pot, being an analog device, has theoretically infinite resolution.
Having said that- beware that some wire-wound pots actually produce finite steps, due to their internal construction.

Looking at your circuit, I see no real need for high resolution.

#### WBahn

Joined Mar 31, 2012
24,572
A pot has "theoretically infinite resolution" only on a very superficial basis. Try to turn the pot just 0.0000000000001 degree. If you achieve that, then try to turn it 1/10 of that amount. All kinds of physical effects will blow the theory out of the water long, long before you get anywhere close to even that level of resolution, and that's a long way from anything resembling infinite resoltuion. Or, to come at it another way. Position the pot at some position randomly and measure it, using whatever means is convenient, to a "high" degree of accuracy. Now turn the pot away and try to reposition it to that same position. Your measurements don't have to be all that accurate before you reach a point that you are almost never able to get it to that position and, if you try enough times, you build up a probability distribution whose standard deviation serves as a decent measure of the pot's resolution.

#### crutschow

Joined Mar 14, 2008
23,140
If you are just going to control the speed by turning a mechanical pot then use a 555.
A 10-turn pot will give you all the resolution you need.
A good Bourns wirewound 10-turn pot can have a resolution of .03% or better.

#### GopherT

Joined Nov 23, 2012
7,983
a 555 and a 25 turn pot will be better than an arduino if you want more than 2k Hz Pwm frequency. Above that, you cannot achieve more than 12 bots of resolution.

#### #12

Joined Nov 30, 2010
18,076
A pot, being an analog device, has theoretically infinite resolution.
In theory, there is no difference between theory and practice. In practice, there is.
That being said, this Mohamed probably doesn't need (12 bit resolution) 4096 definable and repeatable speeds. A ten turn pot will provide at least 100 speed settings. (What crutschow said.)