PWM variable frequency to Analog Voltage

[ValGurdis]

Hi.
I need to convert a PWM signal with variable frequency and 50% duty cycle, to Analog Voltage. How can I do it? Are there any ICs for this?
Thanks

 

[betwixt]

Are you asking for a frequency to voltage converter or a PWM to voltage converter?
PWM implies the pulse width can vary so perhaps what you are referring to is a square wave.
Techniques for F to V and PWM to V conversion are quite different.

Brian.

 

[ValGurdis]

Hi Brian,

thanks for response.
You are right, it is a square wave.
Basically I have a fan to control that has a tacho output which is a square wave and the frequency of it is proportional to the speed of the fan.
I need to read this output as an analog voltage as all I have available for this is an analog input on my controller.
The frequency of the tacho signal goes up to 700 or 800Hz.

thanks

 

[FvM]

Besides using a dedicated f/V converter IC, you can use a monoflop or an equivalent circuit that generates a pulse of constant width for a tacho pulse and filter the pulses to a DC voltage.

 

[danadakk]

https://www.ti.com/lit/ds/symlink/lm2907-n.pdf?ts=1633479792043&ref_url=https%253A%252F%252Fwww.google.com%252F

Or use ATTINY85 and add small amount of code to translate freq to PWM duty cycle,
and then filter that to get DC value for freq.

FreqCount Library, for Measuring Frequencies in the 1 kHz to 5 MHz Range

www.pjrc.com

One possibility


Regards, Dana.

 

[Easy peasy]

You can also do this with an asymmetrical RC filter, if you differentiate the square wave first,

i.e. put it thru a series RC ( or just C ) with an R to gnd, this gives a spike for every edge, then:

through a fast signal diode and an R to charge up a cap, C2, and a larger R across the cap, C2 to more slowly discharge C2, you can then post filter this with a smaller RC filter if you wish - not always necessary,

as the freq goes up the impulses per second to the filter go up giving a higher ave o/p voltage.

 

[ValGurdis]

Hi,

thanks to all for your answers.
I think f to V IC will be the solution.
As I have two fans to control, are there any dual channels f/V IC?
Any particular suggestions?

 

[KlausST]

Hi,

You may do an internet search, or do a search at electronics distributors (this is what I'd do).

Depending on how you want to measure and process the information ... maybe you may use a single f/V converter with a MUX at the input.

Klaus