Can anyone help me to use 4046 as frequency to voltage converter

Thread Starter

likhithablr

Joined Jan 28, 2018
1
Hello guys, I am new to AAC. I am working on a small sensor based project.
I am using a hall effect sensor (461C), which only respond to one polarity, thus producing a square wave. My supply is only a single rail 5V supply, so my square wave has amplitude of 5V. A magnet is attached horizontally to a motor and brought close to the sensor, which produces square waves of varying width according to the supply to the motor(which is between 0-3V)
Since it is a analog project, I have to convert frequency to analog dc voltage. On trying out different circuits such as peak detected, voltage doubler circuits, I was advised to use 4046 for FCV, since frequency that I get form my sensor is very small only between 0-100Hz.
Can I ask you to advice me one how to use 4046 as FCV and if possible a circuit diagram can help me.

Thank you in advance for all suggestions and help offered.
 

AlbertHall

Joined Jun 4, 2014
9,272
From figure 9c in the datasheet the maximum ratio of maximum frequency to minimum frequency is about 80 - so from 100Hz down to about 1.2Hz.
 

Alec_t

Joined Sep 17, 2013
10,902
You could use the Hall sensor to trigger a monostable circuit generating fixed-width pulses, then integrate the pulses with an RC filter.
A monostable can be made with a CD4538, for example, or with gates having an inverting function (e.g CD40106, or CD4093).
 

AlbertHall

Joined Jun 4, 2014
9,272
The LM2907 might do the job but the problem still arises at the 0Hz end of the scale. The chip generates pulses then a low pass filter smoothes the pulses into a DC level. For very low frequencies this filter would need a long response time and so the output voltage will always lag changes in the input frequency. That problem will generally apply to such circuits including post #4.
 

Alec_t

Joined Sep 17, 2013
10,902
Yes, the filter is the problem. The only way I can see of avoiding one would be to use a micro (or whatever) to measure and process the pulse period.
 

AlbertHall

Joined Jun 4, 2014
9,272
Yes, the filter is the problem. The only way I can see of avoiding one would be to use a micro (or whatever) to measure and process the pulse period.
Yes, I thought of that. It does still get difficult when the period is multiple seconds, 1S, 10S...
 

Alec_t

Joined Sep 17, 2013
10,902
Shaft speed sensors on a car are faced with the same low frequency problem and overcome this by use of a multi-toothed reluctor wheel. This results in multiple sensor pulses per shaft revolution. Could you do something similar with your setup?
 

ian field

Joined Oct 27, 2012
6,539
Hello guys, I am new to AAC. I am working on a small sensor based project.
I am using a hall effect sensor (461C), which only respond to one polarity, thus producing a square wave. My supply is only a single rail 5V supply, so my square wave has amplitude of 5V. A magnet is attached horizontally to a motor and brought close to the sensor, which produces square waves of varying width according to the supply to the motor(which is between 0-3V)
Since it is a analog project, I have to convert frequency to analog dc voltage. On trying out different circuits such as peak detected, voltage doubler circuits, I was advised to use 4046 for FCV, since frequency that I get form my sensor is very small only between 0-100Hz.
Can I ask you to advice me one how to use 4046 as FCV and if possible a circuit diagram can help me.

Thank you in advance for all suggestions and help offered.
That would only use a small part of the 4046, and its not really designed for that application.

there were various voltage/frequency chips used in mode detection in early VGA multisync monitors - most application notes show examples of either way conversion.

The NE567 might be a candidate, but its a version of a PLL that I don't know much about. AFAICR: its listed as a tone decoder - a handy key word to search with.
 

Alec_t

Joined Sep 17, 2013
10,902
For my own interest I've come up with an analogue method of generating a voltage proportional to the pulse period. It updates within one pulse period and does not need a low-pass filter. However, since this is a homework thread, I think we need to let the TS come back with his own ideas before offering any further hints/guidance.
 

DickCappels

Joined Aug 21, 2008
6,185
Alect_t's post immediately above reminded me that this thread is in Homework Help. I checked and the thread starter has not been on the site since I made the post immediately above his, which included a detailed schematic. That post has been deleted. Thank you @Alec_t . I hope you can show us your other circuit sometime.
 
Top