help on LM2917

[kokhc]

i would like to convert frequency to voltage. i am using lm2917 14 pins to do it but i have some problem. i am not sure how to connect mt input since is it ranging from 1 to 3 V.

 

[Hero999]

Please don't ask the same question more than once.

Have you looked at the datasheet?

What part are you having trouble with?
https://www.electro-tech-online.com/custompdfs/2008/03/LM2907PDF.pdf

 

[audioguru]

His questions are all over the web. I already answered him or one of his classmates on another forum.

 

[kokhc]

sorry. i am totally new to such forum and i have problem uploading the thread, that is y i have it all over the web. won't do it again.

by the way, i am using the circuit in the datasheet page 8 (1st diagram).
the circuit is all right when i test it with a square wave signal generator. i believe it is my input problem. the input range is from 1 to 3 v, which mean that it is floating above Zero. i try to connect my input to pin 11 (+)and 1(-)
but i got weird reading. it is at 14v.

by the way, i am using this lm2917 for a flow sensor. the flow sensor output is in term of freqency, therefore i am using it to convert to voltage so i can read the output using an oscilloscope.

 

[kokhc]

add on:
the 14 v is not the correct reading because my frequency is only about 100Hz, which would onli give 1++V. even when my flow is switch off, it is still showing 14 v.

 

[audioguru]

The circuit on page 8 in the datasheet uses the 8-pins version which is different to your 14 pins version. Look on page 10 for your IC.

You need to bias pin 11 to half of your signal which is 2.0V with 2 resistors. When the input pin 1 voltage is higher than 2V then the circuit sees a high input. When the input is less than 2V then the circuit sees a low input.
The other wire of your signal source connects to 0V.