The problem:
LM2917 Vout decrease with the same input frequency along time.
The LM2917 input is the Hall sensor (APS11450) output.
The sensor reads 8 magnet per revolution.
Fixed frequency about 30 Hz.
470 ohm in Vcc line to Vcc LM2917 (Zener regulated).
Vout from 0 - 5 V.
The Vout decrease about 0.05 V each time I have measured but the frequency is always the same.
I have doubts when the Vout tends to decrease, when the IC LM2917 is only feeding but not reading input frequency, or when 2917 is feeding and reading frequency too.
I registered the Vout day by day and is still decreasing. All the boards that I tested have the same trend. Also changing so many time the value of the timing parts (C3, R2 and C4) of the scheme. Always same results, the Vout decrease with time.
Did somebody see something like that?
I attached the electric scheme.
Also I enclose LM2917 pin 1 input oscilloscope capture.
