LM358 Comparator Output High Even When Non-Inverting Input Is 0V—Why?

Hi
I was using LM358 as voltage comparator in non inverting configuration
I gave 5V to vcc and 2.5V to inverting pin through a potentiometer
The issue is I am getting a output voltage of approx 3.8V even when the supply to the non inverting terminal is zero

I get output no matter I set the voltage of the non inverting pin zero or less than or more than that of inverting terminal
Also the ic gives the same output when non inverting is given some voltage and inverting is zero

The ic output gets zero only when both inverting and non inverting terminals are zero

Please help me to sort this

I desire to get high output only when the voltage at non inverting is greater than that at inverting i.e 2.5V

You have to be careful using an op-amp, even an older low bandwidth type like the LM358, as a comparator. It
is often done, but you have to be careful using an op-amp open loop. It does not have rail to rail output, so you won't get 5V out. It also helps to put in some hysteresis, and you need to keep noise away from the inputs (no long leads) and make sure the power supply is decoupled at the power supply pins. There is a possibility that it is oscillating.
See this brief article https://www.analog.com/media/en/technical-documentation/application-notes/AN-849.pdf
Cheers,
Richard

Hi
I give you an alternative solution using the MCU 16F876 and its ADC ports. When the voltage on a port is greater than the voltage of the other port, then the LED will be ON. Otherwise OFF.
Cheers
Giovanni

=============================

Listing

#chip 16F876,20
#config OSC=HS

Dir PORTB.0 Out
Dir PORTA.0 In
Dir PORTA.1 In

start:

v1=ReadAD(AN0)
v2=ReadAD(AN1)

if v1>v2 then portb.0=1 else portb.0=0

wait 100 ms

goto start