Output from voltage comparator drops to 0.6 V when connected to micro controller? - Electronic Circuits Projects Diagrams Free

Drohm · 4th May 2008, 05:31 PM

Hi all,

I have made a voltage comparator out of a 5 V powered LM358N opamp and it is working just fine. But when I connect the output to digital in on a micro controller (PIC 18F4550) the voltage drops to around 0.6 V and the the low voltage is not enough to trigger the input. I have tried to remedy the problem by using the other half of the opamp as a voltage follower but with no luck.

Do you have any idea to what the problem might be?

Regards
Drohm

ericgibbs · 4th May 2008, 05:43 PM

Quote:

Originally Posted by Drohm

Hi all,

I have made a voltage comparator out of a 5 V powered LM358N opamp and it is working just fine. But when I connect the output to digital in on a micro controller (PIC 18F4550) the voltage drops to around 0.6 V and the the low voltage is not enough to trigger the input. I have tried to remedy the problem by using the other half of the opamp as a voltage follower but with no luck.

Do you have any idea to what the problem might be?

Regards
Drohm

hi,
Are you sure the PIC pin is not configured as an output.?

Do you have a drawing.?

BTW, you have posted this question 3 times..

Drohm · 4th May 2008, 05:48 PM

Hi,

Yes Im sure the PIC pin is not configured as output. It works just fine if I put 5 V directly on the pin.

Yeah I know it is posted 3 times Im trying to delete two of the posts

I dont have a drawing at the moment, but I will make one very soon.

**Nigel Goodwin** · 4th May 2008, 05:57 PM

Quote:

Originally Posted by Drohm

Yes Im sure the PIC pin is not configured as output. It works just fine if I put 5 V directly on the pin.

If you've connected 5V directly to the pin, and it's configured as an output, then you may well have damaged the pin - you should connect any input via a current limiting resistor.

I agree with ericgibbs, you've most likely got the pin configured as an output, and set low.

Drohm · 4th May 2008, 06:24 PM

Yeah, you might be right. But how does that explain that it works with 5 Volts then?

**Nigel Goodwin** · 4th May 2008, 06:26 PM

Quote:

Originally Posted by Drohm

Yeah, you might be right. But how does that explain that it works with 5 Volts then?

If you're connecting 5V directly to the pin it's destroying the output stage feeding the pin - it's not something you should be doing!.

Drohm · 4th May 2008, 06:29 PM

Ok, thanks for the help!

I shall return as soon I have checked the code...

ericgibbs · 4th May 2008, 06:41 PM

Quote:

Originally Posted by Drohm

Ok, thanks for the help!

I shall return as soon I have checked the code...

hi,
If you want to double check, post your code.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar
Title	Starter	Forum	Replies	Latest
micro controller projects	melodzky	Micro Controllers	3	4th July 2005 08:41 AM
output voltage drop of 555 timer ic	mozikluv	Electronic Projects Design/Ideas/Reviews	4	18th November 2003 03:49 AM
changing dc power supply output voltage???	seaball	Electronic Projects Design/Ideas/Reviews	3	6th August 2003 11:11 PM
voltage output	bogdanfirst	General Electronics Chat	3	18th July 2003 07:50 PM
Micro Controller Switcher Help	Fuad	General Electronics Chat	3	25th May 2003 08:48 AM

4th May 2008, 05:31 PM	#1
Drohm	Output from voltage comparator drops to 0.6 V when connected to micro controller? Hi all, I have made a voltage comparator out of a 5 V powered LM358N opamp and it is working just fine. But when I connect the output to digital in on a micro controller (PIC 18F4550) the voltage drops to around 0.6 V and the the low voltage is not enough to trigger the input. I have tried to remedy the problem by using the other half of the opamp as a voltage follower but with no luck. Do you have any idea to what the problem might be? Regards Drohm

4th May 2008, 05:48 PM	#3
Drohm	Hi, Yes Im sure the PIC pin is not configured as output. It works just fine if I put 5 V directly on the pin. Yeah I know it is posted 3 times Im trying to delete two of the posts I dont have a drawing at the moment, but I will make one very soon.

4th May 2008, 06:24 PM	#5
Drohm	Yeah, you might be right. But how does that explain that it works with 5 Volts then?

4th May 2008, 06:29 PM	#7
Drohm	Ok, thanks for the help! I shall return as soon I have checked the code...