Need some help creating a circuit to detect when a USB device is charging and illuminating a status LED.

Thread Starter

RussellReal

Joined Aug 18, 2022
16
the - reference voltage wire is attached, I just realized if the positive reference voltage is attached directly to ground that the voltage is lower than the negative reference voltage so the led goes off... so I guess if there is no positive reference the negative reference is the ONLY reference, so it doesn't compare it just passes power through, thats contrary to how I expected it to work.

1661107782364.png
 

crutschow

Joined Mar 14, 2008
38,690
Yes, the small positive reference voltage at the op amp minus input should keep the LED off if there is no current flowing in the load.

Please post a circuit diagram of what you have, not a breadboard picture, which I am not inclined to wade through.
 

LowQCab

Joined Nov 6, 2012
5,101
Here are some simple videos that explain how
an Op-Amp works when used in a "Comparitor" configuration,
( which is how this Circuit is meant to operate ).


Here's another video that also explains the use of an Op-Amp as a Comparitor,
plus gives further information about other Op-Amp functions.

.
.
.
 

BobTPH

Joined Jun 5, 2013
11,618
You have no connection to the + input on the op amp you are using. All inputs of an opamp must be connected in order for it to work properly. That includes the ones on unused opamps. Complete the circuit before assuming it does not work.
 
Top