Broken LED detector

[max_torch]

Say I create a LED matrix powered by a microcontroller, what could I do to detect if an LED is broken? I want to make a feedback to the microcontroller that will alert it when an LED is not lighting even though the microcontroller is sending a signal to turn it on.

 

[(*steve*)]

you could sense the ground current to the array and then scan the array one LED at a time. If you don't sense current (or perhaps if you sense too great a current) then the LED is probably not working correctly.

 

[AnalogKid]

Say I create a LED matrix powered by a microcontroller, what could I do to detect if an LED is broken? I want to make a feedback to the microcontroller that will alert it when an LED is not lighting even though the microcontroller is sending a signal to turn it on.

A scanned LED array can have constant current source or sink drivers, or simple current limiting resistors. Either way, there is an impedance that creates a voltage drop, and that drop can be measured or compared to determine if there is an open circuit. If you want to identify which LED has failed, the detect-report-process actions must take less time than the ON time for each LED.

For example, assume an LED array with five columns and seven rows, with the LED anodes connected to the row outputs and the cathodes connected to the column switches through resistors to GND. A comparator with a 1 V trip point is connected to top of each resistor, and the five comparator outputs are wire-OR-ed into a uC input.

Turn on a row output
Turn on a column output
Test the Fail input
IF Fail = 1, do something
Move on to the next row/column combination

ak