Monitoring LED state using digital input

Other Hardware General Electronics
1

Hello everyone!
I am planning to monitoring the state of 16 LEDs connected to a simple board. But the LEDs are switched on using 1,8 volts, so how can I use digital input to check their status? Because digital input on Arduino side only work with voltage > 3 Volts to detect high and low status. Thank you.

2

Do the LEDs have current limiting resistors?
Voltage on the other side of CL the resistor might be higher.

If the LEDs are connected to ground, you can use a small NPN transistor.
Emitter to ground, base via 1k resistor to LED anode, collector to a digital pin with internal pull up.
Leo..
LED.png

LED.png

3

Wawa:
Do the LEDs have current limiting resistors?
Voltage on the other side of CL the resistor might be higher.

If the LEDs are connected to ground, you can use a small NPN transistor.
Emitter to ground, base via 1k resistor to LED anode, collector to a digital pin with internal pull up.
Leo..

Thanks WAWA. Is there any option to connect multiple arrays? I was planning to use the ULN2803 but its input senses voltage over 2,4 volts. Thanks again.

4

The ULN2803 should have a threshold of ~1.3volt, and might work ok with 1.8volt from the LED and the small pull down current of the internal pull up resistors of the Arduino pins.
Leo..

5

Wawa:
The ULN2803 should have a threshold of ~1.3volt, and might work ok with 1.8volt from the LED and the small pull down current of the internal pull up resistors of the Arduino pins.
Leo..

Thanks a lot, I´ll give it a try! Best regards.

6

ULN2803 as octal comparator - clever!