Trigger led with both Arduino and tactile button

Question

I want to trigger a LED with both an Arduino and a hardware switch without coding any button logic in the Arduino.

^{simulate this circuit – Schematic created using CircuitLab}

When the button is pressed there is a direct connection between the 5V power supply and Arduino pin 17. Can this do any harm? Is there a better solution?

Answer 1

What you have drawn is a bad idea. If the Arduino output is low when the button is pressed, the 5V bus will be shorted. That's really bad. Instead, do something like this.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

Yes. There is a much better solution.

First off you need a resistor in series with your LED. Connect the resistor from the +5V and then to anode of the LED.

The switch would connect from the cathode of the LED to GND. When pressed the LED will go on.

The Arduino output needs to be operated in a mode where it changes from Input to Output@0 for its switching activity. Connect the output to the cathode of the LED. Under no circumstances should your software ever set the output pin to a '1' high level. You want to avoid the situation where a high output level can get shorted to GND by pressing the switch. To turn the LED on the pin is set low '0' as an output. To turn off the LED the pin is set to input mode.