I am looking for a ciruit which allows switching an LED according to a digital (bus) signal. The actual signal should only be minimal affected (rise time etc.).
An example: Light up an LED when a SPI device is selected by ~CS. I dont want to use another digital pin of the master for this. What circuit would be appropriate?
My thought was using a Darlington transistor as it is available in arrays in an IC (e.g. ULN2003D) and should work with low currents to switch Q1:
Is this a good approach and how large should R2 be? Note : The SPI ~CS Example needs an additional NOT gate to flash the LED when the Slave is selected.