I have a bunch of red LEDs, I don't have their data sheet and I am trying to figure out a safe resistor to use to lower the current across them safely.
My current setup is as follows:
I figured a 100 Ohm resistor and 68 ohm resistor in series because, assuming a forward voltage of the led of 3 volts, and a desired current of 20mA (which I assume is ok?) I get:
R=V/I R=3.3/0.02 R=165 Ohms.
So, I pop that into the circuit lab as shown below, click run, then click DC simulation, but then it just throws an error saying :
"unable to get solution"
How do I use this tool to allow me to inspect various values at various points in the circuit? Have I got this wrong somehow?!