I am doing some simple LED circuits and had a quick question on running a large number of simultaneous LED’s (100+) with the arduino.
My goal is to have the LED’s powered by a separate 9V source and have the on/off functionality via a 120 transistor with the arduino digital pin going to the base. Basically, I am trying to adapt this circuit (borrowed from elsewhere on this forum) to use an external 9V to power the LED’s as opposed to the arduino-provided 5V. I had this thread on the forum (http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1200895650) about the limits of the current able to be provided by Arduino and the reason I am trying this modification.
Thank you for your time as I muddle my way through this. My end project after my learning curve is a version of the LED Fan Sign I saw on the MAKE podcast to help promote the Minnesota Twins.