Institute of Electrical and Electronics Engineers

WE ENGINEER EXCELLENCE

LED Bars

Tutorial: LED Bars and Bussed Resistors

In CS120B you will often be switching entire ports of you microcontroller at once. To save tedious discrete component wiring, IEEE has provided LED bars and bussed resistors. This lowers the component count from sixteen to two. 

Both components have a polarity: that is, the LED bars have a small notch in the corner denoting the anodes, and the bussed resistors have a small dot on one side that shows the bussed end. 

 

schematic led bar
Schematic
LED bar tut

 

 

 

 

 

 

 

 

An LED bar connected to PORTB with the notch facing the port. The bussed side with the dot is grounded. Also notice that the bussed side of the resistor is in a breadboard row with no LED. All ten LEDs are usable. 

 

The LED anodes are on the side with the notch. Each LED has its own resistor.  

 

Schematic2
Schematic. Again notice how two of the LEDs are not usable, especially the one connected with no resistance.
led bar 2

 

 

 

 

 

 

 

 

Alternate configuration with LED bar connected to Port A. There are no isolated resistors anymore, but the two left LEDs are not usable. (one is connected to GND with no resistor and the other is not connected to anything)

 

The length of your 1k resistor array will vary from eight resistors (nine pins) to ten resistors (eleven pins). If your array is eight resistors long, use discrete resistors for the last two pins.