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Thursday, 4 September 2014

Circuit to Connect Current Limiting Resistors to LED Matrix (Page 1)

by realfinetime  |  in Electronics at  11:34

User Friendly Method to Display Texts on 8*8 LED Matrix

          LED matrix is an interesting electronics component that most of the electronics beginners want to work with. A common doubt that arise in most of the beginners is about the over current protection system for LED matrices. Current limiting resistors are important for LED matrix. A circuit diagram in which current limiting resistors connected to cathode pins of LED matrix is given below.

          If current limiting resistors are connected to the anode or cathode pins of LED matrix, when all LEDs of a particular column turn on, brightness of LEDs will decrease considerably because, current will split to eight parallel paths. But, if only one LED is on, entire current will flow through that single LED. This will increase the brightness of this LED considerably. This is because of the large current that flows through these LEDs. If current limiting resistors are not connected, when only one LED is on, large current will flow through this LED because of the small resistance of LED which may permanently damage that particular LED. If any of the LED in an LED matrix is damaged, entire matrix will become useless. When a 5V power supply is given, 100 Ohm current limiting resistor is enough.

          As we all know, LED matrix works based on the principle of persistence of vision. This can be easily illustrated using an example. If you want to display 'H' in an 8*8 LED Matrix, you can use two methods.

Method 1:

Program will generate eight frames as shown below.
            When these eight frames are displayed at a high speed one after another, eye will get a feeling of 'H' because of the phenomenon of 'persistence of vision'.

          If your display works based on method 1, current limiting resistors of 100 Ohm should be connected to the cathode pins (4, 7, 2, 8, 12, 1, 14, 9) of LED matrix if the supply voltage is 5V.

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1 comment:

  1. This is really interesting. I want to try this. Hmmmm I think I need fluke 117 electricians true rms multimeter here beside me while doing this project LOL



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