Summary of How to drive an led display matrix using PIC16F88
This article explains how to drive an 8x8 LED matrix (64 LEDs) or smaller arrays using only 10 microcontroller pins. It achieves this via multiplexing and persistence of vision, where rapid sequential lighting prevents visible flicker. The project utilizes a pre-wired module but notes that DIY wiring follows the same logic.Parts used in the LED Matrix Project:
- Red 8x8 LEDs
- Multiplexing driver chip
- Microcontroller with 10 output pins
- Dot matrix LED display module
It uses persistence of vision to let you drive the 64 led matrix with only 10 microcontroller outputs!
Normally you would need 64 outputs for 64 LEDs but by using multiplexing and a helper chip you can get away with 10.
LED Display multiplexing simply means turning on one led for a short period of time and doing this repeatedly for each LED.
If you do this fast enough then your eye will not notice any flicker.
Note: The unit used in this project is simply an array of 64 LEDs.
The LEDs are no different to any other LEDs but it saves a huge amount of soldering as all the wiring has been done for you.
...Or you could wire it up yourself if you can't get hold of the module.
If you wire it yourself you still only need 10 control wires (just wire you leds the same as shown in the module diagram).
A dot matrix led display is simply a grid of LEDs arranged for use by multiplexing.
Specification
| dot matrix led display driver | Red 8x8 LEDs |
Multiplexing
If you tried to drive 64 individual LEDs you would need 64 individual output pins (each led connected to a output pin on one side and ground on the other).
Obviously that is a tall order so the way round it is to use persistence of vision which is a way of describing how your eye works.
Your eye reacts slowly to changes in light intensity so that if a light is turned on and off quickly enough then it does not notice that the light is off. Basically your eye remembers a light pulse for a short time.
The approximate time is 20ms so if the light is turned on at a frequency >50Hz (1/20ms) then your eye will not notice any flicker at all.
Multiplexing uses this fact to reduce the number of pins needed to drive an LED display. You can do this by splitting the 64 led display into 8 rows and 8 columns which lets you drive it using 8 row outputs and 8 column outputs. In fact the 8x8 led matrix block used here has all the leds arranged in this way already.
For more detail: How to drive an led display matrix using PIC16F88
- How many pins are needed to drive a 64-LED matrix?
You only need 10 microcontroller outputs instead of 64. - What principle allows reducing the pin count?
Persistence of vision and multiplexing allow driving the display with fewer pins. - Can you build the matrix yourself without a module?
Yes, you can wire it yourself if you cannot get hold of the module. - How is the 8x8 display arranged for multiplexing?
The display is split into 8 rows and 8 columns. - At what frequency does the eye stop noticing flicker?
The eye will not notice flicker at a frequency greater than 50Hz. - Does the DIY wiring require different control wires than the module?
No, DIY wiring still requires only 10 control wires. - What is the approximate time your eye remembers a light pulse?
The approximate time is 20ms.
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Ibrar Ayyub
I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough...