Summary of How to drive a Dot Matrix LED Display. using pic microcontroller
This article explains how to drive a 64-LED (8x8) dot matrix display using only 10 microcontroller pins by employing multiplexing and persistence of vision. By rapidly cycling through rows and columns, the human eye perceives a continuous image without flicker. The project utilizes a pre-wired LED module or custom wiring with an 8-bit PIC microcontroller (16F88/16F84), controlled via MikroC compiler software.
Parts used in the Dot Matrix LED Display Project:
- Red 8x8 LEDs dot matrix display
- Mikroelectronika MikroC Compiler
- PIC Microcontroller (16F88 or 16F84)
Driving a 64 LED dot matrix LED display is quite simple and just requiresONE TRICK!
Here you can find out how to drive an led dot matrix with 64 LEDs (8 rows by 8 columns – 8×8 display) or less e.g. 35 LEDs (7 rows by 5 columns – 5×7 dot matrix). However the principle remains the same for larger displays – you may need more processing power and driver circuitry though.
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
Specification
| dot matrix led display driver | Red 8×8 LEDs |
Dot matrix LED display project details.
| Compiler | Mikroelectronika MikroC Compiler Free! |
| Target | 16F88/16F84 (retargetable to other PICs that have an enough pins). |
| Software level | Easy. |
| Software notes | Multiplexing the display. |
| Hardware level | Easy. |
| Hardware notes | No special notes |
| Project version | 1.04 |
| Project files | Enter your details to get the Download Link and get the microcontroller newsletter: (Your email is safe it will never be sold or rented). Note: Check your email for the project code download link. |
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 8×8 led matrix block used here has all the leds arranged in this way already.
64 LEDs.
The 64 leds are housed in a plastic casing, wired up inside ready for multiplexing (8 row connections and 8 common column connections). The LEDs are no different to any other LEDs but the LED block 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 your leds the same as shown in the module diagram).
For more detail: How to drive a Dot Matrix LED Display.
- How many output pins are normally needed for 64 LEDs?
You would need 64 individual output pins if driving each LED separately. - Can you drive a 64 LED matrix with fewer than 64 outputs?
Yes, you can drive it with only 10 microcontroller outputs using multiplexing. - What principle allows the eye not to notice flicker?
Persistence of vision allows the eye to remember light pulses for about 20ms. - At what frequency must the light be turned on to avoid flicker?
The light should be turned on at a frequency greater than 50Hz. - How is the 64 led display split for multiplexing?
The display is split into 8 rows and 8 columns. - What microcontrollers are suitable for this project?
The project targets the 16F88 or 16F84, which can be retargeted to other PICs with enough pins. - Is special hardware required for the driver circuitry?
No, there are no special notes regarding hardware requirements. - Does the project support displays smaller than 64 LEDs?
Yes, the principle remains the same for displays like a 7x5 matrix with 35 LEDs.
