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This article is intended to provide a quick reference guide for LED Matrix Panel design.
The system described here is for 16 x 32 RGB LED panel, however the same concept applies to the displays of bigger size.
These displays are nowadays widely used as digital signage systems for indoor and outdoor advertising.
The basic building blocks of a LED panel are :
16 x 32 LED Matrix Panel : How it works ?
A 16 x 32 LED panel consists of 16 Rows x 32 Columns of RGB LED’s.
Each LED is illuminated or controlled by selecting the specific Row and Column where it is connected.
The Rows of the Panel are connected to the 4 to 16 decoder IC, which can select the desired row by 4 input signals A0-A3.
The Columns of the Panel are connected to 32 bit shift Registers. These Registers are connected to the RGB pins of the LED’s.
The Inputs to the Column drivers are the RGB signals, Latch enable signal, Blanking signal and a Clock signal.
These Control and data Inputs can be connected to the external controllers by a HUB75 Connector.
The function of the shift Register is to convert the serial Input to the parallel outputs.
The Columns of the panel have a serial data input, blanking Input, shift register and a parallel output register. The data present on the serial data input is shifted into the shift register by the clock input SCLK signal. Once the entire data is shifted into the 32 bit Registers, the latch signal is used to transfer the row of the pixel data to the output register.
The blanking signal is used to transfer the data from the Output register to the LED’s.
The decoder IC such as 4:16 decoder can be used to Multiplex Rows selection.
This Multiplexing is used to select only few rows to be active or ON simultaneously thereby avoiding the need of switching ON all the LED’s at the same time and increasing current consumption.
The term used to describe this functionality is called as the scanning rate and the variants can be 1/16,1/8,1/4 etc.
A 1/16 scan rate implies that only one row can be active at a given instance and it requires 4:16 decoder with 4 control inputs.
A 1/8 scan rate implies that only 2 rows can be active simultaneously at any given instance and it requires 3:8 decoder with 3 control inputs and so on.
The scanning of the Rows and Columns has to be at continuous rate so that the display appears as an image without flickering. each rate of the scanning is called a refresh cycle.
A Refresh cycle of a panel consists of the below steps :
- Shift the RGB data into the shift registers using the RGB and the Clock Inputs.
- Until the full row data is filled in, Blanking Input signal is used to blank the display.
- Once the Shift Registers are loaded, the latch signal is used to transfer the data to the output register.
- The Blanking signal is set low to display the data from the output registers to the LED’s.
- Repeat the above process for all the Rows in the Panel.
- Repeat the entire above process for 100-200 times within a second to prevent flicker.
LED panel Controllers
The function of the Controller is provide the data and control inputs to the panel through the HUB75 connector.
There are two types of Controllers : synchronous and asynchronous controllers.
A synchronous display controller simply presents the data from a computer to the panel. It provides the real time data of pictures and videos which is displayed on the connected computer.
An asynchronous display controller does not need to be connected to the computer, a usb or a wireless connection can be used to provide the content to the controller to display in the panel.