LED signage has become the choice in modern days to convey message to visitors of a venue. Be it corporate office, shops, restaurants or any kind of social functions like marriages. Some big and complicated display needs dedicated control PCs and designers to build contents for them. But for simple requirements a very low cost AVR microcontroller based PCB is enough. This kind of display shows a message that scrolls from left to right on a LED display screen. To make it easy to use they don't need any PC to program message to it. A PS2 keyboard can be attached and message can be typed. Message is stored in the internal EEPROM of the AVR and thus does not get erased even after the system is switched off.
In this article we will discuss design of such a control board that can drive four P10 displays which has a combined resolution of 128x16 pixels and 4 feet length. Height is 6 inches. This is perfect for most outdoor display requirements. We have chosen AVR ATmegs8 which is a 28 PIN microcontroller IC. This IC is low cost and is available at under 90 rupees (US$1.50) Thus the control board is very low cost and small in size.
Video of Working
Circuit Design
Circuit design for moving message display is very simple. At the heart we have put the ATmega8 microcontroller, which is connected to a 2x8 female header that can be plugged directly to the 2x8 male headers for P10 display. Since P10 displays are cascadable, and has a output terminal too, this terminal can be used to connect next display. In the same way one more panel can be connected. So a total of four P10 panels are cascaded.
One more thing that is connected to the ATmega8 is a PS2 connector where we can hookup a standard keyboard. PS2 connector only has 4 connections.
We do NOT use any voltage regulator ICs in this circuit because to power p10 displays we need a 5v 6A SMPS power supply which already regulates voltage to 5v. So we can connect this 5v directly to the ATmega8 also.
P10 LED Panel 32x16 Matrix
As you can see in the image above the module has a 16 pin header that is used to connect it to the controller board. The board also has a power input terminal that should be given a 5v DC input that can source upto 3A current. The output header is used to connect more P10 panels to make a larger display.
PIN Description of P10 LED Display
This LED display module has a 16 pin FRC box header for interface. Pin configuration is shown below.
As you can see most of the pins are ground. And that should really make you happy that this display is so simple!
- EN (Enable) is used for PWM brightness control of the entire panel. That means the MCU can control the brightness by feeding a pulse width modulated signal on this pin.
- A & B are the multiplex select pins. They take binary input to select any one of the four multiplex rows.
- Shift clock, Store clock and Data are the normal shift register control pins. The shift register IC used is IC74HC595
Connection with ATmega8
| P10 Display | Dev Board |
|---|---|
| GND | GND |
| EN | PB0 |
| A | PD3 |
| B | PD4 |
| Shift Clock | PD5 |
| Store Clock | PD6 |
| Data | PD7 |
Power Supply
The power supply shown below can easily supply current strong enough to run 3 to 4 P10 displays. All displays power input should be connected in parallel and finally connected to the power supply shown below. To buy the power supply click the image below.
PS2 Keyboard Connector
The image below will help you correctly connect the PS/2 socket. In this socket then you can easily connect PS/2 keyboard for typing. To buy PS2 connector please click here.
Cascading of P10 Displays
Connecting out port of one p10 display with in port of next display is called cascading. The image below will make it more clear. If you buy P10 displays from eXtreme Electronics, they ship the 16 pin cables with them so you not have to buy it separately.
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