“LED is a Display device with excellent performance, which has the advantages of long life, power saving, high brightness, multiple luminous colors, fast response speed and low driving voltage. According to the light mixing principle of R, G, and B three primary colors, a variety of colors can be called out, and then a variety of display effects can be realized through MCU intelligent control. Now it is widely used in urban lighting, architectural landscape lighting, stage lighting design and other fields.
LED is a display device with excellent performance, which has the advantages of long life, power saving, high brightness, multiple luminous colors, fast response speed and low driving voltage. According to the light mixing principle of R, G, and B three primary colors, a variety of colors can be called out, and then a variety of display effects can be realized through MCU intelligent control. Now it is widely used in urban lighting, architectural landscape lighting, stage lighting design and other fields.
Main chips: PCA9633/34/35: NXP I2 bus RGB/RGBA LED flashing/mixing chip; TEA152x: NXP power chip; LPC92x: NXP 900 series MCU; P82B96/PCA9600: NXP I2C bus driver chip.
1. Point light source: The principle of LED color screen display is applied, and its pixels are enlarged to reduce the overall cost. Each module is a color pixel. Application environment: bar, KTV, stage, shopping mall, exhibition hall, as music melody display, background wall decoration, curtain wall advertisement, etc.
2. LED rainbow tube: Each light tube is composed of multiple color pixels (RGB), and each single-color pixel can produce 256 gray-level changes. Application environment: decorative lighting in different places such as overpasses, river guardrails, building exterior walls, etc.
System hardware design:
The LED lantern control system mainly includes three parts: drive module, control module and LED power supply.
1. Drive module design
How to make the LED module show different colors mainly relies on the intermittent inertia principle of human vision, and uses the duty cycle of the three primary colors of R, G, and B to achieve color mixing. The LED color display of this design mainly relies on NXP’s I2C interface LED flashing/mixing driver chip PCA9633 (PCA9633-4-bit PWM output, PCA9634-8-bit PWM output, PCA9635-16-bit PWM output) to output 256 grayscale color to achieve color display. The controller only needs to transmit the grayscale value of the RGB color of the module to realize color display.
1. 4-channel LED driver, each driver can be programmed into four states through software, namely: on, off, programmable PWM flicker control output, programmable gray level for each channel, and supports four channels of PWM for overall brightness adjustment Mixed light output.
2. Dimming control, PWM output frequency is 97kHz, and each channel has 256 gray levels.
3. Flicker control, PWM programmable frequency range 24Hz~10.73s, duty cycle programmable range 0%~99.6%.
4. The overall brightness of the four-channel PWM output can be adjusted in 256 levels through the 190Hz PWM output.
5. The four-bit output can be programmed to be a push-pull output (at 5V, the sink current is 25mA, and the source current is 10mA).
6. 7 hardware address setting pins, the same I2C bus can connect 126 pieces.
7. Each PCA9633 has four programmable software addresses: one full response address and three sub-addresses.
8. Built-in 25MHz crystal oscillator and power-on reset circuit, and software reset can also be realized through the I2C bus.
9. SDA/SCL has built-in noise filter and supports 1MHz I2C fast mode.
10. Support hot insertion, low standby current, support voltage range: 2.3~5.5V.
The following figure shows the design of the drive unit, in which the number of red, green, and blue LEDs can be multiple. You can choose parallel or series according to your own design requirements, and then choose the appropriate LED according to the LED connection method and voltage/current requirements. A small number of LEDs can also be directly driven by PCA9633. For specific parameters, see PCA9633 data. The driver module sets the access address through the A6~A0 pins of PCA9633, and can work normally when connected to the I2C bus output by the control module. Each I2C bus can be connected to 126 dimming driver modules.
2. Control module design
The control module is shown in the figure below. The main function is to control all dimming modules on the I2C bus through the MCU to achieve various display effects. P82B96 is an I2C bus driver chip, which is used to improve the bus driving capability. The transmission rate is 20~50kbps When the transmission distance can reach 1km. The MCU can be selected according to the actual system requirements, and other operations can be added while controlling the dimming of the bus device, such as displaying image processing, communicating with PC, expanding storage space and so on.
Design of LED Display Control System Based on I2C Interface Driver Chip PCA9633
3. Power section
The specific parameters of the power supply should be determined according to factors such as the specific number of LEDs and connection methods. The following figure shows the LED power supply scheme using NXP STARplug series chips. This scheme has the advantages of simple design, small size, wide voltage input, low cost, low loss, etc. It is widely used in the field of LED.
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Link to this article：Design of LED Display Control System Based on I2C Interface Driver Chip PCA9633