16 LED Controller

Abstract

Design a 16 channel red, green, and blue (RGB) light emitting diode (LED) controller capable of sourcing up to 100mA per channel by the most cost effective means possible. The design contains a microcontroller for uploading programs an allowing the PCB to functionindependently from an external source. Each color of all 16 LEDs should be individuallycontrollable via an SPI connection traversing across each IC. The overall goal is to use aCAT4016 16-channel constant current LED driver for the design to demonstrate its functionality and possibility for use in other LED related projects. The primary design component consists of designing the PCB, using Cadence Allegro, to comply with all the manufacture parameters.

Board Top

Board bottom

Project Description

The design uses a 16-channel constant current LED controller (CAT4016) for each LED color allowing for individual color control. The LED driver integrated circuit communicates with a 44-pin ATMEL ATMEGA644A microcontroller by serial communication. The CAT4016 LED controllers are daisy chained together minimizing the number of IO port necessary to set thecolors. The program sends each color out in a set of 16 data bits, totaling 48 bits of data transfer for each set-up cycle. The data is latched in the shift registers of the ICs and then output based onthe enable pin on the IC. Each enable pin is controlled by the microcontroller allowing a single color output if desired. If all 16 RGB LEDs are turn on at once, producing the color white, thesystem draws a total of 1 Ampere. The input voltage can range from 3.3V to 5V depending onthe power supply. The design includes several capacitors to reduce input noise and improve thereliability of all the ICs and LEDs. The LED current is set to 20mA using an external resistors onthe RSET pin of the CAT4016. The blue and green portions of the LEDs have a turn on voltage3.2-3.3V and red of 2.2V.The overall goal of the project is to demonstrate the functionality of the CAT4016 constant current drivers for RGB LED control. The design incorporates analog inputs, allowing the board to be used as an analog voltage level indicator by changing the program on the microcontroller.

Assembled components

Design Parameters:

• Maximum board size 4x6

• Minimum 10mil trace width

• Minimum 10mil spacing

• Minimum 15mil vias

• Minimum 20mil traces for LED connections to reduce resistance (voltage drop)

• Polarity Capacitors to clean incoming DC noise

• Provide ISP programming connection for ATMEGA644A microcontroller

• LED for power indicator

• LED for programming indicator

• Button for mode switching

• Extra set of LED connections for all 16

Conclusion

Designing the schematic and PCB using Cadence Allegro proved to be rather challenging especially without any prior knowledge of how the program operated prior to this experience.Allegro provides a versatile platform allowing the user to full customize the design based on the desired specifications. Designing the schematic image and footprint and associated the pins between the two took several trial and error runs. Once the entire library was developed, alongwith the footprint, placing the components in the schematic moved very smoothly with theprovided tutorials. Creating the 4-layer board moved relatively smoothly, aside from issuesgetting vias to fall within parameters. The real issues came when attempting to transfer everything over to a 2-layer board. The major problem was removing the extra layers and deleting the AutoRoute traces. The next major issue development from adjusting the via sizes to meet the 15 mil compliance. The final major issue involved using AutoRoute while still keepingthe desired power traces intact. Once all the issues were worked out the PCB passed the manufactures DRC and moved on to production.With the passage of one week the PCB return complete, and the major traces were tested toensure proper connectivity. All the components were soldered to the board and the solder jointswere inspected for good contact. Any connections that appeared to have issue were re-soldered.The completed board was plugged in to a 3.3V power source and tested at specific contact pointsand solder connections. The entire design appears to operate correctly and only requiresprogramming. Overall the PCB design is a great success.

Downloads

Related Content