Pixel LED is a LED that can Illuminate any color within the RGB color schemes at a given time.The basic RGB LED have a common pin and three other pins for red ,green and blue color anodes or cathodes. If you want to generate a color you need to apply voltages to each RGB pin depending on the RGB color ratio.If the LED is a common Anode the common pin needs to be connected to the (+) positive terminal of the power supply.If its a common cathode the common pin needs to be connected to the (-) or the ground of the power supply .eg- If you need the white color to be Illuminate , You have to apply same voltage level to each R,G and B pins, like wise if you need yellow color , give same voltage to the R and G pins and no voltage at B pin.The voltage level decides the brightness of the Illuminated color.But this method of driving pixel LEDs complicated when it comes to controlling multiple RGB LEDs. That's where the pixel led drive IC's comes to play. using these ICs You can drive given amount of pixel LEDs with only three or four wires.Another benefit of using these ICs is that you can decide the each color with numeric values ( 0- 255) . You can connect these pixel LEDs to the Pixel LED controllers and create animations or videos with the help of software like [ LEDEdit ].
Reasons for making your own Pixel LED
⬤ Limited Options - If you are looking for ready-made Pixel LEDs or LED strips online , you may find it difficult to find a one with the type or shape of the RGB LED you needed.
⬤ Different Design - You may have a different design other than pixel LED strips or strings.
⬤ Cost Effective - When you are doing larger projects , buying a large quantity of pixel LEDs and pixel LED controller ICs and assembling them is cheaper than buying ready-made pixel LEDs .
⬤ Customization - If you are building your own pixel LEDs, you have large verity of options to be choose from such as the LED type, PCB and drive IC type . These options are not available for ready-made pixel LEDs.
Selecting the LED bulb for pixel LED
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| Different types of RGB LEDs |
When you selecting a RGB LED's (tri-color LED) for your pixel LEDs there are few things that you should take into consideration.
⬤ Type of LED - Through hole and SMD - The type you selects should based on your needs such as PCB design and space requirements . Common pin type - There are three types common anode , common cathode and the separated pin (no common pin) .Separated pin type can be used as both common anode and common cathode by connecting the common pins together in the PCB .Common pin type depends on what pin type drive IC supports.
⬤ Shape - There are several options when it comes to the shape of the LED.Most common type is dome type RGB LED , But there are other designs too such as round shape ,square shape and rectangle shape etc.
⬤ Size - Through hole type RGB LEDs comes with few standard sizes such as 3mm , 5mm , 8mm and 10mm . But , When it comes to SMD RGB LEDs there are large variety of sizes . The size of the LED effects the overall design of the pixel led unit so selecting a LED that mach your design specifications is very impotent. To refer the size specifications ask for the datasheet for the RGB LED from the vendor (size specifications usually at the end of the datasheet).
⬤ Electrical specs - Electrical characteristics such as wattage , voltage and the junction temperature need to be taken to consideration when designing a pixel LED ,Depending on the design specifications choose a RGB LED that suit your needs . To refer to electrical specifications ask for the datasheet for the RGB LED from the vendor .
The Pixel LED Drive IC
Pixel LED Driver IC is a special type of a IC that designed to make the use of pixel LED easy by making communication between pixel LEDs and pixel LED controller with a limited amount of wires. This allows the pixel LED controller to address each and every pixel led in the network of pixel LEDs with only using one or two outputs of the pixel LED controller.
Selecting the Pixel LED Drive IC
There are few considerations that you have to take when it comes to selecting a pixel LED driver ICs . Because there are large collection of controller IC's selecting a controller IC can be little bit hard. Here are a list of things to consider when it comes to pixel LED drive ICs.
⬤ RGB LED Type - The type of the RGB LED that you selected have lot to do with the type of the pixel LED drive IC because the electrical characteristics of the LED affects the drive chip. RGB LED's current and voltage needed to be taken to consideration these characteristics should be below the maximum values of the IC .
⬤ IC Dimensions - The package size of the drive IC need to be taken to consideration when you are designing a pixel LED. The pixel LED driver ICs usually comes in two packages Through hole type package and surface mount(SMD) type package. If you wants to save the space , the best option is to go with the SMD package.
⬤ Electrical Characteristics - The electrical characteristics such as supply voltage, Output voltage , Input voltage , Output current and Input current need to be taken to the consideration when designing pixel LEDs .
• Supply voltage - This is the voltage range that IC operates usually 4.5Vdc - 6.5Vdc.
• Output voltage - This is the voltage range of ICs output pin .
• Output current - This is the maximum current through ICs output pin . This effects the LED type that can be used with the IC.
• Input current - This is the current that IC takes. This value is important when it comes to deciding the overall current of the system .
⬤ Communication protocol - This is the method how the pixel led controller or the micro controller communicate with the pixel led drive IC .There are several communication protocols used by these ICs such as NRZ (Non Return to Zero) , I²C and DMX512 . The NRZ method only uses single wire to transfer data , but limits the communication speed .The I²C method uses two lines (wires) for the communication data and data clock .
⬤ Switching characteristics - These are the drive ICs characteristics of data transmission signals such as Operation frequency ,Transmission delay time ,Fall time ,Data transmission rate ,Input capacity. These things affects the frame rate and data transmission limitations .
Designing the PCB for pixel LED
Before designing a PCB diagram needed to be studied. Since each drive ICs have different pin outs and different configuration .Diagrams differ from IC to IC. Here is a list of popular pixel LED drive ICs. Select a drive chip IC from bellow links to learn how to design PCB's using each of them.
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