Order As Required
Our Code: SKU-004058
Supplier: [Pololu MPN:3091]
This high-density LED strip has a length of 0.5 m and contains 72 RGB LEDs that can be individually addressed using an easy-to-control SPI interface, allowing you full control over the colour of each RGB LED.
These flexible RGB LED strips based on the SK9822 LED/driver IC are an easy way to add complex lighting effects to a project. Each LED has an integrated driver that allows you to control the colour and brightness of each LED. The SK9822 has constant current control, so voltage drops caused by the resistance in long power connections have little effect on the SK9822’s colour and brightness as long as the voltage stays above 3.5 V.
In contrast to the SK6812 used in some of our other similar LED strips, which use a specialised one-wire control interface and require strict timing, the SK9822 uses a standard SPI interface for control (with separate data and clock signals) and has no specific timing requirements, making it much easier to control. Another useful feature of the SK9822 is an additional 5-bit brightness control register that allows you to dim your LED strip while still having 24-bit colour control. See below for a more detailed comparison of the SK9822 and SK6812.
These SK9822-based LED strips work as a drop-in replacement for our older APA102C-based strips in many applications. However, due to slight colour differences, we generally do not recommend using the SK9822 and APA102C together in the same project. Also, due to a slight difference in the protocol, you might have to update your code to handle the SK9822. See below for a more detailed comparison of the SK9822 and APA102C.
We offer six different kinds of SK9822 LED strip with different LED densities and lengths. Our strips with 30 LEDs per meter are available in three lengths:
We also offer denser SK9822 LED strips that have 60 LEDs per meter:
Our highest-density strip has its SK9822 LEDs packed together as tightly as possible, resulting in 144 LEDs per meter:
We also have SK9822 LEDs available in panels.
This strip is 0.5 meters long and has 72 LEDs with a density of 144 LEDs per meter.
Each LED strip has three connection points: the input connector, the auxiliary power wires, and the output connector. These can be seen in the adjacent picture, from left to right: auxiliary power wires, input connector, output connector. The strip uses 4-pin JST SM connectors.
The input connector has four male pins inside of a plastic connector shroud, each separated by about 0.1″. The black wire is ground, the green wire is the data signal input, the yellow wire is the clock signal input, and the red wire is the power line.
The auxiliary power wires are connected to the input side of the LED strip and consist of stripped black and red wires. The black wire is ground, and the red wire is the power line. This provides an alternate (and possibly more convenient) connection point for LED strip power.
The output connector is on the other end of the strip and is designed to mate with the input connector of another LED strip to allow LED strips to be chained. The black wire is ground, the green wire is the data output, the yellow wire is the clock output, and the red wire is the power line.
All three black ground wires are electrically connected, and all three red power wires are electrically connected.
These LED strips ship with flexible silicone brackets and screws. Strips with lengths of 1 m or greater include five brackets and ten screws per meter. Our 0.5 m high-density strip ships with a total of two brackets and four screws. The brackets fit over the waterproof sheath and can be used to mount the LED strip. The LED strip also ships on a plastic reel.
Note: The strips with 30 LEDs per meter are slightly narrower than the denser strips, and the brackets included with those strips are accordingly slightly narrower than the ones included with the denser strips.
To control the LED strip from a microcontroller, three wires from the input connector should be connected to your microcontroller. The LED strip’s ground (black) should be connected to ground on the microcontroller, and the LED strip’s data input line (green) and clock input line (yellow) should each be connected to one of the microcontroller’s I/O lines. The male pins inside the input connector fit the female terminations on our premium jumper wires and wires with pre-crimped terminals. If you are connecting the LED strip to a breadboard or a typical Arduino with female headers, you would want to use male-female wires.
We generally recommend powering the LED strip using the auxiliary power wires. Our 5 V wall power adapters work well for powering these LED strips and a DC Barrel Jack to 2-Pin Terminal Block Adaptor can help you make the connection between the adaptor and the strip. However, you might need a wire stripper to strip off some more insulation from the power wires.
It is convenient that the power wires are duplicated on the input side because you can connect the auxiliary power wires to your 5 V power supply and then the power will be available on the data input connector and can be used to power the microcontroller that is controlling the LED strip. This means you can power the microcontroller and LED strip from a single supply without having to make branching power connections.
If you do not want to use our premium jumper wires to connect to the LED strip’s input, it is possible to make a custom cable.
One option for making a custom cable is to cut off the unused output connector on the last LED strip in your chain. This can then be plugged into the input connector of the first LED strip. The wires on the output and input connectors are 20 AWG, which is too thick to easily use with our crimp pins and housings, but you could solder the wires to header pins.
Alternatively, you can get your own JST SM connectors and make a custom cable using those. The parts you would need to get are the SMP-04V-BC and the SHF-001T-0.8BS, which are described in the SM Connector datasheet from JST. These can be purchased from several places, including Heilind. You will also need some 22–28 AWG stranded wire and a wire stripper. We do not know of a great way to crimp wires onto the JST crimp pins, but we were able to successfully do it using our narrower crimping tool and pliers. (With the wider crimping tool, it is hard to avoid crimping parts of the pin that should not be crimped.) Before crimping, use pliers to bend the outer set of tabs a little bit so that they can hold on to the insulation of the wire. This makes it easier to position the crimp pin and the wire. Next, you should be able to follow the instructions on the crimping tool product page to crimp the wire. After that, you will probably need to squeeze the crimp pin with pliers to get it to fit into the JST plug housing. On the other end of the cable you could make a custom connector using our crimp pins and crimp connector housings, which will allow you to plug it directly into a breadboard or 0.1″ header pins.
Each SK9822 LED draws approximately 50 mA when it is set to full brightness. This means that for every 30 LEDs you turn on, your LED strip could be drawing as much as 1.5 A. Be sure to select a power source that can handle your strip’s current requirements.
The SK9822 has built-in constant current control. For any given colour command, the SK6812’s actual colour and brightness are largely independent of its supply voltage as long as the voltage is between 3.5 V and 5 V. This means that voltage drops caused by the resistance in long power connections are less likely to affect the colour or brightness of the light emitted.
The hue of the light emitted by the SK9822 becomes less red and more green as the 5-bit brightness value is lowered. Also, the SK9822 has some unit-to-unit variation in the brightness of its red channel which can be noticed when the 5-bit brightness value is low but is usually hard to see when the 5-bit brightness value is high.
Multiple LED strips can be chained together by connecting input connectors to output connectors. When strips are chained this way, they can be controlled and powered as one continuous strip. Please note, however, that as chains get longer, they will require more power. If this becomes an issue, you can chain the data lines while separately powering shorter subsections of the chain.
We recommend chains of LEDs powered from a single supply not exceed 180 total RGB LEDs. It is fine to make longer chains with connected data lines, but you should power each 180-LED section separately. If you are powering each section from a different power supply, you should cut the power wires between the sections so you do not short the output of two different power supplies together.
The LED strip is divided into segments, with each segment containing one RGB LED. The strip can be cut apart on the lines between each segment to separate it into usable shorter sections. The data connection is labelled DO or DI, the clock connection is labelled CO or CI, the positive power connection is labelled VCC or 5V, and the ground connection is labelled GND. Each LED in the picture below is at the centre of its own segment; there are lines printed on the PCB silkscreen where the segments can be cut.
These LED strips are controlled through an SPI protocol on the data and clock input lines. The protocol is documented in the SK9822 datasheet (476k pdf), but we describe it below with some modifications that we have found to work better.
The default, idle state of the clock signal line is low, and the data signal is read on each rising edge of the clock. To update the LED colors, you need to toggle the clock line while driving the data line with the value of each bit to send; this can be done through software (bit-banging), or it can be handled by a hardware SPI peripheral in a microcontroller. There is no minimum clock frequency, although using a lower frequency means that it will take longer to update the entire sequence of LEDs (especially when controlling a large number of LEDs), so you will probably want to use the fastest practical clock speed to get the best update rate.
Control signal timing diagram for the SK9822 and APA102C.
The data for each LED is encoded as a sequence of 32 bits (4 bytes) called an LED frame. The first 3 bits of the LED frame should be ‘1’. The next 5 bits are a “global” brightness value (0–31) that is applied to all three colour channels. The remaining 24 bits are the colour values, in BGR (blue-green-red) order. Each colour value uses 8 bits (0–255). The most significant bit of each value is transmitted first. The first LED frame transmitted applies to the LED that is closest to the data input connector, while the second colour transmitted applies to the next LED in the strip, and so on.
To update all the LEDs in the strip, you should send a “start frame” of 32 ‘0’ bits, then a 32-bit “LED frame” for each LED, and finally an “end frame”.
The SK9822 datasheet recommends that the end frame be composed of 32 ‘1’ bits, but we have found this does not actually ensure that all the LEDs will start displaying their new colors immediately. This issue can be avoided by using an end frame that consists of one byte (8 bits) that are all ‘1’, followed by ``5 + n // 16`` bytes (rounded down to the next whole number) that are all ‘0’. For a more detailed explanation, see the comments in the source code of our APA102 Arduino library, discussed below.
If you send fewer LED frames than the number of LEDs on the strip, then some LEDs near the end of the strip will not be updated, and the LED after the the last LED that you sent a colour to will change to black.
For example, to update all 30 LEDs on a 1-meter strip, you should send a 4-byte start frame, thirty 4-byte LED frames, and a 7-byte end frame, for a total of 131 bytes. If multiple strips are chained together with their data connectors, they can be treated as one longer strip and updated the same way (two chained 1-meter strips behave the same as one 2-meter strip).
Each RGB LED receives data on its data input line and passes data on to the next LED using its data output line. The update rate is generally limited only by the speed of the controller; our Arduino library below can update 60 LEDs in about 1.45 milliseconds, so it is possible to update nearly 700 LEDs at 60 Hz. However, constant updates are not necessary; the LED strip can hold its state indefinitely as long as power remains connected.
Note: The minimum logic high threshold for the data and clock signals is not specified in the SK9822 datasheet, so you should consider using level shifters if you want to control these strips from 3.3 V systems. In our tests, we were able to control the LEDs directly with 3.3 V signals, but that is not guaranteed to always work.
To help you get started quickly, we provide an APA102 Arduino library. Our APA102 library supports both the SK9822 and the APA102 (an LED/driver IC that has a nearly identical interface). The library also works with our Arduino-compatible A-Star modules.
Additionally, the DotStar Arduino library and Raspberry Pi Python module from Adafruit should work with these strips since the DotStars are based on similar LEDs. The FastLED Arduino library is another option that focuses on performance and provides advanced functionality like colour correction.
Since the SK9822 is similar to the APA102, most code written for the APA102 should work with the SK9822.
Like the SK9822, the SK6812 used in some of our LED strips also combines an RGB LED and driver into a single 5050-size package. However, while the SK6812 uses a one-wire control interface with strict timing requirements, the SK9822 uses a standard SPI interface, with separate data and clock signals that lets it accept a wide range of communication rates; the trade-off is that two I/O lines are required to control it instead of just one.
The SK9822 provides a 5-bit brightness control that is not available on the SK6812. This feature can be used to dim the LED strip while still retaining 24-bit colour control.
While our SK6812 strips and SK9822 strips are physically very similar, they are not functionally compatible with each other. The easiest way to tell them apart is to look at the strips’ end connectors and the connections between each LED segment: SK6812 strips have three connections (power, data, and ground), while SK9822 strips have four (power, clock, data, and ground).
The SK9822 is very similar to the APA102C used in some of our older LED products, and can be used as a drop-in replacement in many applications. LED products based on the SK9822 and APA102C can be chained together.
The SK9822 and APA102C ICs have different conditions for when to update the colour that is being shown. The SK9822 basically waits until all the LEDs in the chain have received their colors, while the APA102C will start displaying its new colour almost immediately after receiving it. The SK9822’s behaviour is better because it makes it easier to update a large number of LEDs without having perceptible latency. However, if you replace APA102C LEDs with SK9822 LEDs, then, depending on what type of signal you are sending, you might notice that the SK9822 LEDs are late to update. The solution is to make sure that you are sending the correct “end frame” as described above in the “Protocol” section.
The SK9822 has voltage-independent brightness over a wide voltage range, as described in the “Current draw” section, which means that the colors of the LEDs should not be affected by a drop in the supply voltage as much as they are on the APA102C.
The colors generated by the SK9822 look different from the colors generated by the APA102C. In particular, the SK9822’s red channel is relatively less bright, which makes it have a blue-green tint when compared to the APA102C. While the APA102C’s brightness register allows you to control the brightness of each LED independently of its colour, we have noticed that the colors from the SK9822 become less red and more green as the 5-bit brightness value is lowered. Also, the SK9822 has some unit-to-unit variation in the brightness of its red channel, which can be noticed when the 5-bit brightness value is low but is usually hard to see when the 5-bit brightenss value is high.
The SK9822 can be distinguished from the APA102C by visual inspection. The pictures below show what each IC looks like:
|Typical operating voltage:||5 V|
|RGB LED density:||144 per meter|