What is it?

This is Texas Instrument's LP55231 Programmable LED Driver and three common-cathode rgb leds on a small board designed to be mounted directly onto a Teensy 3.X or used in a standard breadboard with any microcontroller.

From the data sheet: "The LP55231 is a 9-channel LED driver designed to produce lighting effects for mobile devices. A high-efficiency charge pump enables LED driving over full Li-Ion battery voltage range. The device is equipped with an internal program memory, which allows operation without processor control. The device has ... three Independent Program Execution Engines, 9 Programmable Outputs With 25.5 mA Full-Scale Current, 8-bit Current Setting Resolution and 12-bit PWM Control Resolution."

The LP55231 comes in a 4 mm x 4 mm QFN package and requires just four passive components, so the complexity is low and the size can be small.

Input voltage ranges from 2.7 to 5.5 V, and the standby current is just 200 nA which makes battery operation for portable, wearable applications feasible.

Why did you make it?

I have had good experience with led drivers, especially with Holtek's HT16K33 led driver. The thing I like about the HT16K33 is that up to 128 leds can be driven with just power, ground and I2C and without one current limiting resistor. This really saves in complexity, but the HT16K33 is a rather large chip and not really suitable for wearables or small portable projects. Some people use PWM from microcontrollers to drive leds, but most microcontrollers have a limited number of PWM-capable pins and adding a GPIO expander just adds complexity. I wanted something that could be independent of a host microcontroller, is very small for portable, wearable applications, requires few components, and is powerful yet easy to use. I found the nearly perfect solution in the LP55231 programmable led driver. I designed this simple board as a test bed to learn how to program the driver and control the leds. Getting simple patterns via host I2C control took me less than an hour after I assembled the first board, and I am using this board to learn how to use the programming and diagnostic tools TI makes available for users of this chip.

I plan to make some Christmas ornaments to give to friends that use one or more of the LP55231 and some leds driven by a coin cell battery to hang on their trees. I am also using the chips for more practical applications to provide visual feedback based on sensor data. Feedback by blinking an led is fine when you are getting started, but intensity variation and color change in response to sensor data offers better feedback information to users of your application. The LP55231 makes such feedback practical and easy to implement.

What makes it special?

This is a small, inexpensive board you can use to get familiar and gain experience with this versatile new technology. Like many Pesky Products, it is designed to mount directly onto a Teensy 3.x, but it can also be used in a conventional 0.1" breadboard for testing and prototyping.

I wrote a basic sketch to initialize the LP55231, set the led current and send PWM commands to the rgb leds in interesting patterns. This shows how to get started, but the chip is so versatile that there is no end to the patterns (ramping, pulsing, responding to external stimuli, etc) that are possible. The limit is your imagination!

Order the pc boards from OSH Park and assemble your own, or buy the fully assembled and tested boards from me and see what sophisticated visual feedback can add to your application!