What is it?

This is a programmable sound reactive board with 12 full-color Neopixel leds, specially designed to be used as a wearable device or a gadget for other audio systems.

You can see how it works in this video

The main MCU is the mainstream STM32f070F6P6 32-bit ARM Cortex-M0 operating at 48MHz, with 32Kb of FLASH memory and 6Kb of RAM. It can be programmed via Serial Wire Debug (SWD) port with an STLink programmer.

For audio input, it uses an omnidirectional electret microphone of 6x2,7mm with -50dB sensitivity working at frequencies from 100Hz to 10KHz. The signal is amplified with an op-amp that features rail-to-rail input and output, and the gain is controlled with a variable resistor so you can adjust the sensitivity according to the audio volume being heard. Please note: SMD variable resistors are fragile devices, so turn it gently ;)

For the LEDs, it uses WS2812 chips (aka Neopixel) in a 5050 package. You can select between two different versions:

• WS2812B: A full brightness led with 30mA current consumption at full white brightness.
• WS2812C: Operating Current of 5mA per color, the brightness reduced to one-third of the original, it’s preferred for portable electronic devices.

The overall max consumption is 380mA for WS2812B and 180mA for the C version, but keep in mind that this is for full brightness white color. With typical application these values are much smaller.

There is a LDO voltage regulator to adjust input voltage to the 3.3V required by MCU. It accepts a max input voltage of 5.5V, but it must be down to a range of 3-4V for proper operation, so a LiPo one-cell (1S) is a good option. Also, a Schottky diode protects the system from reverse polarity.

Lastly, the board exposes I2C pins, so you can add additional sensors or peripherals. Also, there is a button connected to GPIO PA7, used for switching between display modes and change the brightness intensity (more info in github repo). The two M2 mounting holes can be used to attach it to other boards or to sew the plate.

It comes fully assembled (except pin headers for SWD and I2C; for input power you can choose the configuration), tested, and pre-programmed with the example available on the source code link. You only need to power it up to start enjoying it.

Why did you make it?

Neopixel leds are very striking, especially when used with audio. I need to have a plate small enough to be incorporated into portable devices or wearables: bracelets, baseball hats, backpacks, or simply as a complement to portable audio devices or desktop gadgets.

What makes it special?

The round plate has 45x45mm with a thickness of 1mm (5mm assembled), making the final assembled board weights only 5 grams. The are many options available on internet in a form of led rings, but is hard to find an all-in-one board like this one.