Lit Hand Signals


A device with a set of bright LED's that attaches to the hand or wrist and automatically detects its orientation to indicate a turn or stop. Using one on each arm can allow for clear night-time signaling with the standardized hand singals shown below.


The device consists of a small rechargeable battery and charging circuit, a micocontroller, a row of addressable RGB LED's, and a 3-axis gyroscope + accelerometer combo board.

I programmed the device to respond with light patterns based on the rotation of the arm. Since hand signals are relatively standardized, each signal could have a corresponding light pattern. To clearly indicate the direction of an intended turn, the demo video shown above shows a light pattern movement that epresses leftward movement. If the hand were to be raised up or down, a different color or pattern could be used. Another device on the other hand could be used for extended arm signaling.

With a watch-style band, it can easily be strapped to the wrist as shown below.


There can be many uses for an individually addressable light bar with a microcontroller and inertial measurement unit. I initially came up with the idea so that I use them for extra visibile turn signals while riding my DIY electric longboard during the night. It doesn't only apply to e-skating though. With simple changes to the code, a large variety of uses become available. Applications in bicycling safety, e-scooting safety, and other personal electric vehicle safety come to mind.

They aren't necessarily limited to bodily attachment either. With a simple code change, it could function as an add-on brake light that one can attach to a portable transportation unit by sensing deceleration in a certain axis. They can even act as simple and fun glow lights that anyone can attach to their personal portable transportation vehicles.

Specific modes for several use-cases are detailed below.

Skating: I designed and built a set of two "lit hand signals" for my own use while riding my DIY electric longboard. Typically, my hands are at my side while skating, and when I want to indicate a turn or lane change, I hold my respective arm outward. Take a look at the diagram above to see the orientation of the gyroscope with respect to gravity with each standard position or signal. For skating, the "arm at side" and "stop" signals are indistunguishable given the direction of gravity. If you have read the project page for my DIY electric longboard, you might remember, however, that I designed built-in brake lights in the rear electronics housing that taps into the controller input signal, so braking signals on the hand would be redundant for this use-case anyways. Given this information, a "skating" mode only needs a single light pattern that is activated when the respective arm is out to indicate turning or lane changing. With the orientations shown in the diagram, the 'lights on' condition is (rouhgly) as follows, where g is the acceleration due to gravity:

Left hand: measured acceleration = [-g, 0, 0]

Right hand: measured acceleration = [g, 0, 0]

Biking/Scooting: When biking or scooting, each regular position has a unique vector relative to gravity (assuming the vehicle uses straight handlebars), where "arm at side" is not considered a "regular" biking position.

Arm at side: measured acceleration = [0, g, 0]

Right signal, left hand: measured acceleration = [0, -g, 0]

Right signal, right hand: measured acceleration = [g, 0, 0]

Left Signal: measured acceleration = [-g, 0, 0]

Stop: measured acceleration = [0, g, 0]

Riding: measured acceleration = [0, 0, -g]

Add-on brake lights: If the sensor detects deceleration in forward facing axis, the brake light will turn on until it senses acceleration again. If the z-axis is is forward facing with the x-axis pointing up, the x-axis will always measure roughly -g most of the time and the z-axis will measure the acceleration of the vehicle.

if acceleration(z_axis) < (0 - tol)

turn lights on

if acceleration(z_axis) > (0 + tol)

turn lights off