The Sonic Bow Tie is an electronic kit for engineering geeks with a sense of humor, available now at the BMOW store. The circuit board is shaped and sized like a real bow tie, and is colored classic black. Once assembled, a piece of ribbon can be anchored through the board’s central mounting holes, making it easy to wear at the collar of a dress shirt or tied around a ponytail.

Wearable computing is the latest trend, and you’re at a party listening to some hipster brag about his new iWatch. “Hmm, not bad…” you say. Then you casually reach for your collar and switch on your SONIC BOW TIE 3000. Wham! Your audience is blown away by your neck-based audio-visual spectacle. Lights flash and a digital melody bursts forth. With a wave of your hand you exert theremin-like controls, shifting the pitch of digital warbling at will. The onlookers cry out “WHAT IS THIS SORCERY?!”

Attending a wedding soon? Graduation ceremony? Audience with the pope? The Sonic Bow Tie 3000 is the perfect geek accessory for any formal occasion.

Ladies: are bow ties not your style? Turn it around, and make a dazzling electronic ponytail holder perfect for your next Maker Faire presentation or inaugural ball.

While a pair of jumbo 10 mm LEDs flash, the bow tie repeats a simple 8-note digital melody, alternately soothing and annoying those around you. A center mounted photo-resistor acts as a light sensor, biasing the melody’s pitch. Turn your body towards the light, and the pitch shifts upward. Turn away or shade the sensor with your hand, and the pitch shifts downward. Fortunately there’s also an on/off switch, for when your friends threaten you with bodily harm if they hear one more second of that #*&($#@!

The kit contents are simple through-hole parts, so it’s easy to solder even for a beginner. Build one for yourself, or get a kit for your kid/student/friend and assemble it together. Who wants the boring LED blinker in a typical learn-to-solder kit, when you could have a crazy bleeping sonic bow tie theremin?

  
How it Works

The fun begins with a classic 555 timer, configured in astable mode to generate a square wave with a frequency around 1000 Hz. This is IC1A as shown in the circuit diagram. The exact frequency of the square wave is determined by the values of C3 and R1. R1 is a photo-resistor whose resistance varies with illumination. This causes the timer frequency to shift up or down in response to changing light conditions. When connected to a speaker, it creates a continuous tone whose pitch changes depending on the light.

A continuous tone isn’t very interesting, but we’re not done yet. A second 555 timer is also configured in astable mode, generating a square wave at about 4 Hz (250 millisecond period). This is IC1B in the circuit diagram. A pair of LEDs are connected to this square wave output, causing them to blink 4 times per second.

The 4 Hz signal is also used as the clock input to IC2A, a 4-bit binary counter. The circuit uses a CMOS CD4520 binary counter chip, instead of a more common 7400 series binary counter, because the CD4520 can tolerate supply voltages up to 20 V. This makes it possible to run the entire circuit directly off a 9 V battery, with no voltage regulator.

The lowest three bits of the current count are connected through series and parallel resistors to the control voltage input of the first 555 timer. This biases the continuous tone up or down in pitch, with a new bias voltage appearing every 250 milliseconds when the counter advances. The result is a repeating melody of eight notes, whose relative pitches are set by the binary counter, and whose overall pitch can be shifted further up or down by changing illumination at the photo-resistor.

 
Wear and Usage

To wear the Sonic Bow Tie 3000 around your neck, drop the battery inside your front shirt collar and allow it to hang loose by the clip wires. Normally this is all that’s needed to anchor the bow tie at your collar. If desired, a ribbon or shoelace can be passed through the two holes in the center of the circuit board, and tied around your neck.

To wear the bow tie as a ponytail holder, pass a ribbon through the center holes, and tie it around your hair at the base of your skull. The battery can be dropped inside the rear of your shirt collar, or hidden inside your hair.

The pitch bends of the digital melody are controlled by the level of illumination on a photo-sensor mounted at the tie’s “knot”. The bow tie works best indoors, in a room with moderate lighting. To shift the melody’s pitch higher, move closer to a light source, or turn the bow tie to face directly towards the light. To shift the melody’s pitch lower, move away from the light source, or shade the photo-sensor with your hand. By waving your hand rapidly above the photo-sensor, a warbling vibrato effect can be achieved. Is it science, or sorcery?