Riff
Project Overview
Riff is a build-it-yourself Bluetooth stereo speaker shaped like a little robot wearing headphones, with eyes that pulse to the music. Everything arrives pre-soldered, so there's no soldering iron, no code and nothing to buy: the Allen key and every screw are in the box. Over two weeks you learn how speakers, Bluetooth amplifiers and lithium-ion batteries work, try circuits safely in a browser simulator, trace and check the wiring harness like a real technician, then connect the eye board and assemble the enclosure. You finish with a rechargeable speaker you can pair with your phone and take anywhere. An optional third week shows you how to measure and tune your speaker.
Real-World Applications
Portable Bluetooth speakers
Every portable speaker has the signal chain you build: phone, Bluetooth radio, Class D amplifier and drivers, running on a rechargeable lithium-ion cell.
Headphones and earbuds
Headphones use the same moving-coil drivers, just smaller, and the same impedance and power matching between amplifier and driver.
Factory quality checks
Technicians trace wiring harnesses, tug-test connectors and verify everything before powering up, the same checks you do before Riff plays its first note.
Music-reactive lights
Party lights and stage effects flash with the beat by tapping the audio signal, just like Riff's eyes.
Skills Developed
Project Prerequisites
Before starting this project, we recommend completing these foundational projects:
None: a standalone project, no earlier Zynk Bots experience needed
A phone or tablet with Bluetooth to play music
Recommended
A computer or tablet with a web browser for the simulation labs
Recommended
A USB port or USB charger to recharge the speaker (cable included)
Recommended
Learning Objectives
By completing this project, you will achieve the following measurable outcomes:
Explain how a moving-coil speaker turns an electrical signal into sound
Decode a driver's 4-ohm, 5-watt rating and match it to the amplifier
Handle, insert and charge an 18650 lithium-ion cell safely
Use Ohm's law and a circuit simulator to predict current and see why a short circuit is dangerous
Trace a pre-wired harness against a wiring diagram before powering up
Explain LED polarity and how resistors let the eyes pulse with the music
Make solid connector joints with strain relief and tidy cable routing
Dry-fit, assemble, pair and charge a finished Bluetooth speaker
What's in the Kit
Everything you need to build your Riff, carefully selected and packaged
Micro-USB Cable
USB-A to micro-USB cable. Uploads code to boards with a micro-USB port, like the ESP32, and charges projects such as the Riff speaker from a computer or USB charger.
Speaker Driver (2", 4 Ω, 5 W)
Dayton Audio CE48-4 full-range speaker driver: 2-inch cone, 4 ohms, 5 watts. Riff uses two, one in each headphone ear cup, for real stereo sound. Comes with pre-soldered leads.
On / Off Rocker Switch
A snap-in rocker switch for turning a project on and off. Pre-soldered with male pin headers on the wire ends for easy plug-in to the rest of the circuit.
18650 Rechargeable Battery (2600 mAh)
Rechargeable 3.7 V / 2600 mAh lithium-ion 18650 cell, the standard power source for the portable projects. Drop it into the holder and recharge it over USB through the project's charging board.
18650 Battery Holder (for Riff)
Holds a single 3.7 V 18650 cell, with pre-wired leads that plug straight into Riff's Bluetooth amplifier board.
Bluetooth Amplifier Board (CT14, 5 W + 5 W)
Miniature CT14 Bluetooth 4.2 stereo amplifier board (Class D, 5 W + 5 W). Pairs with your phone and drives two small speakers. Comes with pre-wired speaker and power leads that plug straight in.
Electrical Tape
PVC insulation tape for insulating and tidying wires inside enclosures.
Hex Key (for M3 screws)
Hex (Allen) key sized for the M3 screws — included so the project can be assembled at home without buying extra tools.
Acoustic Damping Material
Soft damping pad that sits behind the speaker drivers to calm buzzes and resonances inside the enclosure. Used in Riff's optional speaker-tuning topic.
Riff — LED Eye PCB
The assembled Zynk Bots eye board for Riff: two white LEDs with their current-limiting resistors and a JST connector, all pre-soldered. The robot's eyes pulse in time with the music.
Riff — Enclosure
3D-printed robot-shaped case for Riff, with headphone ear cups for the two speaker drivers, eye openings for the LED board, and openings for the switch and USB charging port. Reopenable with the included screws.
JST-PH Lead (2-pin, 30 cm)
A 30 cm lead with a keyed 2-pin JST-PH plug. In Riff it connects the eye board to the amplifier so the LEDs share the speaker signal. The key stops it going in backwards.
Course Content
Course Content Coming Soon
This project is being prepared. Course lessons and content will be available once the project is fully published.
Safety Guidelines
Please review these safety guidelines before starting your project
Designed for ages 13+. We recommend an adult is present for the first power-up, when charging the battery, and when using tools.
Lithium-ion battery care
Put the 18650 cell in the right way round and charge it only through the amplifier board's USB port. Never puncture, crush or short it, and stop and tell an adult if it gets hot, swells or leaks.
Disconnect power before handling
Always disconnect power sources and unplug devices before assembling, modifying, or troubleshooting electronic components.
Keep away from water and liquids
Do not use electronic components or tools near water. Keep drinks and liquids away from the work area.
Follow manufacturer instructions
Read and follow all instructions provided with kits and components. Do not exceed recommended voltage or current.
Protect your hearing
Start every test at low volume and turn it up slowly. Don't hold the speaker right next to your ears.
Small parts
Screws and small components are choking hazards. Keep them away from younger siblings and pets while you build.
Related Projects
Continue your learning journey with these recommended projects
Cyclone LED
Cyclone LED is Month 1 of the Zynk Bots path: a reflex game you build and keep. A ring of 45 addressable RGB LEDs chases around the dial, and you press the button to stop the light on the target. Hit it and the game speeds up; miss and the round resets, with your level and high score on the built-in display. You start by trying each component on a breadboard, then in the final week put the whole game together on its own printed circuit board and case. Along the way you write and change the code yourself. No experience and no soldering needed.
Smart Alarm Clock
Smart Alarm Clock is Month 2 of the Zynk Bots path: a real bedside clock you build and keep. A 2.42-inch OLED screen shows the time, date and your alarm, a real-time clock module keeps accurate time, a touch sensor and buttons set the alarm and snooze, and an LED light bar and buzzer wake you up. You move up to a second microcontroller, the ESP32, try each part on a breadboard, then assemble everything on the clock's own circuit board and case. Along the way you write the timekeeping, alarm and scheduling code yourself. No soldering needed.