In this Teardown Tuesday, we will look at the PCB that makes up the core of the Freedrum system.

### Introduction

Drum kits are essential in many genres of music, ranging from classic rock and roll all the way to modern dubstep. While many use drum machine VST packages (virtual studio technology), there are millions of musicians who use real drum kits and for good reason. While drum kits are a great instrument they are not the most portable kit. This is where a Kickstarter project, Freedrum, hopes to change just that! Their small device is attached to either drum sticks or feet (or even both) and allows you to play drums wherever you are.

Let's crack them open!

### The Main PCB

The main PCB consists of a few ICs and surface mount components. The PCB clearly demonstrates production techniques that are helpful for low-volume production such as placing all surface mount components all on one side.

Using all surface mount helps to keep production costs to a minimum as there is no hand soldering needed. The use of all surface mount parts on one side also means that, once all the parts are placed onto the PCB, the whole board is soldered in one go using a reflow oven.

##### The Freedrum PCB

The underside of the PCB shows the use of a large ground plane which helps to remove unwanted electronic noise in signal and power wires. The use of the ground plane and stitching via also helps with compliance with EMC regulations that are imposed by CE and FCC.

One other interesting feature of the Freedrum PCB is how, instead of being V-Scored, the PCB is milled with drilled tabs. While the tabs, themselves, are a dead giveaway to milling, there is one other subtle clue, the angled cut marks on the board edge. This shows the tool rotation as the milling bit cut out the PCB border.

### Bluetooth Control

The Freedrum can connect wirelessly to tablets, computers, and even Android devices using Bluetooth. The IC responsible for this is the N51822QF, which is a Bluetooth system-on-chip produced by Nordic Semiconductor.

The SoC is built around a 32-bit ARM Cortex M0 CPU which 256kB flash ROM, 32kB RAM while integrating a 2.4GHz Bluetooth protocol stack. The chip, itself, has an event-driven API which is crucial in embedded designs as signals that can arrive at any time need to be processed immediately (for low latency).

### The Main Controller

The main controller for the Freedrum device is the INVESENSE MPU-6050 which is a microcontroller with inbuilt 3-axis gyroscopes and 3-axis accelerometers.

The advantage of such a controller is the use of inbuilt sensors that removes the requirement of external sensor ICs which can drive up production cost, increase PCB complexity, and use precious PCB space. The controller also has generic modules such as I2C and SPI so other sensors and devices can easily be connected to the system.

### Wi-Fi Antenna and Other Components

Interestingly, the Freedrum PCB uses a custom PCB antenna trace which makes commercialization more difficult. A complete Wi-Fi module that contains its own antenna should already be certified for EMC standards which means that it can mostly (take it with a pinch of salt) be ignored and does not require testing.