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TECHNICAL DESCRIPTION OF THE PROTOTYPE SYSTEM

Material
The prototype system is based on two different electrical toothbrushes – Braun’s Mickey Mouse Oral-B and Colgate’s Motion Kids. The choice of these two toothbrushes is quite straightforward. They are both very appealing to children. The Braun toothbrush is delivered with an induction type battery charger – a rechargeable toothbrush is more preferably used compared to one with replacement batteries (like the Colgate toothbrush). However, the Colgate toothbrush offers greater possibilities when it comes to modifying it. So we decided to combine the two toothbrushes when building the prototype.

All the existing electronics in the Colgate toothbrush was removed and replaced with a circuit board containing the following:

1 x NetMedia’s BasicX-24 microcontroller
1 x Adcon’s addLink radio module
1 x Memsic MXR2999 accelerometer
1 x IB Technology Micro RWD RFID reader/writer

Moreover, the induction charger module of the Braun toothbrush was taken out and placed in the Colgate toothbrush along with the other electronics. Since the original rechargeable battery was too bulky to fit in as well, it was replaced with a thinner 1.2 Volt GP NiMH prismatic battery. A MAX1675 step-up circuit was also added to supply the CMOS circuits with 5.0 Volt.

The charger of the Braun toothbrush was also customized with the following components:

1 x NetMedia’s BasicX-24 microcontroller
1 x Adcon’s addLink radio module
2 x TDA7052 audio amplifiers

The charger features an AC to AC converter (for induction charging) which outputs 7.0VAC. To avoid having an additional power supply, a simple DC rectifier and a 5.0 Volt regulator was coupled onto the AC output.

At an early stage in the project we considered equipping the base station (i.e. the charger) with some kind of sound producing circuit. Limited time and difficulties in finding an appropriate device forced us to look for an alternative solution. A laptop with a soundcard and a java-based midi player was found well suited for this task.


How the toothbrush works
To describe how the different components of the toothbrush interact, one could say that the microcontroller receives input from the RFID reader and the accelerometer. This information is sent to the base station through the radio module.

The accelerometer is the core component of the toothbrush. With this device it is possible, after some calculations, to determine both the speed of the toothbrush (movement back and forth) and how it is oriented (angle relative to floor).

The RFID reader is in itself a quite complex device. It works by sending out a radio frequency signal, which, when received by an RFID tag, will ‘detect’ the tag’s unique identification number. The tag is actually a radio transmitter itself which is charged with energy from the reader’s radio signal. When charged with enough power, the tag will send its identification code back to the reader.

The antenna of the RFID reader is hidden in the head of the toothbrush. RFID tags on the toothpaste tubes are read when the user applies toothpaste onto the toothbrush. The range of the reader in our application is set to a few centimeters. This range is deliberatly chosen, since it’s only intended to read the tags when applying toothpaste.

The RFID technique allows mapping of different toothpaste tubes to various music genres. Once a certain toothpaste (tag) has been identified, a random song of that genre will be selected by the software in the laptop.

RFID codes and accelerometer values are received by the microcontroller and passed on to the radio transmitter in the toothbrush. The base station, which is equipped with a radio receiver, receives this data and passes it on to the laptop.


How the base station works
The base station acts a server to which the toothbrush is a client. It receives data from the different sensors in the toothbrush and uses this information to (1) select music to play during use of the toothbrush, and (2) alter the tempo and pitch of the music currently played.

When the toothbrush recognizes an RFID tag, the base station will immediatly receive the tag’s identification code and transfer it to the laptop. The server application running on the laptop will then select and play a midi file from a group of files associated with the specific tag. Midi files are selected randomly in a non repeating manner.

The readings from the accelerometer are passed to the laptop in the same way as the RFID tags. The accelerometer outputs X and Y axis values simultaneously, which are processed with different mathematic formulas to determine orientation (angle) and speed (relative movement) of the toothbrush.

The orientation of the toothbrush is associated with pitch of the music. Holding the brush upwards (i.e. brushing your upper teeth) causes a pitch one octave higher. Lowering the toothbrush 90 or 180 degrees (i.e. brushing the front of the teeth or the lower teeth) from this position will lower the pitch either one or two octave steps. The altering of the pitch is done in real time by altering the midi notes currently played.

The speed of the toothbrush is used to set the tempo of the music. Slow movements of the toothbrush will slow the music down accordingly. Brushing really slow can even stop the music. Faster movements will increase the tempo. The altering of the tempo is simply done by changing the length of each note currently played.

The audio signal from the laptop is the fed to the amplifier in the basestation, which amplifies and sends audio to the speakers. The volume level can be adjusted by the user with a potentiometer located on the base station.


Click here to see a
Block diagram (.pdf) over the toothbrushs technique.