Game-play on a mobile phone: introducing a miniature ... - ams

Technical Article
<strong>Game</strong>-<strong>play</strong> on a mobile phone: introducing a miniature joystick with ultrafine
control
By Alfred Binder
Marketing Manager, austriamicrosystems AG
Consumers are familiar and comfortable with the user input devices supplied with PCs and games consoles, such
as handheld gamepads with joysticks. They provide the fine control responses that gamers expect.
The circuit and mechanical design of such devices does not, however, translate into the much smaller form factor
of the mobile phone and other small portable electronic products. Yet the increasing computing power and graphics
capability in mobile phones, tablets and so on mean that new technology for a game controller on the mobile phone
is required.
Existing technologies for user input on the phone are far from ideal for gaming:
• a touchscreen provides far less precise control than a cursor-based device, and the user’s hand masks
part or all of the screen when inputting touch commands
• gyro sensors provide an analogue-type response, but moving the gyro means moving the whole device,
including the dis<strong>play</strong> screen. This spoils the visual effect of many games.
• a trackball’s performance can be degraded by dust or dirt. Its response is also unsuitable for gaming, as it
does not support continuous movement or progressive speed control, and does not effectively mimic the
feel of an analogue joystick. Power consumption is relatively high.
• a trackpad (also known as optical mouse, optical finger mouse, optical finger navigation or optical joystick)
suffers from the same disadvantages as a trackball, except that it is immune to dust and dirt.
So a new technology for game control in portable devices is needed.
EasyPoint TM module matches the requirements of the mobile phone environment
austriamicrosystems’ new EasyPoint module (see Figure 1) is a response to this challenge. It is a simple
assembly that can be dropped on to a main board. Interfacing to the host system’s electronics is straightforward.
Page 1 of 4

Technical Article
Fig. 1: the EasyPoint module
The module consists of a mechanical stack incorporating a navigation knob, a magnet and the AS5013 magnetic
encoder IC (see Figure 2). A metal housing provides for stable mounting to the host device’s main PCB. The
module is available in various configurations: the smallest is 8mm x 8mm x 1.5mm.
Fig. 2: the EasyPoint TM module is a simple assembly that can be easily surface-mounted to the main board, with
the AS5013 IC directly underneath the main board
How EasyPoint TM works
The AS5013 IC uses an array of Hall sensors to detect the lateral movement of a magnet above it. The magnet’s
maximum travel is a circle of 2mm radius. Four Hall sensors (C1-4) are placed on a circle centred on the middle of
the AS5013 (see Figure 3). A fifth sensor, C5, in the middle is used to improve linearity response for magnet
displacements larger than ±1mm. The movement of the magnet above the IC generates magnetic fields the
strength of which can be plotted, producing the bell-like shapes shown in Figure 2.
Page 2 of 4

Technical Article
Fig. 3: lateral displacement of the magnet to the edge of its travel produces a change in magnetic field strength that
can be converted into lateral displacement data
An internal 8-bit ADC digitises the field-strength values produced by the five Hall elements, and an internal
processing engine interprets these five values to give a simple x,y co-ordinate representing lateral movement with
a circle of up to 2mm radius. The processing engine eases the designer’s task, because the host processor does
not have to run complex algorithms.
An interrupt signal alerts the host processor to read the x,y co-ordinates over a standard I 2 C bus at a frequency
determined by the developer.
The AS5013, which is the only power-consuming component in the module, has two power modes: a low-power
operating mode, and idle. In idle mode, the device draws only 3µA. In operating mode, the developer can select
from a number of read-out speeds: the higher the frequency of read-outs, the more power the device consumes.
How does a joystick with only ±1mm lateral displacement enable involving game <strong>play</strong>
To test the performance of the EasyPoint TM module in game <strong>play</strong>, austriamicrosystems modified an HTC
smartphone, disabling the gyro sensor input and in its place interfacing to the applications processor a small
EasyPoint TM module with ±1mm displacement.
The demonstration can be viewed online at http://blog.easypoint.com/eng/Latest-Posts/Applications/I-m-able-toshoot-out-2.7-million-words-about-EasyPoint-in-as-little-as-1-minute-48-seconds-impossible.
This shows the tiny
EasyPoint TM device in use in puzzle and car racing games.
Page 3 of 4

Technical Article
How is a tiny device with just ±1mm of travel able to control games The answer is because of the AS5013’s
extreme accuracy, precision and speed. The array of five Hall elements provides a detailed magnetic map of the
circular space in which the joystick moves. The internal 8-bit ADC, which decodes the magnetic field data, divides
the travel from the centre to any point at the edge of the sensed area into 128 segments, each with its own coordinate.
When the device is configured to measure the maximum ±1mm displacement, this means it can track
movements of just 7.8µm.
In itself, this detailed reading will not provide a sharp response to the user’s input unless the device updates the
application fast enough to track the real-time movement of the joystick. In the HTC phone test, the EasyPoint TM
module’s user-selectable frequency was set to its fastest 50Hz speed (a reading every 20ms): the effect was
incredibly sharp and responsive, as though the <strong>play</strong>er was using a conventional, handheld gamepad.
A low-power device that is easy to interface to an applications processor, EasyPoint TM has the potential to change
the way consumers use any number of small portable devices such as mobile phones. <strong>Game</strong> <strong>play</strong> on the go will
never be the same again!
A video demonstrating the EasyPoint TM module is available at http://blog.easypoint.com/eng/General/EasyPoint-
Video . Developers can order the EasyPoint TM AS5013-DB Demoboard online at www.austriamicrosystems.com.
Page 4 of 4