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Sensors & Transducers

Game play on the go

Alfred Binder looks at how the introduction of a miniature joystick, with ultra-fine control, has brought the computer gaming experience to the mobile phone


onsumers 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 have come to 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 display screen and spoils the visual effect of many games; a trackball’s performance can be degraded by dust or dirt and 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 and 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. The EasyPoint module, designed by austriamicrosystems is being seen as one possible response to this challenge. It is a simple assembly that can be dropped on to a main board and interfacing to the host system’s electronics is straightforward.

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 and the

Figure 3:The 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

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

Figure 2:The EasyPoint module is a simple assembly that can be easily surface- mounted to the main board

module is available in various configurations: the smallest being 8mm x 8mm x 1.5mm.

Figure 1: The EasyPoint module 12 November 2011

How EasyPoint 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

Components in Electronics

processor to read the x,y co-ordinates over a standard I2C 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.

Enabling game play To test the performance of the EasyPoint module in game play, austriamicrosystems modified an HTC smartphone, disabling the gyro sensor input and in its place interfacing to the applications processor a small EasyPoint module with ±1mm displacement.

So could a tiny device with just ±1mm of travel control a game? Pretty well actually. The AS5013 is able to support extreme accuracy, precision and speed.

from the centre to any point at the edge of the sensed area into 128 segments, each with its own co-ordinate. 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 module’s user-selectable frequency was set to its fastest 50Hz speed (a reading every 20ms): the effect was described as being incredibly sharp and responsive, as though the player was using a conventional, handheld gamepad. A low-power device that is easy to interface to an applications processor, devices like EasyPoint have the potential to change the way consumers use any number of small portable devices such as mobile phones. Game play on the go will never be quite the same again!

austriamicrosystems |

Alfred Binder is Marketing Manager at austriamicrosystems AG

plotted, producing the bell-like shapes shown in Figure 3. An internal 8-bit ADC digitises the

field-strength values produced by the five Hall elements, and an internal processing

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

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