Laser mouse
A laser mouse is an optical computer mouse that uses a laser diode with coherent light to illuminate the contact surface . This distinguishes it from conventional optical mice, which use a light-emitting diode (LED) that usually works in the visible red range as a light source.
history
The first model of a laser mouse, Logitech MX 1000 Laser , introduced Logitech ago in the fall of 2004. This achieved an image processing speed of 5.8 megapixels / second at a resolution of 800 cpi (these values correspond to those of the previous MX500 and MX700 mice with conventional optical scanning).
technology
Laser mice were developed because optical mice with LED light sources have difficulties in determining the direction and speed of movement on unstructured, transparent or reflective surfaces. Thanks to the speckle effect, which is particularly evident with coherent light, laser mice can also cope with smooth surfaces such as metal or polished wood. The speckle effect ensures a high contrast even on slightly structured surfaces.
In the laser mouse, an inexpensive surface emitter (VCSEL) is usually used as the laser diode , the laser beam of which is expanded by an optical lens in the housing and thus a small area of a few millimeters in diameter is illuminated under the mouse. Immediately next to the laser diode in the housing is the optical receiver, which receives the light reflected from the surface via a lens system. Depending on the type, several 1000 individual images (frames) are detected per second; values up to 7000 images per second are common, which are processed by subsequent signal processing in a digital signal processor (DSP) optimized for this application . The DSP calculates the movements in both axes from the sequence of individual images and their changes and transmits this information to the PC.
The resolution - this is specified in counts per inch (cpi) and corresponds to the number of pixels that can be captured per 2.54 cm - varies depending on the type and is between 200 cpi and 8000 cpi.
Most laser mice are built with sensors from Avago Technologies, a former subsidiary of Hewlett-Packard that also holds many key patents for optical mice. Cypress Semiconductor has also recently started offering a chipset for laser mice that uses a different method of image analysis and thus bypasses the AvagoTech patents.
safety
For reasons of cost and efficiency, an infrared laser diode is used in laser mice . The laser radiation - wavelengths around 848 nm are common - cannot be perceived by the human eye, which can pose a safety risk. In order to avoid damage to the eyes from the laser - with invisible infrared light, the eyelid-closing reflex does not work as a protective function for the eye - only lasers of laser class 1 are used, i.e. the intensity of the laser radiation is so low when looking at it that no eye damage occurs . In addition, there are precautions in the mouse electronics to limit the power of the laser diode upwards and to switch it off in the event of technical defects.
literature
- Peter W. Milonni, Joseph H. Eberly: Laser Physics . John Wiley & Sons, 2010, ISBN 978-0-470-40970-1 , Chapter 15: Diode Lasers and Optical Communications.
Web links
Individual evidence
- ↑ a b Datasheet: ADNS-6010 - Laser Mouse Sensor. Corporate font: Avago Technologies, accessed March 31, 2017 .
- ↑ http://www.weltderphysik.de/thema/hinter-den-dingen/elektronische-geraete/optische-computermaus/lasermaeuse/ Dörte Saße: Laser mice and other rodents in the world of physics / science current, December 15, 2008, accessed on July 26, 2017
- ↑ AN 5088: Laser Mouse Sensor Eye Safety Calculations. (No longer available online.) Company font Avago Technologies, formerly the original ; accessed on March 31, 2017 . ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
