S3195227 Sensor report - PROJECT 4
From Physical Programming
Image:Magnetic reed switch.pdf
The device is made of a pair of metal reeds which are placed inside an airtight glass casing. It responds to surrounding magnetic fi elds and offers an on/off output (it is a 2 state sensor). The magnetically charged state will only remain while the magnetic fi eld is present – it re- turns to its original state as soon as it is removed from the area. A basic magnetic reed switch will normally be ‘open’ in its original state and only ‘close’ when a mag- netic fi eld is applied. In order to create a switch that is closed in its natural state, a permanent magnet is placed within the switch. In order to actuate this, a magnetic fi eld is applied (just like before) however it must counter the permanent fi eld already in place. diagram of magnetic reed switch in open position What the device is typically used for? In sports an recreation such as speed sensors on bicycle wheels – A sensor can be attached to the inner fram of the bike (next to the wheel) and a magnet placed on a spoke. As the wheel rotates the magnetic fi eld changes once every wheel rotation to create a uniform pulse which can then be fed back to a electronic board. Both speed, and distance can then be relayed to the user. For secrity for example Door and window sensors in bur- glar alarm systems – A sealed reed switch is installed with a magnet opposing it on a dooway. If the door is opened, the magnetic fi eld around the switch depleats and an alarm is signaled. Within electonics for Mobile Phones and Laptops – When opening or closing the device, the screen lights switches on/off depending on your movements. This is actuated by a magnetic reed switch which is closed in its normal state. When the phone is open, the switch is off and the reeds are separated. As the phone is closed, the contacts on the switch are pushed together, the magnetic circuit is closed and the power is switched off accordingly. Other applications for mangetic reed sensors include: Domestic goods: air conditioners, electric tooth brushes, Washing machines, ovens, etc Automotive: seat belt locks, doors, power windows, ABS brakes, power steering Construction: lifts, conveyor belts
Interfaced with the Arduino micro-controller The arduino is connected to a magnetic reed switch in a similar way to any other switch. The example provided is based on a pushbutton where an output is activated (eg. LED) whenever the input (button) is activated. The arduino also debounces the input to ensure the signal is only read once (otherwise it may be read as multiple, continuous inputs). Various outputs can be created using th arduino that range from Visual, Audio, Mechancal and Physical. Car Lamp Fail Warning, by SatCure 2004 The idea of this is to set up a circuit that interacts with both car lights (left and right). The normal setting is with the switch off, and so when then the lights are off, or they are on (and both are active) the the magnetic fi eld/ current remains con- stant (no change). However, when one of the lights fail, only one current reaches the switch creating a change in mag- netic fi eld, which draws the reeds together. Closing this circuit an LED can be set off to indicate the failure of the car light. Existing Magnetic Reed Switch projects Stationary bike speedometer with Ar- duino and reed switch by reed_switch_speedometer.cpp 21/11/09 The theory of creating a speedometer as de- scribed above was done as a DIY project. Using a magnet that was connected to the outer of the front wheel, a magnetic reed switch is acti- vated to generate the pulse which helps cal- culate how far a person has traveled. The infor- mation can then used to calculate the speed, and even roughly the acceleration of the user.push-button sensor connected to an arduino sketch of circuit for lamp warning system
