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Revision as of 18:53, 8 November 2007

taboo board games video gallery window media web marketing business to business nursing shortage nes emulator for the psp 1968 presidential elections surgical wound dressings stock exchange never compromise gray matter 2 in kine bartending schools fort worth med scalp echo glen park association ga realtor renault kangoo iis help russian bolsheviks auto napa store online marketing manager jobs listen to music swedenborg burners what is bpo fat girl free math worksheets oldpussy cheap azithromycin institue of canadian banker e commerce site builders cheap azithromycin ultimo polvo business phone numbers retin winnie the pooh pictures online casino credit card friendly grants for electric ace true value hardware love hina jelqing video ont car rental the london fog sprint ringtones kick it lyrics misleading statistics haylie duff pontiac wildcat venice hotels discounted 2007 nissan 350z cell phone directory solar passive building design the walkie talkie man lipitor side effects ceap airline tickets albin dildo sex coins hyundai cars northwestern university graduate school of business levothyroxine gifts for man system not booting up my all lyrics mariah carey free symantec antivirus download lesson london ontario swimming number order process animated under construction speaking trumpet the nervous system and the endocrine system mp3 ringtones free zoom text lawyer partnerships picture of family coat of arms discount airline ticket mature asian lake superior campground symptoms of low testosterone demoral self storage hollywood flea market animation no limit poker free currency rate number of religions in india aol music free web cam chat room instant lingo message syphilis home a womans got the power as tom sawyer plays nutrition michael schwab page sun flower clip art intellectual property in internet insurance for family entertainment center weird world record lavasoft adaware link woman hater jokes porsche 911 turbo latin ringtones kinetic assay urbana schools pinay big numb3rs season premiere architecture network speed pro performance parts panic attack breathing exercises indoor gardening seattle article graphs ser jobs for progress inc earth temperature profile order diazepam ministry of education ontario government alcohol symptom withdrawal discount fioricet master degree economics sheffield utd tickets edit plus software download pacman pics american girl and girls inc awareness site away message quotes average factor rating weighted service magazine plastic wrap made of keith nicholls voice ringtones adult character child development in 2002 breaking in news what is qcd port authority new york address free downloadable ringtones aula magna actress indian nude picture south aol technical help phone number america home cooking cook book ib 12 agency empowerment people x scale processors quick snooker games work recruitment agency long range wireless access points local katrina relief efforts lining of heart chambers free sonyericsson ringtones agreement confidentiality employee atv accessaries abs pipe prices usa network dead zone whats going on in there lebanese media links plato contributions northwestern university in evanston il lightscribe dvd drives rainbow six 3 for gamecube insurance terminology definitions james bond girls images stools for kitchen island united airways phone number indias hottest girls million dollars picture rum cake recipe alaska governor state time two sell mortgage notes rental cars cheapest discount didrex pet abuse laws musician ri wedding iden phones motorola prepaid phone call set canceled modern rock philadelphia sailing show world map of algeria lips kissing entry level it resume expressiveness alcatel ringtones airway us visa rover north america linked with accounts accounts payable positions wild bunch film distribution suggest a web site pavement lyrics phoenix az temperatures sbs 2003 fax server map type true ringtones i heard em say lyrics sprint car builder what type of fruit is a love apple konie pl 1979 floyd pink wall asian guy fuck kick boxing schools sodomy laws {| align=right |- | Relay |} Description:
A PIC can't source more than 25mA, so how do I turn on/off a light bulb? With a relay!

Relays are those large black boxes that go 'click'. There is a coil inside. When current flows through the coil a magnetic field causes the the internal paddle to move postions. This paddle usually carrys large currents or large voltages.

Most relays have various ratings. We'll start with the coil voltage. '12VDC' for example means that the control coil requires 12V DC for the unit to switch the paddle. The other rating you'll see is '10A'. This refers to the amount of current you can run through the control paddle contact (not the current through the coil). So a 10A relay can handle a load of up to 10A- less than 10A is no problem. What happens if you try to run more current than the max? Well, it will probably work, but at higher currents the internal sparking will tend to burn the contacts. The paddle can potentially spot-weld itself to the contacts in extreme cases.

There are sealed and vented relays. Vented relays tend to run a bit cooler, but are more suceptible to gunk getting into the moving parts.

There are many configurations based on the circuit you need to control. DPDT (double pull double throw), SPDT (single pull double throw) are two of the most common. View the equivalent circuits in the mfg's datasheets to get an idea of how they work.

Relay circuit setup:
When switching large loads, you can get something call fly-back current. These are surges of current when a device is kicked on/off (imagine when the lights dim when you turn on the microwave). Well if it's large enough or often enough, these surges can really kill your board's power supply. The fly

Example Relay Circuit

Many microcontrollers cannot source enough current to feed the control coil. So Q1 is any old BJT (2N3904 is a good one) to turn on/off the relay. The diode 1N4148 (simple, cheap, can handle ~200mA current) is there to supress any fly-back current from entering the main power supply. Be sure to watch how you polarize your diode.


SFE Footprint Library

There are various footprints available. Always be sure to do a 1:1 printout of your board and matchup the physical relay to the printout before PCB fab. Sometime the manufacturers list recommended footprints from the bottom view which can lead to mirrored and incorrect FPs.

Manufacturer Info:

Supplier Info:
Digikey part # : G5Q-1-DC12
Single Piece Price : $2.25

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