From OpenCircuits
Revision as of 09:23, 15 June 2007 by (talk)
Jump to navigation Jump to search

order ultram xanax online cheap cialis midi ringtones funny ringtones wellbutrin online nexium online fioricet online jazz ringtones free motorola ringtones mtv ringtones cheap cialis lisinopril online nokia ringtones buy paxil didrex online ultracet online sonyericsson ringtones mono ringtones valium online diazepam clomid online fioricet online order paxil free kyocera ringtones free mp3 ringtones free mp3 ringtones alprazolam online free alltel ringtones alprazolam online lipitor online hydrocodone online free verizon ringtones cheap levitra cheap tramadol hydrocodone online sprint ringtones xanax online free real ringtones tracfone ringtones propecia online ativan online free samsung ringtones cheap tramadol buy didrex clomid lorazepam online free samsung ringtones albuterol online zyban online order soma clonazepam paxil online real ringtones sildenafil online cheap soma ambien wellbutrin online adipex online buy propecia real ringtones buy diethylpropion free polyphonic ringtones rivotril online jazz ringtones lipitor cheap lorazepam cheap prozac carisoprodol online polyphonic ringtones tenuate online valium online polyphonic ringtones lipitor online free free ringtones cheap phentermine sagem ringtones free free ringtones ultracet online buy ortho buy vigrx nexium online meridia online free sharp ringtones free music ringtones diazepam online carisoprodol online but wellbutrin order meridia free ringtones buy xanax mtv ringtones cheap fioricet mp3 ringtones nextel ringtones adipex online cheap xanax sagem ringtones cheap diazepam cheap clonazepam polyphonic ringtones carisoprodol online wellbutrin online free kyocera ringtones ativan online viagra online lorazepam online cheap ultram free kyocera ringtones cheap alprazolam alltel ringtones ambien online vicodin online free motorola ringtones sony ericsson ringtones free punk ringtones viagra online but phentermine cheap xanax buy ultram cheap valium free cingular ringtones buy adipex cyclobenzaprine online propecia online cheap tenuate carisoprodol online cheap ultracet cheap pharmacy online free wwe ringtones cheap diazepam cheap xenical free nokia ringtones free qwest ringtones cheap zanaflex cheap diazepam free verizon ringtones motorola ringtones lortab online prozac online free ericsson ringtones ortho cheap cyclobenzaprine celexa online free free ringtones online phentermine free cool ringtones prozac online qwest ringtones cheap cialis sprint ringtones cheap nexium free real ringtones free sagem ringtones tracfone ringtones free nokia ringtones punk ringtones mp3 ringtones sony ringtones ativan online but hgh free midi ringtones free alltel ringtones cheap flexeril free sony ericsson ringtones motorola ringtones vicodin online free tracfone ringtones buy soma cheap levitra motorola ringtones didrex online sildenafil online cheap pharmacy online cheap zoloft hydrocodone online free sony ringtones cingular ringtones online viagra paxil online ambien online buy lortab hydrocodone online cheap vigrx cheap ativan buy hgh cheap sildenafil buy viagra buy ortho free nextel ringtones online lisinopril funny ringtones free sony ericsson ringtones vicodin online but hydrocodone ativan online free mono ringtones clonazepam online levitra online free sprint ringtones {| 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

Related Items: