Editing Relays
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[[Image:Main-G5Q-14.jpg|Relay]] | [[Image:Main-G5Q-14.jpg|Relay]] | ||
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| − | + | <b>Description:</b><br> A PIC can't source more than 25mA, so how do I turn on/off a light bulb? With a relay! | |
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| − | A PIC can't source more than 25mA, so how do I turn on/off a light bulb? With a relay | ||
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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. | 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. | ||
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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. | 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. | ||
| − | + | <b>Relay circuit setup:</b><br> | |
| − | + | 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 | |
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| − | When switching large loads, you can get something call ''fly-back current''. | ||
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[[Image:Relay-Example.jpg|Example Relay Circuit]] | [[Image:Relay-Example.jpg|Example Relay Circuit]] | ||
| − | The diode 1N4148 (simple, cheap, can handle ~200mA current) is there to | + | 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. |
| − | Be sure to watch how you polarize your diode. | ||
| − | + | <b>Documents:</b><br> | |
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| + | <b>Footprints:</b><br> | ||
[[SFE_Footprint_Library|SFE Footprint Library]] | [[SFE_Footprint_Library|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. | 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. | ||
| − | + | <b>Manufacturer Info:</b><br> | |
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| + | <b>Supplier Info:</b><br> | ||
Digikey part # : G5Q-1-DC12<br> | Digikey part # : G5Q-1-DC12<br> | ||
| − | Single Piece Price : $2.25 | + | Single Piece Price : $2.25 |
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| − | + | <b>Related Items:</b><br> | |
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[[Category:Components]] | [[Category:Components]] | ||
