01-06-2012, 11:17 AM
INFRARED PAIR: TRANSMITER: Remote Control
INFRARED PAIR TRANSMITER Remote Control.doc (Size: 53.5 KB / Downloads: 42)
Infrared (IR) light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.7 micrometres, and extending conventionally to 300 micrometres These wavelengths correspond to a frequency range of approximately 430 to 1 THz. They have thermal energies in them. Near infrared" light is closest in wavelength to visible light and "far infrared" is closer to the microwave region of the electromagnetic spectrum. The longer, far infrared wavelengths are about the size of a pin head and the shorter, near infrared ones are the size of cells, or are microscopic. the primary source of infrared radiation is heat or thermal radiation, any object which has a temperature radiates in the infrared. Shorter near wavelength in used in the remote controls.
RELAYS:
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal.
The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations.
A relay is a switch which is operated by electricity. It is usually electromagnetic device which has coil. When this coil is supplied with power, a magnetic field created and will operate mechanical switch. There are solid state relays which do not have moving parts but are very expensive compared to small mechanical relays. Pictures in this page shows typical small electro mechanical relay. Relay is used when we need to handle high voltages and currents through microcontroller operated system.
Relay coil's current requirement is usually more than 100mA (for small relay about 100mA) and microcontroller cant supply this much of current to relay by it self. So as shown in following schematic diagram, we have to use transistor to handle this current requirement. Base pin of NPN transistor used here is connected to ground pin via resistor to make sure that relay will stay off when microcontroller does not output +5V to transistors base. This will make sure only logic 1 on microcontroller pin will activate relay. It is better to use Darlington transistor to handle current requirement for relay, because darlington transistor can handle more current than single transistor.
CRSTAL:
Good Frequency Accuracy and Good Stability Over Temperature.
The majority of clock sources for microcontrollers can be grouped into two types: those based on mechanical
resonant devices, such as crystals and ceramic resonators, and those based on electrical phase-shift circuits such
as RC (resistor, capacitor) oscillators. Crystal and ceramic resonator-based oscillators (mechanical) typically
provide very high initial accuracy and a moderately low temperature coefficient.