IR TRANSMITTER, RECIEVER
Infrared
is a energy radiation with a frequency below our eyes sensitivity, so we cannot
see it. Even that we cannot "see" sound frequencies, we know that it
exist, we can listen them .
IR TRANSMITTER
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| IR Transmitter-receive |
IR SECTION
INFRARED(IR)
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Fig of Infra ed(IR)
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INFRARED IN ELECTRONICS
Infra-Red is interesting, because it is
easily generated and doesn't suffer electromagnetic interference, so it is
nicely used to communication and control, but it is not perfect, some other
light emissions could contains infrared as well, and that can interfere in this
communication. The sun is an example, since it emits a wide spectrum or
radiation.
IR GENERATION
To
generate a 36 KHz pulsating infrared is quite easy, more difficult is to
receive and identify this frequency. This is why some companies produce
infrared receives, that contains the filters, decoding circuits and the output
shaper, that delivers a square wave, meaning the existence or not of the 36kHz
incoming pulsating infrared.
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Fig IR Generation
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The IR LED emitting infrared light is put on in the transmitting unit. To generate IR signal, 555 IC based astable multivibrator is used. Infrared LED is driven through transistor BC 548.
IC 555 is used to construct an astable multivibrator which has two quasi-stable states. It generates a square wave of frequency 38 kHz and amplitude 5Volts. It is required to switch ‘ON’ the IR LED. The IR transmitter circuit is as shown below.
IC 555 is used to construct an astable multivibrator which has two quasi-stable states. It generates a square wave of frequency 38 kHz and amplitude 5Volts. It is required to switch ‘ON’ the IR LED. The IR transmitter circuit is as shown below.
Fig IR Transmitter
555 TIMERS
The 555
is an integrated circuit (chip) implementing a variety of timer and
multivibrator applications. It was designed in 1970 and introduced in 1971 by Sign
tics (later acquired by Philips). The original name was the SE555/NE555 and was called "The IC Time
Machine". It is still in wide use, thanks to its ease of use, low price
and good stability. As of 2003, 1 billion units are manufactured every year.
The 555 timer is one of the most popular and
versatile integrated circuits ever produced. It includes 23 transistors, 2
diodes and 16 resistors on a silicon chip installed in an 8-pin mini
dual-in-line package (DIP-8). The 556 is a 14-pin DIP that combines two 555s on
a single chip.
Pin Functions - 8 pin
package
Output (Pin 3)
Control (Pin 5)
Threshold (Pin 6)
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Fig 555 Timers
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Pin Functions - 8 pin
package
Ground
(Pin 1)
This
pin is connected directly to ground.
Trigger
(Pin 2)
This
pin is the input to the lower comparator and is used to set the latch, which in
turn causes the output to go high.
Output (Pin 3)
Output
high is about 1.7V less than supply. Output high is capable of sourcing up to
200mA while output low is capable of sinking up to 200mA.
Reset
(Pin 4)
This is
used to reset the latch and return the output to a low state. The reset is an
overriding function. When not used connect to V+.
Control (Pin 5)
Allows access to the 2/3V+
voltage divider point when the 555 timer is used in voltage control mode. When
not used connect to ground through a 0.01 uF capacitor.
Threshold (Pin 6)
This is an input to the upper
comparator.
Discharge
(Pin 7)
This is
the open collector to Q14.
V+ (Pin
8)
This
connects to Vcc and the Philips data book states the ICM7555 CMOS version
operates 3V - 16V DC while the NE555 version is 3V - 16V DC.
The 555 has three operating modes:
- Monostable
mode: in this mode, the 555 functions as a "one-shot".
Applications include timers, missing pulse detection, bounce free
switches, touch switches, Frequency Divider, Capacitance Measurement,
Pulse Width Modulation (PWM) etc
- Astable
mode: Free Running mode: the 555 can operate as an oscillator. Uses
include LED and lamp flashers, pulse generation, logic clocks, tone
generation, security alarms, pulse position modulation, etc.
- Bistable
mode: The 555 can operate as a flip-flop, if the DIS pin is not connected
and no capacitor is used. Uses include bounce free latched switches, etc.
IR RECIEVER
Description
The TSOP17.. – Series are
miniaturized receivers for infrared remote control systems. PIN diode and
preamplifier are assembled on lead frame, the epoxy package is designed as IR
filter.
The demodulated output signal
can directly be decoded by a microprocessor. TSOP17.. is the standard IR remote
control receiver series, supporting all major transmission codes.
Features
- Photo detector and preamplifier in one
package
- Internal filter for PCM frequency
- Improved shielding against electrical
field disturbance
- TTL
and CMOS compatibility
- Output active low
- Low
power consumption
- High immunity against ambient light
- Continuous data transmission possible (up
to 2400 bps)
- Suitable burst length .10 cycles/burst
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Fig Block Diagram
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