16-05-2012, 04:18 PM
Long-Range IR Transmitter
LONGRANGEIRTRANSMITTER.PDF (Size: 207.03 KB / Downloads: 36)
Most of the IR remotes work reliably
within a range of 5 metres.
The circuit complexity
increases if you design the IR transmitter
for reliable operation over a longer
range, say, 10 metres. To double the
range from 5 metres to 10 metres, you
need to increase the transmitted power
four times.
If you wish
to realise a
highly directional
IR beam
(very narrow
beam), you can
suitably use an
EFY Lab
Long-Range IR Transmitter s.c. dwivedi
IR laser pointer as the IR signal source.
The laser pointer is readily available in
the market. However, with a very narrow
beam from the laser pointer, you
have to take extra care, lest a small jerk
to the gadget may change the beam
orientation and cause loss of contact.
Here is a simple circuit that will
give you a pretty long range. It uses
three infrared transmitting LEDs (IR1
through IR3) in series to increase the
radiated power. Further, to increase
the directivity and so also the power
density, you may assemble the IR LEDs
inside the reflector of a torch.
For increasing the circuit efficiency,
a MOSFET (BS170) has been used,
which acts as a switch and thus reduces
the power loss that would result
if a transistor were used. To avoid any
dip during its ‘on’/‘off’ operations, a
100μF reservoir capacitor C2 is used
across the battery supply. Its advantage
will be more obvious when the
IR transmitter is powered by ordinary
batteries. Capacitor C2 supplies extra
charge during ‘switching
on’ operations.
As the MOSFET exhibits
large capacitance
across gate-source terminals,
a special drive
arrangement has been
made using npn-pnp
Darlington pair of
BC547 and BC557 (as
emitter followers), to
avoid distortion of the
gate drive input. Data
(CMOS-compatible) to
be transmitted is used
for modulating the 38
kHz frequency generated
by CD4047 (IC1).
However, in the circuit
shown here, tactile
switch S1 has been
used for modulating
and transmitting the IR signal.
Assemble the circuit on a general-
purpose PCB. Use switch S2 for
power ‘on’/‘off’ control. Commercially
available IR receiver modules
(e.g., TSOP1738) could be used for
efficient reception of the transmitted
IR signals.