Infra Red Remote Control Extender
Description
This circuit is used to relay signals from an Infra Red remote control
in one room to an IR controlled appliance in another room.
Forward
I have seen these devices advertised in magazines, they sell for around Ј40-Ј50 and use radio to transmit between receiver and transmitter. This
version costs under Ј5 to make and uses a cable connection between
receiver and transmitter. For example, if you have a bedroom TV set that
is wired to the video or satellite in another room, then you can change
channels on the remote satellite receiver using this circuit. The idea
is that you take your remote control with you, aim at the IR remote
control extender which is in the same room, and this will relay the IR
signal and control the remote appliance for you. The circuit is
displayed below:
Parts List:
1 SFH2030 Photodiode
1 TIL38 IR emitting diode
1 5mm Red LED
2 4.7M 1/4W resistors
1 1k 1/4W resistor
1 2.2k 1/4W resistor
1 27ohm 1/2W resistor
1 BC337 transistor
1 CA3140 MOSFET opamp
The LPC661 opamp Radio Shack # 900-6332 can be used as a substitute for
the CA3140
Circuit Benefits
This circuit has an advantage over other similar designs in that there
is nothing to adjust or set-up. Also bellwire or speaker cable can be
used to remotely site the IR emitting diode, since this design uses low
output impedance and will not pick up noise. Some systems require
coaxial cable which is expensive and bulky. The wireless variety of
remote control extenders need two power supplies, here one is used and
being radio are inevitably EM noise pollution. A visual indication of
the unit receiving an Infra Red signal is provided by LED1. This is an
ordinary coloured LED, I used orange but any colour will do. You will
see LED1 flash at a rate of 4 - 40Hz when a remote control button is
pressed. LED0 is an Infra Red Emitter Diode, this is remotely wired in
the room with the appliance to be controlled. I used the type SFH487
which has a peak wavelength of 880nm. This is available in the UK from
Maplin Electronics, order code CY88V. Most IR remote controls operate at
slightly different wavelengths, between the range of 850 - 950nm. If you
cannot obtain the SFH487 then any IR emitter diode that has an output in
the above range should work.
About IR Remote Controls
As previously stated IR remote controls use wavelengths between 850 -
950nm. At this short wavelength, the light is invisible to the human
eye, but a domestic camcorder can actually view this portion of the
electromagnetic spectrum. Viewed with a camcorder, an IR LED appears to
change brightness. All remote controls use an encoded series of pulses,
of which there are thousands of combinations. The light output intensity
varies with each remote control, remotes working at 4.5V dc generally
will provide a stronger light output than a 3V dc control. Also, as the
photodiode in this project has a peak light response at 850nm, it will
receive a stronger signal from controls operating closer to this
wavelength. The photodiode will actually respond to IR wavelengths from
400nm to 1100nm, so all remote controls should be compatible.
Circuit Description
The receiver is built around a silicon photodiode, the SFH2030 available
from Maplin, order code CY90X. This photodiode is very sensitive and
will respond to a wide spectral range of IR frequencies. There is a
small amount of infra red in direct sunlight, so make sure that the
diode does not pick up direct sunlight. If this happens, LED1 will be
constantly lit. There is a version of the SFH2030 that has a daylight
filter built in, the SFH2030F order code CY91Y. A TIL100 will also give
good results here. A photodiode produces minute pulses of current when
exposed to infra red radiation. This current (around 1uA with the
SFH2030 and a typical IR control used at a distance of 1 meter) is
amplified by the CA3140 opamp. This is configured as a differential
amplifier and will produce an output of about 1 volt per uA of input
current. The photodiode, can be placed up to a meter or so away from the
circuit. Screened cable is not necessary, as common mode signals (noise)
will be rejected. It is essential to use a MOSFET input type here as
there is zero output offset and negligible input offset current. A 741
or LF351 can not be used in this circuit. The output from the opamp is
amplified by the BC337 operating in common emitter mode. As a MOSFET
opamp IC is used, its quiescent voltage output is zero and this
transistor and both LED's will not be lit. The 1k resistor makes sure
that the BC337 will fully saturate and at the same time limits base
current to a safe level. Operating an IR remote control and pointing at
the photodiode (SFH2030) will cause both LED's to illuminate, you will
only see the visable coloured LED (LED1) which will flicker. Remote
controls use a system of pulse code modulation, so it is essential that
the signal is not distorted by any significant amount. Direct coupling,
and a high speed switching transistor avoid this problem.
Construction
No special PCB is required, I built my prototype on a small piece of
Veroboard. The pinout for the CA3140 is shown below. Note that only the
pins labeled in the schematic are used, pins 1, 5 and 8 are not used and
left unconnected.
Alignment
There is nothing to set-up or adjust in this circuit. The only thing to
watch is that the emitting diode is pointing at the controlled device
(video, CD player, etc). I found that the beam was quite directional.
Also make sure that there is a direct line of sight involved. It will
not work if a 5 foot spider plant gets in the way, for example. I had a
usable range at 5 meters, but possibly more distance may be possible. As
a check, place a dc volt meter across the 27 ohm resistor. It should
read 0 volts, but around 2 or 3 volts when a remote control is aimed at
the photodiode.
Specifications of Prototype
Having made my prototype, I ran a few tests :-
Current consumption 2mA standby 60mA
operating ( with 12V supply)
2mA standby 85mA operating (with
15V supply)
IR receiver range < 1 meter
IR transmitter range > 5 meters
It is difficult to measure the IR transmitter range as this is dependent
upon a number of factors. The type of infra red control used and its
proximity to the receiving photodiode, the voltage supply, the
wavelength and efficiency of the IR emitter and the sensitivity of the
controlled appliance all affect overall performance.
In Use
The reception range of the IR remote control to the photodiode depends
on the strength of the remote control, but I had a working range of a
meter or so, this needs bearing in mind when placing the circuit. Its
also a good idea to wire LED1, the coloured LED near to the photodiode,
that way, you know that the unit has received a signal. The IR emitter
has a larger range, I had no problems at 5 meters but may possibly work
further distances. The emitting diodes are quite directional, so make
sure it is aimed directly at the appliance to be controlled. The IR
emitting diode is small and can be placed out of sight. I drilled a
small hole above the door frame. The emitter diode leads were insulated
and pushed through this hole, leaving an inch or so to adjust the angle
and position of the LED. From a distance, the clear plastic lens of the
diode could not be seen.
Final Comments and Fault Finding
To date this has proved to be one of the most popular circuits on my
site. Of all the email I receive about this circuit, most problems
relate to the Infra Red photo diode. You must make sure that this is
pointed away from sunlight, or use a type with daylight filter,
otherwise LED1 will be constantly lit, and LED0 will be in operation
also. This will draw excessive current and in some case overheat the
BC337. The main problem is when using a different photo diode to the
SFH2030. Any other photo diode LED should work, but you need to know its
operating wavelength range beforehand. This will generally be described
in the manufacturers data sheet or possibly described if you order from
an electronic component catalogue. With these last two points in mind,
you should be rewarded with a useful and working circuit.
PCB Template
This has been very kindly drafted by Domenico from Italy. First the
copper side:
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