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IR remote control extender (CA3140)

2015-02-28 08:38  
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This circuit is used to relay signals from an Infra Red remote
control in one room to an IR controlled appliance in another


I have seen these devices advertised in magazines, they sell
for around £40-£50 and use radio to transmit betw1een receiver
and transmitter. This version costs under £5 to make and uses a
cable connection betw1een 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:

irext IR remote control extender

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 CA31340 is available in the US from Electronix Express, part number N103140.

This article describes the IR remote control extender (CA3140). The content is very simple, very helpful. Components in this article can help you understand better understanding of this article. For example, in this article, you can go to find and buy these components:CA3140.

Circuit Advantages

The advantage of this design against similar designs is that
there are no adjustments to make or set-up procedures. However
care should be taken to avoid ambient light reaching the
photodiode. A dayligt filter type (black in colour) is
recommended. Bellwire or speaker cable may 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 tw1o 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, betw1een 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
betw1een 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


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.

ca3140c IR remote control extender


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

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 tw1o
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:

Mk1pcb IR remote control extender

A magnified view from the component side is shown below.
Unfortunately the transistor outline was reversed in the original
diagram, my thanks go to Federico Laura for correcting this
diagram :

Mk1com IR remote control extender


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