Infra Red Remote Control Extender (Mark 1)
Circuit : Andy Collinson
This circuit is used to relay signals from an Infra Red remote control in one room to an IR controlled appliance
in another room.
I have seen these devices advertised in magazines, they sell for around £40-£50 and use
radio to transmit between receiver and transmitter. This version costs under £5 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:
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.
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 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
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. The opamp is configured as a current to voltage convertor,
producing an output of about 4.7 volts 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.
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.
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.
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.
This has been very kindly drafted by Domenico from Italy. First the copper side:
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 :
Mark 1A Version
The modification to the Mark 1 circuit below separtes IR handset signals from daylight and mains powered
lighting. The 22n capacitor has a high impedance at 50/60Hz and daylight but allows a modulated
signal to pass. The 2N2222 transistor is biased on under no signal, the BC337 will be fully off.
A control signal will switch off and on the 2N2222 transistor at the modulation frequency of
the control, which in turn controls the BC337. As this is a cleaner signal, the series resistor
may be increased to 100ohms.
Last revision 8 November 2004