DIY Remote
Control Tester
Do you have problems with your infrared
remote controls? Are their batteries dead or is
it just that some of the buttons are not working?
These and other questions involving remote controls can be readily answered with this handy
tester.
By LEO SIMPSON
Everyone loves their remote controls, don’t they? Whether they are
used to mute those irritating adverts
on TV or to fast-forward through
adverts on taped programs, they are
a real boon. And of course, they are
used on a multitude of other appliances these days so we are really lost
and frustrated when they don’t work.
It is at these times that remote
controls are instantly con
v erted
from items of utmost convenience
to items of extreme frustration. How
do you test them? You can’t see the
infrared beam that they are supposed
to emit so you don’t know if they are
functioning or not. Then again, they
might be functioning as far as some of
the buttons are concerned and others
might be dead. How do you find out?
On TV sets and other appliances
which have an “acknowledge” LED,
it is easy. Each time you press a
button on the TV’s remote control,
the “acknowledge” LED flashes and
you are instantly assured that all is
well. But the “acknowledge” LED
most likely doesn’t work when other
remote controls are pointed at it, so
there’s no help there. Some remotes
also have a telltale red LED and thus
they provide a good indication that
they are working; most don’t.
If you have a camcorder or video
camera you can generally use it to
check whether your remote is working. Just point it directly at the camera
and you will see the telltale flashes
in the viewfinder or monitor while a
button is pressed. How so? Because
most video cameras will respond to
infrared light.
But while that is handy to know,
it is not the most convenient setup if
you are plagued with a pesky remote
control that just does not want to
behave and do what it’s supposed to.
These thoughts were prompted by
my recent bout of wrestling with a
cantankerous remote control. It had
been becoming increasingly unrelia-
Silicon Chip’s Electronics TestBench 19
Fig.1: the circuit is based on an
infrared detector module which
drives the LED directly.
ble over a period of a few months. The
various users in the family responded
by slapping it, pressing its buttons
more fiercely and ultimately (shame)
by saying unseemly words to it. None
of these seemed to work as a cure.
Coincidentally, the remote control
tester to be described arrived in the
SILICON CHIP offices and I pounced on
it. The idea is simple. It has a membrane key on the small case. You press
it and then simultaneously press a
button on your suspect remote. If it
is working a LED on the remote tester
flashes brightly, in time with the data
modulated onto the infrared carrier.
This is far more convenient than
aiming the suspect remote at your TV.
The circuit of the remote control
tester is shown in Fig.1. It consists
simply of a 9V battery, a pushbutton
switch, a LED and an infrared receiver
module, M1. This infrared receiver
module is contained in a compact
tinplate case which houses a tiny
PC board. This mounts an infrared
detector diode, a surface mount
preamplifier chip and number of
other surface mount components. The
module would normally be mounted
behind a window in the front panel
of a TV, VCR, CD player or whatever
and would normally drive decoder
circuitry.
In this case, we don’t need any
decoding. Instead, we want the tester
to respond when any button on any
IR remote control is pressed. That
it does and it lights the LED on
its front panel for as long as any
button on the remote handpiece
is pressed.
The module has inbuilt
current limiting so it can
drive the red LED directly,
without resistors or any
other components being
required.
Building it
The circuit of Fig.1 is so simple
that you really don’t need a PC board
to build it but one is available as part
of a kit from Oatley Electronics. The
kit comprises a surplus PC board, a
9V battery snap connector, a high
brightness red LED, the infrared receiver chip, a membrane switch and
a small plastic case measuring 123 x
36 x 23mm.
The PC board measures 60 x 30mm
and has been designed for a more
complex circuit so there are a lot of
vacant component positions. The
photos show how the PC board is
wired and how it sits in the case. Fig.2
shows the wiring layout.
Putting it together will only take
a few minutes but you do have to
be careful with the polarity of the
infrared detector, the LED and of
This is how the PC board
looks when all the parts
are installed.
course, the battery wires. The infrared
detector module straddles one end of
the PC board and lugs on the tinplate
case are soldered to adjacent copper
pads on the PC board.
The positive battery wire passes
through a hole in the PC board and
is then wired directly to pin 2 on the
module. The LED is wired directly
across pins 1 & 2 on the module as
well. The negative lead from the battery is wired to the membrane switch
and then to pin 3 on the module.
When you have the unit complete,
connect the battery and press the
membrane switch. The LED should
flash once. Then if you aim an infrared remote control at it and press
a button, the LED should flash for
as long as the buttons are pressed.
Remember though, you also need to
keep the membrane switch on the
tester pressed.
Fixing remote controls
Well, once you have an infrared
tester you will certainly be able to
work out whether your remotes are
working or not and whether some
buttons are defective. But it is entirely
another matter to fix them.
Let me tell you the story of the
remote control that started this story.
Well, the tester indicated that the
remote was indeed malfunctioning
and the TV was OK. But where was
the fault because one or two of the
20
Silicon Chip’s Electronics TestBench
The PC board
assembly sits at the
top end of the case,
with the battery
occupying the other
end. Take care to
ensure correct battery
polarity – the
negative lead goes to
the switch.
buttons would work some of the time?
The first step was to check the
batteries, two AA cells being used
in this case. They were around 1.4V
each and although not fresh out of
the carton, they certainly should have
been good enough to run the circuit.
Most remotes will run quite happily
with cells that are down to 1.2V and
some will work with a lot less.
Mind you, the batteries are often
not the problem but corrosion of the
battery terminals can be quite obvious
when you take the trouble to look.
This can be most easily cleaned off
using a Scotch-Brite or similar scouring pad. Don’t use steel wool as it is
difficult, if not impossible, to ensure
that there are no strands of it left to
cause problems later.
While there was some corrosion on
the battery terminals of this cantankerous remote, that was not the problem. It still would not work reliably.
There was nothing for it but to pull
it apart. This involved removing one
screw on the back and then prising
the case carefully apart. That revealed
a long narrow PC board with just one
surface-mount IC, the infrared LED
and the contact patterns underneath
each rubber button. There were no
other components.
Older remotes can be expected to
have quite a few components on the
board and sometimes the fault can be
a fractured component or a broken
solder connection. This happens
because remote controls are often
dropped or sat upon.
In the case of this remote the
problem turned out to be blindingly
obvious. Not only had quite a lot of
food residue worked its way inside
the case around the buttons and along
the joins in the case but the PC board
itself was wet! A sticky liquid was
held between the rubber button sheet
Fig.2: this is the wiring layout of the remote control tester. It uses a surplus
PC board which fits into a small plastic case.
and the PC board. No doubt someone
had spilt drink over it at some stage.
Drink residues, especially beer
and cola, can be surprisingly hard to
remove in this situation and since the
PC board was largely bare in this case
I decided to clean it up using kitchen
detergent, thoroughly rinsed off with
clean water. I was sorely tempted to
dunk the whole PC board into the
washing-up detergent but thought
better of it. I also cleaned the rubber
keyboard membrane but this job must
be done carefully because it easy to
inadvertently remove the resistive
coating on the back of each button. It
is this resistive coating which completes the circuit for each button and
activates the remote control.
Having carefully rinsed off all the
detergent from the PC board and
Where To Buy The Kit
The complete kit for the remote
control tester is avail
able from
Oatley Electronics for just $5.95,
not including the 9V battery. They
also have the infrared detectors
available at $2 each or 10 for $15.
Oatley Electronics’ phone number
is (02) 9584 3563; fax (02) 9584
3561.
the keyboard membrane, the drink
residue appeared to be completely
removed but it turned out not to
be the whole cure. While it worked
better when it was reassembled, it
still would occasionally refuse to respond when some of the buttons were
pressed. And even more irritating,
sometimes none of the buttons would
work! OK, I then cleaned the board
and the button membrane again, this
time using methylated spirits.
This turned out to be effective and
the remote control then worked reliably – for a whole week! At the end of
that time, the most used button just
fell out! As you might expect, some
more unseemly words were uttered.
Several times!
There is no way that the missing
button could be stuck back into place
and since it was the one used to mute
the commercials, the whole situation
was rather frustrating. But wait!
There is a solution. I will replace
the missing button with a PC mount
snap action switch. They’re available
from Jaycar, Dick Smith Electronics
and Altronics, in various colours for
a dollar or so.
Yes, I will have to ream out the
button opening in the case but I’m
going to fix this remote, come hell or
SC
high water!
Silicon Chip’s Electronics TestBench 21
