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GSK-58
IR Toggle Switch
The GSK-58 is an infra-red (IR) toggle switch kit,
which should work with any button on any modern
remote control module. Push any button of your
remote control unit and the relay in our Kit will turn
on. Push any button a few seconds or hours later
and the relay will toggle off.
How It Works
All modern IR remote control devices produce a con-
tinuous coded stream of pulses at 37.9 kHz when
any button on the module is pressed. These IR
pulses are detected and decoded by a receiver (your
TV, DVD etc.) and the appropriate function activated.
In our Kit the coded stream is converted into a single
pulse and that single pulse is used to toggle a relay
on & off. The coded information is lost. Only the fact
that a button was pressed on your remote control
unit is detected. This single pulse is then used to
toggle the output of a flip-flop. A high on the /Q
output of the flip-flop turns on transistor Q3, which
in turn operates the relay and the LED. The LED
provides visual indication that the relay is operating.
Circuit Description. The Kodenshi IR receiver
module in the GSK-58 detects and decodes the 37.9
kHz input as a train of negative pulses. These
negative pulses are inverted by transistor Q1. Then
these positive pulses are converted to a single pulse
by the network R4, Dl, R5& C2. The positive pulses
on the collector of Q1 charge capacitor C2 via
resistor R4 and diode Dl. The charging lime is
approximately 12.5msec (R4 x C2). During the low
time between pulses the collector of Q1 is low and
C2 begins to discharge. However, the discharge path
is via R5 because D1 is now reverse-biased and
therefore non-conducting. The discharge time is
about 0.5 sec (R5 x C2). Since the frequency of the
received pulses is much faster than the discharge
time of the capacitor C2, the capacitor cannot fully
discharge before the next IR pulse train is received.
The charging cycle of capacitor C2 provides the
rising edge needed to clock the flip-flop.
The flip-flop (FF) is a D-type. The voltage level at the
D input is transferred to the Q output on the rising
edge of the clock pulse. Since we are using the
inverted /Q output, a low level at D will cause /Q to go
high and a high level at D will cause /Q to go low. The
output of the FF can only be changed with the next
rising edge of the clock input.
The /Q output which drives the relay is also fed to
the D input via resistor R6 & capacitor C3. This
allows the output of the FF to toggle between high
Instruction Manual
and low with every clock pulse received. With /Q
high, C3 is charged via R6. After about 1,2 seconds
(R6 x C3) the D input will rise to a digital high level.
This high
will be transferred to the output on the next clock
pulse. This will cause /Q to go low, thus discharging
C3. After 1.2 seconds the D input will go low ready
for the next clock input.
A feedback delay between the output and input is
necessary to keep the input stable while clocking the
FF. The delay time chosen (1.2 seconds in this case)
determines how quickly the relay can be toggled.
Power Supply. Any DC voltage in the range 8 to
15V can be used. This voltage is regulated to 5V by
Q2, RS and ZD1. The zener diode holds the base of
Q2 at 5.6 volts and Q2 conducts. The emitter voltage
is equal to the base voltage less the voltage dropped
across the base-emitter junction (about 0.6V). So
the output is 5V. Capacitor C5 provides filtering for
any high frequency noise. (Note that Q2, R8, ZD1 &
C5 could be replaced by a single 5V regulator IC.)
Construction
First, check that you have all the components. Check
each component against the Listing given on the
next page. In particular make sure you know which
diode is the 1N4148 (it has 4148 printed on it in tiny
numbers) and which is the 5V6 zener diode (it is
packed in a compartment of the plastic bag all by
itself.) Make sure to get the orientation of the diodes
correct. The bar on the diode is the cathode and
corresponds with the bar on the overlay printed on
the circuit board.
It is generally easiest to add and solder the lowest
height components first to the PCB - the resistors,
diodes and monocapacitors. Then add the taller
components. Pay attention to the polarization of the
electrolytic capacitors and the LED. Note that Q1 is a
BC558 while Q2 & Q3 are BC548's. As indicated on
the overlay the dimple on the IR receiver module
should be directed outwards.
Relay. We have designed the board to use a
miniature, 5 pin Goodsky Brand relay AZ-SH-112L.
The maximum contact current is 1A. This on-board
relay should be used to control an off-board relay or
switch. It should not be used to switch high currents
or high voltages directly. That is not its function. The
Common (C), Normally Connected (NC), and
Normally Open (NO) connections are taken to a 3-
pole terminal block on the right hand edge of the
board.
