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Infrared gate for door(RES2)

2016-08-12 15:41  
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This article describes the Infrared gate for door (RES2). The content is very simple, very practical. The components of the article can help you understand better grasp this principle. For example, in this part of the principle, you can go to find and purchase the components: RES2. 


This is an infrared gate with tw1o sensors planned to use in
the wall in the way behind a door. It can be applied in a toilet
to keep track of that someone is inside exceeding a certain
amount of time. After that time elapsed, the circuit triggers the
digital output which can turn on a ventilator. The time
period the output is turned on can be separately controlled by a
second timer.

infragate5 Infrared gate for door

If you plan to build this circuit, beware that you may have
lots of difficulties though the schematic may seem simple. The
construction of the circuit requires some amount of equipment
like an oscilloscope and a DVM, too. Without them, the device
will do weird things you wouldn`t expect, and even if it is
correctly put together, you must adjust it with care both
mechanically in its final place and electronically with the help
of an oscilloscope. Only if you want to span about less than
20-30 inches with the infra diodes can forget about this
calibration. Alternatively you can take ideas from this


The device consists of several parts, the most critical one is
the panel with the infra LEDs. I tried to use several receiver
transistors, but best result was given by infra receiver diodes
used in TV remote control receivers. The receiver diodes must be
properly shielded from the transmitter LED(s) otherwise
the infra light will surely drive the receiver with a large
enough signal. These photodiodes should only see infrared light
coming from the mirror. The tw1o very sensitive receiver parts
should also be isolated from the transmitter electrically or the
TX signal will get across the wires to the RX lines, which
results the same effect as weak optical shielding. Use metal
shielding around the receiver amplifiers where possible. The
infrared transmitter LEDs should be close in wavelength to the
max. sensitivity band of the receivers. You can experiment with
using more LEDs and more current testing several resistor values,
but don`t exceed the 500 mA current limit flowing on the diodes
or they will burn out. Do not shield the transmitters, allow the
maximum amount of infra light to reach the mirror to extend the
possible range.

infragate1 Infrared gate for door

infragate4 Infrared gate for door

To start testing the infra LED panel, you wil need the
infragate amplifier panel and the small transmiter driver. The TX
driver will generate the digital signal for the LED driver on
the LED panel. The digital signal is 1:10 on/off to achive good
performance with lower power dissipation on the LEDs. Connect
GND, VCC planes and LEFT, RIGHT wires of the LED panel with the
amplifier panel, and drive the TX line from the TX driver.
Now you are able to start testing and calibrating the analogue
part of the circuit. If everything is ok, holding a mirror in
front of the LED panel will reflect enough signal to overdrive
the amplifier and you can check the output on the OPA 1, 7
pins with an oscilloscope. Taking the mirror farther on will
result a weakening signal on the amplifier output. Set the
orientation of the diodes to be able to get the maximum signal
amplitude on the oscilloscope screen. This is the heaviest part
of the work, don`t deal too much with it until the complete
circuit is not built. Just adjust a static state of the
construction to give the maximum signal amplitude on the output
when nothing is betw1een the diodes and the mirror and give a
small noise only when the line of sight is covered. If you are
ready with it, you can adjust the schmitt triggers built of
the other tw1o OPA parts to generate TTL pulses when the analog
signal is at its maximum and stay on the same DC level when the
received signal is missing.

infragate2 Infrared gate for door

It is also important to protect the receiver diodes from
direct light as natural light will weaken the sensitivity of the
diodes, and lamps will transform the 50/60 Hz modulation present
in the line power. Small noise is not problem, but the received
signal from the TX generator should be stronger to be able to
detect it. After the ST adjustments, connect LEDs to the 74123`s
TTL outputs through proper value resistors. The 74123 here
is used as a demodulator. If there is a periodic signal change
on the input, the output will be high, while if there is no
activity on the input for a given period of time, the output
falls low. When you cover the line of sight of one receiver
diode, the corresponding LED turns off. There should not be any
flickering in the turning on/off, the output should immediately
respond to the change without blinking.

infragate3 Infrared gate for door

If still everything is correctly working at this point, the
remaining digital circuit is the easy part of the work. The
outputs of the previous circuit (LEFT, RIGHT) directly connect to
the remaining part. The RS memory built from tw1o NAND gates
remembers the way of the last movement direction, so if someone
is in or not. If you experience problems, connect another LED to
pin 10 of the RS and check if this part does what it should. If
there was any activity in the past minutes, the first timer
is running, but it can only trigger the second timer part, if
someone is still inside. The diode from the second timer output
prevents resetting itself before the timing period is over in
case of another movement. For a 1 minute timing (first timer)
R=470k C=100u can be used, the second part would use R=1.5M
C=470u for about a 15 minute timing (t=1.1RC). The output of the
second timer (pin 9) can drive a relay activating the