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IR Link(BC337)

2017-07-02 03:34  
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This article describes the IR Link (BC337). 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: BC337. 


This is a battery powered IR Link which may be used in more
than one room. The standby current is extremely low – giving a
good battery life; and by shutting down in the presence of
extraneous IR radiation it copes with the problem of excessive
output current.

irlink IR Link

This circuit is not powered directly from the battery. When a
remote control signal is received, the energy stored in C2 drives
the emitter diode. At the same time, Q1 switches on briefly to
allow the battery to recharge C2. The green LED shows that the
circuit is transmitting; and the yellow LED confirms that C2
has been topped-up.

There is unwanted IR radiation in both daylight and tungsten
lighting. To minimize its effect use an opaque housing and do not
make the opening too large. (Try a horizontal slot measuring 2
cm X 1.5 cm.) Shade the receiver diodes by mounting them
side-by-side a few centimetres deep, inside the case. The depth
of shading required will depend on the lighting conditions.
(Try 5 cm to start with). To reduce the effects of visible
light, use receiver diodes with a built-in daylight filter (
Maplin CY91Y). Or cover the opening using a small piece of dark
transparent plastic. Part of the display panel from a scrap VCR
is ideal. Position the unit out of direct light and avoid
reflective surfaces. If all else fails, adjust VR1 to reduce
sensitivity. What you are aiming for is to ensure that in
standby mode Q2 remains switched off so that C2 retains its
charge. If unwanted radiation does reach the receiver it will not
result in a large output current. C2 simply discharges and the
circuit shuts down. When the source of the unwanted radiation is
removed the unit may be reset by interrupting the power supply
for a few seconds or by pushing the (optional) reset button. If
you do neither then it will reset itself after about an
hour when C2 has recharged through R7. With tw1o receiver diodes
wired in parallel, the operating range is up to about 1 meter.
The exact distance depends on the remote you are using and on the
position of VR1 (start by setting it about halfway). Correctly
focused, a plastic lens from a small magnifying glass will extend
the distance.

I used the high gain version of the BC337 because that was
what I had available. However, the only transistor whose gain is
likely to be important is the BC547C. For the infrared emitter I
used a TIL38 (Maplin YH70M) at the end of 12 meters of alarm
cable. However, the diode from a scrap remote control should be
worth trying also. tw1o diodes wired in series will give
improved output performance.

The circuit was designed with a small 9-volt alkaline battery
in mind (PP3, MN1604, 6LR61) but the prototype worked well at 6-volts using four AA batteries. The standby current was too small to measure reliably. An earphone socket makes the unit portable; so it can be used in more than one room. If you can obtain the style of socket in the diagram (Maplin HF82D), its normally closed switch can be converted to a normally open switch by releasing the inner contact as shown. This means that it will act as an on/off switch when you unplug the lead; and because it allows you to interrupt the power supply, there is no need for a reset button.

Circuit Layout:
irlink lay IR Link