This small circuit is
ideal for checking the basic operation of an infrared remote control
unit. The circuit is based on the brilliantly simple idea of connecting a
piezo buzzer directly to an IR receiver IC. This method is almost as
simple as connecting a photodiode directly to the input of an
oscilloscope, but has the advantage that no oscilloscope is needed: the
compact unit is always ready to use and much easier to carry around than
bulky test equipment.
Operation of the remote control is indicated by the buzzer making a
chattering noise. The circuit is very sensitive and has a range of
several meters. The TSOP1738 integrated IR receiver accepts, amplifies
and demodulates the IR signal from the remote control, producing an
output with a frequency of around 700 Hz. The piezo buzzer is connected
to its output, rendering the signal audible. All the other components
are simply concerned with producing a stable 5 V power supply from the
9V PP3-(6F22) type battery.
Instead of the TSOP1738 similar devices from other manufacturers can
be used, and of course carrier frequencies other than 38 kHz can be
used. The circuit still works if there is a mismatch between the nominal
carrier frequencies of the transmitter and receiver IC, but range is
reduced. It is still, however, adequate for determining whether a remote
control is producing an IR signal or not.
Author: Malte Fischer – Copyright: Elektor Electronics Magazine