This circuit confuses
the infra-red receiver in a TV. It produces a constant signal that
interferes with the signal from a remote control and prevents the TV
detecting a channel-change or any other command. This allows you to
watch your own program without anyone changing the channel !! The
circuit is adjusted to produce a 38kHz signal. The IR diode is called an
Infra-red transmitting Diode or IR emitter diode to distinguish it from
a receiving diode, called an IR receiver or IR receiving diode. (A
Photo diode is a receiving diode).
There are so many IR emitters that we cannot put a generic number on the
circuit to represent the type of diode. Some types include: CY85G,
LD271, CQY37N (45¢), INF3850, INF3880, INF3940 (30¢). The current
through the IR LED is limited to 100mA by the
inclusion of the two 1N4148 diodes, as these form a constant-current
arrangement when combined with the transistor and 5R6 resistor.