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.