Design of this IR-repeater is based on a photo detector TSMP58138 made by Vishay. This detector differs from many others of this kind by the carrier out signal. The datasheet gives a sample circuit for a repeater application. This design offers slightly modified circuit with visual feedback and an implementation in form of a RJ45 plugin.
The output of photo detector is inverted and its current not sufficient to drive an IR emitter. The inverting amplifier is implemented with a PNP transistor, such as BC212. Resistors R1 and R2 limit current flown via LEDs.
The wiring issue is solved by using spare pairs from an existing CAT5 cable. This decision also guided the implementation – the circuit is split on two parts – a front-end with detector and feedback LED, and a back-end with the inverting amplifier.
The leads of the photo detector and LED are crimped directly into the RJ45 connector. The other components are mount on a prototyping PCB.