How to IR LED as half-duplex transceiver or just receiver?
An infra-red LED can detect the raw infra-red signal from a remote. An oscilloscope can view the voltage across the LED (diode). A standard oscilloscope appears as a 1MEGohm resistance, in parallel with some capacitance (perhaps 25pf). The diode itself adds some capacitance as well.
 If you use a 1X oscilloscope probe, its additional capacitance will cause pulse distortion, so that diode voltage is not representative of the infra-red signal. You must sacrifice sensitivity by loading the diode with additional resistance. A loading resistor made too large slows response time for short light pulses:







simulate this circuit &ndash; Schematic created using CircuitLab
 You can improve sensitivity by using a larger-value loading resistor, with no oscilloscope cable (diode and resistor mounted right at the 'scope input jack).
In any case, the IR remote will have to butt-up very close to the LED sensor...this is far less sensitive than the infra-red receiver chip, some of which can sense a signal from many meters away.



An Infra-red LED can be used as a photodetector in an opamp circuit. It is still not tremendously sensitive, but is fast enough to detect pulses from nearly any remote source butted-up to the sensor LED:







simulate this circuit