The TSOP 1838 is a member of IR remote control receiver series. This IR sensor module consists of a PIN diode and a preamplifier which are embedded into a single package. The output of TSOP is active low and it gives +5V in off state. When IR waves, from a source, with a center frequency of 38 kHz incident on it, its output goes low.
Lights coming from sunlight, fluorescent lamps etc. may cause disturbance to it and result in undesirable output even when the source is not transmitting IR signals. A bandpass filter, an integrator stage, and automatic gain control are used to suppress such disturbances.