Some people might find it difficult to use the TSOP1738 or TSOP1838 (the only major difference is the pin configuration and packaging), so I am going to write a brief tutorial on how to do just that.
From left to right, when seen from the front side;
TSOP1838: Output, Ground, Vcc
TSOP1738: Ground, Vcc, Output
I will not get into the detail of generation of 38KHz using an AVR or PIC or 8051 microcontrollers. The datasheets and many websites point to the instruction of sending 6 to 70 pulses of 38KHz square wave, and then some 10 pulses of low signal. But the this format is quite dependent on the receiver and the circuit that we have set up. From what I have experienced, it worked best for me with a capacitor of about 22uF across Vcc and Ground, and a 10K pull-up at the output.
What I do, is send a burst of 38KHz SW for about 400us and let it rest for 5ms. When working on proximity sensors, or people counters, the output of receiver should be immediately checked for after sending the burst. This way, the receiver will not saturate, and work as expected.
Edit: This is what I originally intended to write most importantly, that the TSOP IR receiver actually gives low output during the time when it is absorbing 38KHz square wave. But the wave shouldn’t last longer than recommended 6 to 70 pulses because it would saturate the receiver and the output would go high again.
So to transfer data, for example, vary the number of pulses to indicate 1 and 0, and check the period in the receiving end.