Use this circuit to test if the light source coming from your 40khz IR emitter is actually giving out the best frequency. The schematic says to apply a GP1U5X ir module, however probably any 40khz detector module will work.Part list
R1 270 ohm resistor
L1 Visible LED
S1 On/Off Switch
IR Module Sharp GP1U5X IR Detect Module (or compatible)
L1 Visible LED
S1 On/Off Switch
IR Module Sharp GP1U5X IR Detect Module (or compatible)