Why do some TSOP1738 have a metal cross over their optical window while some do not have this cover?

Does not it obscure the view and shorten the range of the sensor? Does it have some positive effects?

Compare these two:

With metal housing and metal cross over the window Schematic without a metal housing


1 Answer 1


It is a shielding against EMI or RFI interference,

According to this article

TSOP module has an inbuilt control circuit for amplifying the coded pulses from the IR transmitter. A signal is generated when PIN photodiode receives the signals. This input signal is received by an automatic gain control (AGC). For a range of inputs, the output is fed back to AGC in order to adjust the gain to a suitable level. The signal from AGC is passed to a band pass filter to filter undesired frequencies. After this, the signal goes to a demodulator and this demodulated output drives an npn transistor. The collector output of the transistor is obtained at pin 3 of TSOP module.

Members of TSOP17xx series are sensitive to different centre frequencies of the IR spectrum.

so to avoid EMI/RFI, some of this module have the shielding, build over it

  • \$\begingroup\$ OK, this is why, there is the cover at all, but does or doesnot it interfere with efficiency of the input, when part of the input window is covered by the metal cross? If there is not much noise around, will I get better sensitivity without the shielding at all, or does not it matter for some reason? \$\endgroup\$
    – gilhad
    Feb 15, 2017 at 8:59
  • \$\begingroup\$ yes, the distance range might be lower for shielded \$\endgroup\$
    – Raj
    Feb 15, 2017 at 10:00

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