TSOP4138 false triggering ???

[andybarrett1]

Hi and thanks for reading

I have interfaced a Vishay TSOP4138 IR receiver with a Microchip PIC 16f648 all is good and works well.

But all I am interested in is the first falling edge on the output of the 4138 when it sees the presence of a 38Khz source.

*** I suspect I am getting false noise and this is triggering my Pic ***

*Circuit is a per datasheet*

Looking at the  datasheet the TSOP4138 does have a pullup (25k) but what I am wondering is if I put a harder pull up (22k maybe) in parallel  then  a 0.1uf cap to ground from the OP pin to the PIC.

Would that act as a hardware  filter.....

Advice and help welcome thank you again for reading

BR
Andy

[Buriedcode]

These devices are very sensitive to noise on the power supply, as well as EMI.  I recently used a similar device and ended up with 100 ohm resistor with a 47uF cap as a LPF for the Vsupply.  I believe the application circuit in the datasheet also has this filter (but with no part values).   A good start would be a 47ohm resistor with a 10uF cap.

With that said, it will still probably get false triggers on the output, and your software should be able to cope with these.  When a remote is sending a signal the AGC kicks in and reduces the gain, so you won't get false spikes in the middle of a transmission, only when its idle.  Your software should be able to distinguish between a valid signal (NEC, sony, RC-5) and false triggers.