[SOLVED] IR receptor doesn't work when MAX232 is connected to VCC

[AveztruZ]

I've got a really strange issue... I have a PIC18F4520 using MAX232 to communicate with my PC, everything was fine. Then I bought a IR receptor and tested it alone with osciloscope, it was also working as expected, but when I connected the IR receptor to the same GND and VCC as the PIC and MAX232 it stopped working.
I removed the MAX232 from the circuit and the IR receptor worked. If I connect again the IR receptor will stop.

I dont wanna have another power supply for IR receptor once it will be a portable device.

Does anyone know what is going on?

 

[andre_luis]

Would be helpful if you can provide few more details, particularly concerning to the IR receptor interface.



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[AveztruZ]

Where I bought it says that the model is TSDLZ0KSM903L, but I didnt find anything related to this code. In the back it is written 68v3 ka25, and I also didnt find anything.
It looks similar to this one:
http://i01.i.aliimg.com/photo/v2/511243805/infrared_remoto_control_receiver_module_DQIR_38343E8.jpg

I hope it helps.

 

[FvM]

Did you verify that the supply voltage is still present and has correct level? Also the sensor output shouldn't be shorted by other circuit parts.

MAX232 is generating nasty current spikes on the supply voltage. You should have bypassing capacitors between VCC and GND near the MAX232 and remote control receiver. It may be helpful to have a RC power supply filter (e.g. 100 ohm/1µF) for the sensor supply.

 

[ard]

How are you powering the IR receiver? Directly from the Vcc? Thats a strict no-no.

Insert a 330 ohm resistor between Vcc and the module's power pin. Then add a 10uf capacitor across the IR module's power and ground pins. That should resolve the issue.

 

[AveztruZ]

Thank you guys... It is working!

I was using a poor osciloscope and didnt see that spikes, with a better one I could see it and I replace the capacitor close to MAX232 with a higher capacitance, and also did this filter that ard said!

there is a doubt left... why 330 ohms and 10uf? could someone explain me!

 

[FvM]

Most datasheets are suggesting 100 ohm series resistor and several µF capacitor. Design criterion is sufficient suppression of 38 kHz noise.