Aw: IR-blasting 455 kHz with the new upstream kernel modules gpio-ir-tx and pwm-ir-tx

> Gesendet: Mittwoch, 29. Mai 2019 um 15:51 Uhr
> Von: [email protected]
> An: [email protected]
> Betreff: IR-blasting 455 kHz with the new upstream kernel modules gpio-ir-tx and pwm-ir-tx
>
> Dear colleagues
>
> My appliance (a heater) stopped responding reliably to sent IR signals after upgrading the Raspberry Pi 3 to raspbian 4.19.42. I tried both new kernel modules: gpio-ir-tx and pwm-ir-tx (new kernel modules from upstream for software and hardware Pulse Width Modulation PWM). Very occasionally, maybe once in a hundred, the heater picks the IR signal up. Prior to the upgrade, the system worked nicely; as the IR signal has a high carrier frequency (455 kHz) I had used a lirc-rpi module that I had modified for hardware PWM. I measured the signal at the GPIO pin with a picoscope and noted that the carrier frequency was a bit too high when using pwm-ir-tx (around 475 - 480 kHz) and much too low when using gpio-ir-tx.
>
> Could this be a reason for my IR signal to fail? Does anyone have experience with IR blasting at a high carrier frequency (455 kHz) using gpio-ir-tx or pwm-ir-tx?
>
> Thanks for sharing any experience that you may have.
>
> Andreas

Dear colleagues

Investigating the above 455 kHz issue further:
- for testing purposes: lirc and the pwm-ir-tx module reliably blasts to a DVD player using the default carrier frequency (38 kHz).
- a hardcoded c program using pigpio (thus avoiding all of lirc and the pwm-ir-tx module) works nicely at 455 kHz (accuracy also confirmed using picoscope).

I conclude that indeed pwm-ir-tx or its dependencies are not accurate enough for 455 kHz blasting, at least not for my heater (other appliances might be less picky). I will let the author of pwm-ir-tx know.

Andreas