[ripper121]

Hi all,
is it possible to do the Band Pass Filter with passive Components?
Because then there is no need to flash a µC.


With best regards
Ripper121

[curlymo]

If you can build one, please do!

[ripper121]

Which frequencys should be passed and which one not?

[curlymo]

433.92Mhz

[ripper121]

Are you sure?
Because the Atiny85 FW checks for
MIN_PULSELENGTH = ( shortest expected pulse - 10% ) / 10
MAX_PULSELENGTH = ( longest expected pulse + 10% ) / 10
and not for a freq.

---

I think you can use this.
A Saw filter when you really filter 433 with the Attiny85.

https://www.digikey.ca/product-detail/en...ND/3307725

[curlymo]

You meant the pulse frequency?

[ripper121]

You said the pass freq is 433.92Mhz.
The attiny85 (your lowpassfilter) is filtering this freq. 433.92Mhz.

When i take a look at the github of the firmware for the attiny85 it says:
MIN_PULSELENGTH = ( shortest expected pulse - 10% ) / 10
MAX_PULSELENGTH = ( longest expected pulse + 10% ) / 10

So I'm not sure if the attiny85 filter really the 433.92Mhz or anything else.

[curlymo]

The ATTiny should pass through 433.92Mhz, that what the receiver receives. The pulse lengths it should accept are between 100us and 70000us (i believe).

[wo_rasp]

No ,a 433 MHz Filter is not sufficient, as OOK modulation of a 433 MHz carrier is used and as we do not deal with sinus wave signals either you could use the 5th or 7th harmonic of a pulse duration, however due to the fact that some devices have a pulse duration of 80 mSec, others of 2mSec and the minimum is approximately 0,15 mSec you face some difficulties with a proper analog circuit design.
IMHO on a Pi2 or Pi3 it is best to operate the LPF in no filter mode as sufficient CPU power is available.

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