433 RF Filter

this is an rf receiver prefilter for the raspberry build with an attiny45. it prefilters the received signal to reduce the load for the raspberry that can i.e. run pilight (http://www.pilight.org). you be warned: this could potentionally damage your raspberry pi and also other hardware. i take no responsability for anny damages! try at your own risk!

1. Install avrgcc:

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sudo apt-get install gcc-avr avr-libc

2. Install modified avrdude:

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wget http://project-downloads.drogon.net/files/avrdude_5.10-4_armhf.deb
wget http://project-downloads.drogon.net/files/avrdude-doc_5.10-4_all.deb
sudo dpkg -i avrdude_5.10-4_armhf.deb
sudo dpkg -i avrdude-doc_5.10-4_all.deb

3. Calculate the MIN_PULSELENGTH and MAX_PULSELENGTH values

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MIN_PULSELENGTH =  ( shortest expected pulse - 10% ) / 10
MAX_PULSELENGTH =  ( longest expected pulse + 10% ) / 10

the shortest expected pulse is the minimal base pulse-width of all your protocols
the longest expected pulse is the maximal base pulse-width of all your protocols multiplied by 34

4. Compile and program attiny:

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make all

Additional info:

###Calculate fuses: http://www.engbedded.com/fusecalc/

###Pinout:

the first schematic protects your raspberry a little bit more, if you think it's needed use this one, i use the second one without resistors. if you want you can even power the attiny with 3.3V, it works, but i think the timing is less accurate.

Name	Raspberry Pi V2	Attiny45	433 Receiver
MOSI	19	5	-
MISO	21	6	-
SCK	23	7	-
RESET	24	1	-
PI_IN	see pilight cfg	3	-
REC_OUT	-	2	DATA_OUT

to change the pins create an .avrduderc file in your home directory containing (the numbering is wiringpi numbering!):

programmer
	id    = "gpio";
	desc  = "Use sysfs interface to bitbang GPIO lines";
	type  = gpio;
	reset = 8;
	sck   = 11;
	mosi  = 10;
	miso  = 9;
;