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Comment by erjiang | Hacker News Reader

If anyone has a Raspberry Pi and is interested, check out rpitx[0]. It bit-bangs a GPIO pin to transmit arbitrary radio, turning your Pi into a messy SDR transmitter. By connecting a wire to the GPIO pin you can transmit for tens of meters.

I attached a low-pass filter to the GPIO pin and was able to control my ceiling fan with my Raspberry Pi.

[0] https://github.com/F5OEO/rpitx

Edit: This generates square waves which have harmonics. You will transmit signals on unintended frequencies if you don't use a filter.

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"So the FCC won't let me be...."

The FCC doesn't really care unless someone complains about interference. Given that the range of this is so low, the signal is unlikely to even reach your neighbors much less interfere with anything.

Depends on who's the complainer! If it's an enterprise-level business, the FCC is going to storm in. If it's an individual, it's probably going to have to be whoever the mayor of your town points their finger at when they get a call to their hotline. My technician father was on the end of this once - he helped install a wireless water pressure sensor for the water utility and was called 200 miles back to the customer check out why someone was complaining about TV interference. With some radio test equipment, he determined it was... the complainer's electric blanket interfering with their TV!

Yeah, I really wouldn't recommend doing this in a city. Even though the output power probably isn't much, there will be so many spurious emissions and harmonics that you don't know who you'll interfere with.

Nice reference...Now the song wont leave my head

RPITX is very poor at AM (3 power levels), but it is still awesome. Digging obscure forums I found it could do LSB and USB, which was an interesting find even for the creator.

If you like cheap hack sdrs, you might also want to check https://osmocom.org/projects/osmo-fl2k/wiki -- it is a repourposed HDMI sdr.

I just found this a few weeks ago as I started to look at a way to hack a cheap set of wireless controlled outlets for my Christmas lights. I needed a SDR to record the signal from the remote, but now I have my lights controlled by a cron job on a Raspberry Pi that is on my desk.

Excellent! Have you been able to transmit anything at all without connecting a wire over the outputs?

Or are there are popular configurations where people have something plugged in and then unwitting be open to an exfiltration attack?

Range without an antenna is around 10-20cm. I was able to hold my RPi next to my ceiling fan and control it, but obviously that’s not very practical.

Theoretically you could exfiltrate data with it, but if you have root access to the RPi already then I don’t see why you wouldn’t just use Wi-Fi.

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