4 ms·

Would be interesting to get a better understanding of how it worked. I’m assuming there was a motion sensor upstairs, though I don’t understand why it would sen

Would be interesting to get a better understanding of how it worked. I’m assuming there was a motion sensor upstairs, though I don’t understand why it would send a constant signal.

sokoloff 7y ago
There's a good chance the relevant code was running inside loop() in an Arduino sketch and "whohoo; it works!" represented the end of development on the project.
- SmellyGeekBoy 7y ago
  Like all the best projects.
- amingilani 7y ago
  I'm assuming he also didn't account for harmonics. It'd be interesting to see how dirty his transmissions made the spectrum.
  - sokoloff 7y ago
    Given that he took out 315MHz in a pretty wide area, I'm wagering he was using a specific 315MHz module and was just transmitting a near-constant signal. (A duty cycle issue rather than a harmonics issue.) Something like this: https://www.aliexpress.com/item/NEW315mhz-rf-Transmitter-and-Receiver-superheterodyne-UHF-ASK-remote-control-Module-Kit-small-size-low-power/32665290214.html https://www.aliexpress.com/item/NEW315mhz-rf-Transmitter-and...
    - riskable 7y ago
      Also don't rule out an incredibly poorly made 315Mhz transmitter. Chinese companies will see lots of bad reviews on their 315Mhz breakout board like, "Terrible product! Only works from within like 3 feet from the transmitter." So management gets mad at the engineer (who likely has no formal training or knowledge of FCC regulations) and says, "fix it!" "OK OK I'll just crank up the power!" Version 1.1 of the board is released on AliExpress a week later ("New version of board. We fixed weak signal!"). End users start getting the new board and like magic they can pick up a signal from like a mile away!
      - Cyph0n 7y ago
        Then the FCC comes knocking?
        colejohnson66 7y ago
        FCC can’t really do anything about a Chinese person selling from China
        azhenley 7y ago
        They can if someone is importing it.
        ajuc 7y ago
        Most hobbyst (at least where I live) order directly from China on ebay or aliexpress. It's cheapest this way.
        amingilani 7y ago
        That's what I do it almost all my equipment (not US, though)
        Freak_NL 7y ago
        Customs services worldwide probably won't even come close to inspecting even 1% of that unending stream of tiny plastic envelopes containing some sort of electronics heading for thousands of local hobbyists. It's a logistical impossibility.
        ajuc 7y ago
        They could blacklist everything and only pass-through stuff sent by trusted exporters I guess. Check 1% of the packages, if some exporter lied revoke his trusted status. But I highly doubt they will do it :)
        morpheuskafka 7y ago
- cptskippy 7y ago
  Why do you assume there was a microprocessor involved at all? Most PIR sensors come as modules that operate either with a normally open or normally closed trigger pin and a couple of pots for adjusting sensitivity and trigger duration. It would be easy to build a transmitter to blast out a constant high pulse and then just cut it off using a transistor or mosfet hooked up to the trigger on the PIR. Simple circuit with no microprocessor or coding required.
jjoonathan 7y ago
This is probably how it worked: https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-.. https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-.... and how it also had unintended consequences. Note how many comments there are from people who don't seem to have understood the disclaimer. I'd bet our rogue dongle-jammer was in much the same boat :)
- sigmar 7y ago
  You're probably right that they used a guide like that. It seems irresponsible to publish that blog post. 99% of Pi tinkerers will read that disclaimer in the third paragraph and either not understand that life critical devices _do_ can be interfered with or think their use-case is special/low-powered and won't do any harm.
  - riskable 7y ago
    The irresponsible part is that he says you "must use a filter" if you attach an antenna but does not describe what that would entail. There's not even a link anywhere that would describe how to make a filter or even what he's talking about ("I have a filter... There's no bad power going into this thing!") When you, "make something dangerous easy" you have a responsibility to be very specific in how to use your invention safely. Otherwise disaster seems inevitable.
    - maxerickson 7y ago
      You can buy razor blades almost everywhere for like a dollar. (Reviewing this comment later I see it can be read in sort of a nasty way; my meaning was that we don't really assign blame to providers of dangerous tools, the low price of razor blades reflects this)
- argd678 7y ago
  I see, so it was constantly broadcasting and then he’d encode some message in the signal to indicate if someone was up stairs, instead of only broadcasting when there was a message to send. That certainly would explain it.

Would be interesting to get a better understanding of how it worked. I’m assuming there was a motion sensor upstairs, though I don’t understand why it would send a constant signal.

sokoloff 7y ago

There's a good chance the relevant code was running inside loop() in an Arduino sketch and "whohoo; it works!" represented the end of development on the project.

SmellyGeekBoy 7y ago
Like all the best projects.
amingilani 7y ago
I'm assuming he also didn't account for harmonics. It'd be interesting to see how dirty his transmissions made the spectrum.
- sokoloff 7y ago
  Given that he took out 315MHz in a pretty wide area, I'm wagering he was using a specific 315MHz module and was just transmitting a near-constant signal. (A duty cycle issue rather than a harmonics issue.) Something like this: https://www.aliexpress.com/item/NEW315mhz-rf-Transmitter-and-Receiver-superheterodyne-UHF-ASK-remote-control-Module-Kit-small-size-low-power/32665290214.html https://www.aliexpress.com/item/NEW315mhz-rf-Transmitter-and...
  - riskable 7y ago
    Also don't rule out an incredibly poorly made 315Mhz transmitter. Chinese companies will see lots of bad reviews on their 315Mhz breakout board like, "Terrible product! Only works from within like 3 feet from the transmitter." So management gets mad at the engineer (who likely has no formal training or knowledge of FCC regulations) and says, "fix it!" "OK OK I'll just crank up the power!" Version 1.1 of the board is released on AliExpress a week later ("New version of board. We fixed weak signal!"). End users start getting the new board and like magic they can pick up a signal from like a mile away!
    - Cyph0n 7y ago
      Then the FCC comes knocking?
      - colejohnson66 7y ago
        FCC can’t really do anything about a Chinese person selling from China
        azhenley 7y ago
        They can if someone is importing it.
        ajuc 7y ago
        Most hobbyst (at least where I live) order directly from China on ebay or aliexpress. It's cheapest this way.
        amingilani 7y ago
        That's what I do it almost all my equipment (not US, though)
        Freak_NL 7y ago
        Customs services worldwide probably won't even come close to inspecting even 1% of that unending stream of tiny plastic envelopes containing some sort of electronics heading for thousands of local hobbyists. It's a logistical impossibility.
        ajuc 7y ago
        They could blacklist everything and only pass-through stuff sent by trusted exporters I guess. Check 1% of the packages, if some exporter lied revoke his trusted status. But I highly doubt they will do it :)
        morpheuskafka 7y ago
cptskippy 7y ago
Why do you assume there was a microprocessor involved at all? Most PIR sensors come as modules that operate either with a normally open or normally closed trigger pin and a couple of pots for adjusting sensitivity and trigger duration. It would be easy to build a transmitter to blast out a constant high pulse and then just cut it off using a transistor or mosfet hooked up to the trigger on the PIR. Simple circuit with no microprocessor or coding required.

jjoonathan 7y ago

This is probably how it worked: https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-.. https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-.... and how it also had unintended consequences. Note how many comments there are from people who don't seem to have understood the disclaimer. I'd bet our rogue dongle-jammer was in much the same boat :)

sigmar 7y ago
You're probably right that they used a guide like that. It seems irresponsible to publish that blog post. 99% of Pi tinkerers will read that disclaimer in the third paragraph and either not understand that life critical devices _do_ can be interfered with or think their use-case is special/low-powered and won't do any harm.
- riskable 7y ago
  The irresponsible part is that he says you "must use a filter" if you attach an antenna but does not describe what that would entail. There's not even a link anywhere that would describe how to make a filter or even what he's talking about ("I have a filter... There's no bad power going into this thing!") When you, "make something dangerous easy" you have a responsibility to be very specific in how to use your invention safely. Otherwise disaster seems inevitable.
  - maxerickson 7y ago
    You can buy razor blades almost everywhere for like a dollar. (Reviewing this comment later I see it can be read in sort of a nasty way; my meaning was that we don't really assign blame to providers of dangerous tools, the low price of razor blades reflects this)
argd678 7y ago
I see, so it was constantly broadcasting and then he’d encode some message in the signal to indicate if someone was up stairs, instead of only broadcasting when there was a message to send. That certainly would explain it.