4 ms·

I can often tell that I'm about to receive a text message because my poorly shielded computer speakers will start buzzing. I assume it's caused by a transmissio

by beala 9y ago

I can often tell that I'm about to receive a text message because my poorly shielded computer speakers will start buzzing. I assume it's caused by a transmission from my phone's radio inducing a current in the amplification circuit. I would guess this is what's happening with your GFI. Even though you're receiving the call, your phone is probably transmitting too (sending back the equivalent of an ACK or something). The current induced causes a difference between hot and neutral and the GFI trips. It's surprising that it can induce a strong enough current! I'm not sure what wattage cell phone radios operate at. Edit: Ah missed the detail about outgoing calls not causing it. That is very strange! Perhaps a cell phone engineer can shed some light on that!

SOLAR_FIELDS 9y ago
I’m guessing car manufacturers have caught onto this. I drove a year 2000 car whose speakers would know I was about to receive a text/call several seconds before receiving it. I don’t think I’ve been in a model later than 2008 that’s had this problem. The noise, like the AOL dialup modem beeps, are one of those things that become cemented in your brain and immediately recall themselves as soon as you think about them. I heard the short succession of beep patterns in my head as I read your comment.
- digi_owl 9y ago
  That, and possibly that newer networks work on different frequencies.
  - kalleboo 9y ago
    It's not that they use different frequencies (in a lot of places, they've actually recycled GSM frequencies for increased LTE bandwidth) but that they use a different form of modulation (than TDMA) that doesn't cause the same interference
- robocat 9y ago
  2G GSM? https://youtu.be/jBu1ILbIKZo https://youtu.be/jBu1ILbIKZo
  - digi_owl 9y ago
    Makes a guy nostalgic for beach summers when the boombox would overlay that because someone left their phone to close to it.
  - SOLAR_FIELDS 9y ago
    Yep that’s it. So it wasn’t the cars then, it was the networks being updated.
mavidser 9y ago
I remember old feature phones which had a fancy light on the back, which started blinking whenever a call was about to come through. Was a pretty nifty feature when you were expecting calls ['twas a time when I used to give "missed calls" for a callback].
- digi_owl 9y ago
  Before UMTS came online and brought higher frequencies etc, i seem to recall novelty shops had a rack of objects one could attach to a phone. These would all light up when a call came in. There was apparently enough juice in the signal that the antenna in the object could drive a LED.
  - throwanem 9y ago
    Yup. It doesn't take much to make an SMT LED shine - just a milliamp or two, and an interesting property of that kind of inductive coupling is that, up to a limit, you can couple a higher voltage out of a given signal by increasing the number of turns in your winding. And if you couple out more than the forward voltage of your LED junctions, you can convert the surplus into enough current to visibly light the LEDs as they conduct. So with the right kind of boost circuit - in this application probably just an inductor, although I could be wrong here, analog isn't my forte - driving the LEDs, and a bare-die CMOS shift register that sips a few microamperes for the animation, you can pretty easily produce the kinds of effects I remember seeing back in the before time too - and still miss to this day! RFID works by the same principle, incidentally - in this case, the energizing signal comes from a primary winding in the reader housing, and the secondary in the card powers a little CMOS chip that in cheaper models just modulates the voltage drop over the winding to return a constant code, and in more expensive models receives a challenge nonce signaled by the card reader and modulates the winding to return an encrypted response. It's a really interesting application, and an impressive but often overlooked early example of "IoT" style smarts done well.
- thesmok 9y ago
  My friend's chinese motorcycle had this light built in on the gas tank. It's really helpful because you can't hear your phone ringing/vibrating while riding. AFAIK, this stopped working after transition to 3G.

by beala 9y ago

SOLAR_FIELDS 9y ago

I’m guessing car manufacturers have caught onto this. I drove a year 2000 car whose speakers would know I was about to receive a text/call several seconds before receiving it. I don’t think I’ve been in a model later than 2008 that’s had this problem. The noise, like the AOL dialup modem beeps, are one of those things that become cemented in your brain and immediately recall themselves as soon as you think about them. I heard the short succession of beep patterns in my head as I read your comment.

digi_owl 9y ago
That, and possibly that newer networks work on different frequencies.
- kalleboo 9y ago
  It's not that they use different frequencies (in a lot of places, they've actually recycled GSM frequencies for increased LTE bandwidth) but that they use a different form of modulation (than TDMA) that doesn't cause the same interference
robocat 9y ago
2G GSM? https://youtu.be/jBu1ILbIKZo https://youtu.be/jBu1ILbIKZo
- digi_owl 9y ago
  Makes a guy nostalgic for beach summers when the boombox would overlay that because someone left their phone to close to it.
- SOLAR_FIELDS 9y ago
  Yep that’s it. So it wasn’t the cars then, it was the networks being updated.

mavidser 9y ago

I remember old feature phones which had a fancy light on the back, which started blinking whenever a call was about to come through. Was a pretty nifty feature when you were expecting calls ['twas a time when I used to give "missed calls" for a callback].

digi_owl 9y ago
Before UMTS came online and brought higher frequencies etc, i seem to recall novelty shops had a rack of objects one could attach to a phone. These would all light up when a call came in. There was apparently enough juice in the signal that the antenna in the object could drive a LED.
- throwanem 9y ago
  Yup. It doesn't take much to make an SMT LED shine - just a milliamp or two, and an interesting property of that kind of inductive coupling is that, up to a limit, you can couple a higher voltage out of a given signal by increasing the number of turns in your winding. And if you couple out more than the forward voltage of your LED junctions, you can convert the surplus into enough current to visibly light the LEDs as they conduct. So with the right kind of boost circuit - in this application probably just an inductor, although I could be wrong here, analog isn't my forte - driving the LEDs, and a bare-die CMOS shift register that sips a few microamperes for the animation, you can pretty easily produce the kinds of effects I remember seeing back in the before time too - and still miss to this day! RFID works by the same principle, incidentally - in this case, the energizing signal comes from a primary winding in the reader housing, and the secondary in the card powers a little CMOS chip that in cheaper models just modulates the voltage drop over the winding to return a constant code, and in more expensive models receives a challenge nonce signaled by the card reader and modulates the winding to return an encrypted response. It's a really interesting application, and an impressive but often overlooked early example of "IoT" style smarts done well.
thesmok 9y ago
My friend's chinese motorcycle had this light built in on the gas tank. It's really helpful because you can't hear your phone ringing/vibrating while riding. AFAIK, this stopped working after transition to 3G.