3 ms·

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

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.

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.