4 ms·

> The only downside is that external light can actually affect the chip operation (light hitting the die releases electrons at PN junctions creating errors in c

> The only downside is that external light can actually affect the chip operation (light hitting the die releases electrons at PN junctions creating errors in circuit operation ) .. .however here the Faraday metal shield helps prevent this. Brings me back to when it was discovered that high intensity flashes could make a Raspberry Pi 2 reboot...[1] [1] https://www.raspberrypi.com/news/xenon-death-flash-a-free-physics-lesson/ https://www.raspberrypi.com/news/xenon-death-flash-a-free-ph...

squarefoot 5y ago
Many PN junction based components such as diodes and transistors are photosensitive; I recall after reading this as a kid on an old electronics magazine, I took a 2N3055, a pretty common power bipolar transistor back then, uncapped it to expose the die then connected it to my analog tester and saw it generating current when exposed to a lamp. The effect is common also in devices one could never suspect to be sensitive to light such as LEDs. They can produce light but also detect it. A few years ago someone published a project online of a MCU based keyboard (actually a button board) made of PWM driven LEDs that can both produce light and during their off cycle detect it, so that one turns them on and off just by touching them with a finger screening them from surrounding light. I attempted to search for that project without luck.
- daniel_reetz 5y ago
  I remember that project too. Might have been Paul Dietz at MERL.If you're curious, look up Paul Dietz "low cost bidirectional sensing using LEDs" and Forrest Mimms "LED Sun photometry".
  - jacquesm 5y ago
    > Forrest Mimms There's a name I haven't seen in a long time. Source of endless insight into electronics parts and schematics.
    - avhon1 5y ago
      He did a series of columns for Make Magazine. A compilation book titled "Make: Forrest Mims' Science Experiments" was published in 2016. https://www.makershed.com/products/forrest-mims-science-experiments https://www.makershed.com/products/forrest-mims-science-expe...
- dangets 5y ago
  A self-directed project I did for a university course was to make a Morse code transmitter and receiver. I was able to use the same LED for both.
  - adolph 5y ago
    By using the same LED as a receiver too? https://makezine.com/projects/how-to-use-leds-to-detect-light/ https://makezine.com/projects/how-to-use-leds-to-detect-ligh...

squarefoot 5y ago

Many PN junction based components such as diodes and transistors are photosensitive; I recall after reading this as a kid on an old electronics magazine, I took a 2N3055, a pretty common power bipolar transistor back then, uncapped it to expose the die then connected it to my analog tester and saw it generating current when exposed to a lamp. The effect is common also in devices one could never suspect to be sensitive to light such as LEDs. They can produce light but also detect it. A few years ago someone published a project online of a MCU based keyboard (actually a button board) made of PWM driven LEDs that can both produce light and during their off cycle detect it, so that one turns them on and off just by touching them with a finger screening them from surrounding light. I attempted to search for that project without luck.

daniel_reetz 5y ago
I remember that project too. Might have been Paul Dietz at MERL.If you're curious, look up Paul Dietz "low cost bidirectional sensing using LEDs" and Forrest Mimms "LED Sun photometry".
- jacquesm 5y ago
  > Forrest Mimms There's a name I haven't seen in a long time. Source of endless insight into electronics parts and schematics.
  - avhon1 5y ago
    He did a series of columns for Make Magazine. A compilation book titled "Make: Forrest Mims' Science Experiments" was published in 2016. https://www.makershed.com/products/forrest-mims-science-experiments https://www.makershed.com/products/forrest-mims-science-expe...
dangets 5y ago
A self-directed project I did for a university course was to make a Morse code transmitter and receiver. I was able to use the same LED for both.
- adolph 5y ago
  By using the same LED as a receiver too? https://makezine.com/projects/how-to-use-leds-to-detect-light/ https://makezine.com/projects/how-to-use-leds-to-detect-ligh...