Integrating RF LED Detector
Burkhard Kainka
Using a given microcontroller system my question was: How can I make the simplest
possible RF receiver. I am using the ATtiny13 on the Sparrow board. LED2 is connected
to port B.3 which is ADC(3) as well. So why not connect an Antenna here. The LED should
work as a detector diode. A bias voltage is needed. So I should switch on the internal pullup.
To get it sensitive enough I had to use one more trick. I switch on the pullup for a very
short time. This will charge the LED which is also a little capacitor of only a few
picofarads. Voltage may rise up to 2 V. Then I switch back to high Z. The LED is
discharged down to about 1.5 V after some microseconds. But in the presence of an
RF signal is will discharge a little lower. Several RF pulses may result in an
integrated loss of LED voltage. That’s why I call it an integrating RF detector.
In the end I need something like 50 mV at 100 kHz the get a clear result.
I used Basom to program the Tiny13. I used an integration time of 10 µs. At the
beginning I collect a reference value Ref to know the LED voltage without signal.
This is used later to detect the voltage loss caused by an RF signal.
Quelle: