► Schematic diagram of the
circuit
►
Design calculation
- 1st OP Amp
It
produces a voltage signal that proportional to the current flow over the
phototransistor, which minimum value is biased by non-inverting input voltage
2.452V.
- 2nd OP Amp
It
amplifies the voltage signal from 1st OP Amp using open-loop voltage
gain. In this amplification, the input voltage under 2.548V makes 0V output,
and input voltage over 2.548V makes the saturation OP Amp voltage, about 4V in
this case
So, this OP Amp nearly amplifies only high
time signal in 1st OP Amp, which means the duty of beacon, because
the bias voltage difference between two OP Amps is very small.
- Hex Inverting Schmitt Trigger
It
produces 0 or 5V signal which is suitable for micro processor input according
to 
from 2nd OP
Amp.