This receiver uses old transistors that are equivalent to BC548 and BC558. The photo diode is of any type. The receiver can be used on a highly sensitive audio link.
This circuit was found in 1967 Philips documentation. It uses transistors from that time....
In current sensors such as the INA185 from Texas Instruments, protection against input transients can be...
This circuit converts sinusoidal signals to square. The upper limit of frequency is abour 100 kHz...