Found in a1967 Ferranti documentation, this circuit uses an operational amplifier from that time. The circuit uses a LDR as a sensor and has a null setting.
The circuit shown in figure 5 generates square signals based on a transconductance operational amplifier...
By adding a transistor to the output and some polarization features we can obtain a higher output...
Found in the 1990 special issue of Radio Electronics Experimenter magazine, this circuit uses an...