This sensitive two-transistor circuit was found in the June 1965 Radio Electronics magazine. The circuit has low drift and uses an analog instrument. The input resistance is high.
This circuit was suggested by Motorola in its manual of components for optoelectronics (1987)...
This sweep oscillator was found in 1980s American documentation and can be assembled with current...
In the figure we have a low-pass filter, with a cutoff frequency of 10 kHz, also suggested by...