This circuit is from a 1969 Electronics World. The transistors may be modern general-purpose equivalents. The circuit is for frequency ranges between 250 Hz and 250 kHz.
This precision circuit was found in ancient American documentation. The most critical component is the...
Using an LDR, this Philips circuit directly activates a relay when light strikes the sensor. The...
This circuit can be used to obtain control signals from an infrared emitting source. The circuit is...