This circuit was obtained from an American 1980s documentation. The frequency depends on the crystal and the circuit may be a PNP that reaches the generated frequency.
In the circuit shown in the figure we have the way to excite a small speaker from a TTL output. The...
This high frequency modulator was found in Motorola's 1990 Linear Databook. The current depends on the...
This ground-based circuit was found in 1990s American documentation. The transistor can be any...