This circuit from Popular Electronics powers a small speaker. The transistor can be of general use and the capacitors can be altered to change the sound generated.
This circuit is from a Radio Electronics magazine from August 1990. The indicator module is of a...
This flip-flop using two bipolar transistor was found in a publication of the year 1968. The...
This TTL siren is formed by two oscillators using each two Gates of a 7400. Frequency or the...