This circuit was obtained in a Popular Electronics of the 90s. The circuit uses integrated from the time, uncommon today. Note that the speaker has a higher impedance than ordinary speakers.
This small transmitter with 2 transistors can reach several hundred meters using a 30 to 70 cm...
This circuit was obtained in a 1977 Radio Handbook. The transistor is from the era and the coils...
This charger can be used with one to four AA, AAA, C or D cells. The maximum current is given by R...