Earphone A transducer which converts electrical energy to sound.
Aerial (Antenna) A device to receive or transmit radio signals. It is also known as an antenna.
Ammeter Measures current.
Logic gates process signals which represent true (1, high, +Vs, on) or false (0, low, 0V, off). For more information please see the page on logic gates. There are two sets of symbols: traditional and IEC (International Electrotechnical Commission).