I lay imported electronic wrist watch in metal case with a faulty indicator. Names hours a lot of this type (for example, "Montana"), but they're all the same. At the current time on the display, the melody is activated by pressing and holding the button "AL.TM" and momentary - on, click "DATE". This principle is implemented in the call. The clock battery is replaced by an element A343, it lasts for several years. Element it is best to solder, because "-" often the salt and it is oxidized. Instead of a piezo oscillator necessarily turns on the load - capacitor C1 type km (between the watchcase and the "spring").
(Click to enlarge)
Added amplifier transistor type CT (CT) with a large Insert, the load of which is the speaker 0.5 watts, 4 Ohms. And for some hours the volume was insufficient, had to add an additional amplifier to CTD. The PSU is the simplest rectifier 15 In with a permanent connection of the primary winding to the network. Because some of the tunes have a great time, which is undesirable for a call, it is complemented with time relay, limiting the playing time to a few seconds. Diagram taken from [1]. The establishment of a time relay.
Literature
Author: K. Kulikov, Samara; Publication: N. Bolshakov, rf.atnn.ru