Single-Chip Melody Generator

Cl D1 10n 15n 22n (loon R2 LSLK en 01...03 = 1N4148 BC547 T2 N1...N4 = ICI = 4093 R8 "Cl C8 0W5 R3 R4 00 135 057 SINGLE-CHIP MELODY GENERATOR C5 C6 C7 70n 110n To BC557 T1 13 0 20mA 3V This melody generator, based on a Type 4093 CMOS Schmitt trigger, may be used in alarms, doorbells and cars (audible reverse gear or lights on indicator). Three of the four NAND gates in the 4093 are con- nected in series by RC networks. Oscillation is effected by feedback of the output signal of N4 to the input of N2. The logic high levels produced by the cascaded gates in the oscillator circuit are used for biasing one of associated diodes D1, D2 and D3. The relevant diode connects one of frequency-determining capaci- tors Cl-C3 to tone oscillator N1. The audio signal available when S1 is pressed is applied to comple- mentary transistor pair T1-T2 that drives the loud- speaker. The frequency of the emitted tone may be adjusted to individual taste by preset P1. On 894002-11 C) GENERAL INTEREST