Musical door bell / Muzaini Mansor and Shamsudin Abdullah

This musical door bell generates 16 difTerent notes in three second, and repeals the cycle for about ten second when the ’press switch ofT is pushed momentarily."Hie unit works of four CD size preferable cells(16V),and it does not require on/off switch as the ideal current is less than 40 micro amperes.
The circuit for musical door bell comprises a clock oscillator using popular timer IC 555, 4-bit binary counter 7493 and digital analogue converter using four resistors. Basic audio oscillator using IC 555(IC 3),and an electronic delay switch