Want to make some stuff that fits your car or motor cycle? Then here is a simple musical horn circuit that can be connected to the 12V battery of any car or motorcycle. This circuit commonly used as reverse musical horn. Here we use a commercially very low cost musical IC UM66. But this Ic can only handle supply voltage below 4V. So we used a 7805 regulator ic for adjusting the voltage to 5V and its further reduced to 3.8 volt by connecting two diodes D1 and D2 then it will supplied to musical horn producer UM66.
Whenever we supply a 12v to the musical horn circuit, it will always produce music. So we need to connect a switch between battery and circuit and when you want to move on reverse gear, the switch must be pressed to produce music.( You can setup the circuit to automatically plays sound while reversing the car but it requires more skill to implement)