Two simple audio hobby project as discussed here for the electronic enthusiasts, the first one is a simple electronic audio input selector switch and the other one is an interesting sound activated switch.
Four different inputs can be switched through by the continual pressing of SW1. lC1 is a dual ‘D’ type flip flop. The O outputs are connected to the D inputs so that the clock inputs are divided by two. The two flip—flops are connected in series, giving a two stage binary counter. lC2 is a quad OR gate. This is used to decodethe four states of the counter. The outputs are used to control the quad switches of IC3 and lC4·(4016AE).
Contacts X_-X and Y-Y of the relay are normally open. When the relay is energized, current flows through SW1, X·X and R5, thereby locking on the relay. At the same time contacts Y—Y close and current from the secondary of T2 is available at the extension lead sockets, to operate the remote bell or lamp. lf the ‘lock—0n switch SW1 is open, contacts Y-Y open when the sound ceases, and this is satisfactory if thewarning lamp or bell is likely to receive immediate attention. The pilot lamp LP1 is of aid when setting ,. the unit, as with SW1 open it will, show at what sound level operation is being obtained. For occasional use battery opera-tion is possible by omitting the silicon rectifier D1, C5 and transformer T2. A 9V battery is connected to the positive and negative points shown, with an 0n—0ff switch in circuit.
Quiescent current is about 6mA, which is not very heavy and will allow a long period of working from a PP9 or similar battery._ The two flip—flops are connected in series, giving a two stage binary counter. IC2 is a quad OR gate. This is used to decode the four states of the counter. The outputs are used to control the quad switches of IC3 and IC4· (401 BAE).