Audio Input Selector

This circuit, designed for audio applications, allows the user to select which input signal will be enabled when the system is switched on. The setting is not fixed, but is stored in an EEPROM which is read when power is applied. Fortunately, because of the falling price of EEPROMs, this is not an expensive proposition. The switch used here is a shaft encoder with rotation outputs and a pushbutton (Conrad Electronics catalogue number 70 55 94).