Abstract: A sidetone optimization circuit (230) provides the capability to adjust sidetone level received at a telephone handset to a desired level. A noise source (204) generates a noise signal that gets filtered by filter (206) in order to provide band limited noise to a telephone interface circuit (202). Telephone interface circuit (202) provides a sidetone signal (210), also known as a trans-hybrid loss signal. The trans-hybrid loss signal is filtered at filter (212) and transformed to a DC level at detector (214). The DC level is then compared to a predetermined threshold at comparator (224), and a variable impedance circuit (218) is adjusted until the DC level reaches the predetermined threshold in order to achieve a desired level of sidetone.

Abstract: An electronic device such as a cordless telephone base station (100) includes a battery compartment (212) for storing back-up batteries. The battery compartment (212) has a cover (202) which prevents access to the back-up batteries. When the battery compartment cover (202) is attached, a safety interlock electrically connects the back-up battery contact terminals (204 and 206) found in the battery compartment (212) to the rest of the base station electronics 320. But when the battery compartment cover is opened, the safety interlock disconnects the battery terminals (204) and (206) from the rest of the electronics. In this way the base station user is protected from dangerous electrical shock which may become present at the battery contact terminals (204 and 206).