This circuit was found in the February 1992 issue of Radio Electronics magazine. The circuit provides stepped frequencies as shown in the diagram.
Found on an 80's Radio Electronics, this circuit is designed to pass the 300 to 34,000 Hz voice...
The Texas Instruments INA826S Instrumentation Amplifier Evaluation Module is available from Mouser...
November 2016 - Texas Instruments' new TLV8802 nano-power operational amplifiers for wireless...