This circuit uses a 555 (according to the diagram) to generate 50 ms tone bursts at a frequency of 1.5 kHz. The circuit is from an 80's Electronic Design.
June 2017 - Mouser Electronics has the new Texas Instruments OPA167x series operational amplifiers available...
This circuit was found in a 1977 Radio Shack documentation. The circuit is tuned to 1.4 kHz, but...
This simple CMOS touch switch was obtained in a 1987 publication. All components are common and the...