This circuit with different colored indicator LEDs has an expanded scale. We found it in the March 1992 Radio Electronics magazine. For an adjustable range of 0 to 10.5 V.
This high selectivity circuit for single tone decoding was found in 1970s documentation. The coil...
The figure shows how to obtain a higher output current for an operational amplifier. With the...
This amplifier for hearing aid was found in a 1968 documentation using an integrated of the time....