We found this configuration in a 1990 Poptronics. The circuit can be powered by voltages between 6 and 15 V, changing the resistors in series with the LED. The frequency is set at R7.
This circuit shows on the screen of an oscilloscope two signals alternately at a frequency that depends...
This circuit is from a Radio Electronics from August 1992. The transistor used allows the control of...
This circuit measures the strength of audio signals. We found it in an American publication from...