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 is based on the HA1311 integrated circuit, common at the time the article was...
This circuit consists of a low-pass filter for the frequency of 440 Hz. The filter therefore...
This circuit was obtained from a Radio Electronics magazine from June 1969. The circuit uses a...