We found this circuit with JFETs in a Radio Electronics magazine from June 1969. The circuit has its assembly described in a complete article. Equivalent transistors can be used.
The frequency of this circuit is approximately 1 Hz. Whenever the output is at low level, the LED...
This circuit can be used in a digital measuring or shield interface. The circuit is from old...
In the figure we show how to implement a TTL photo-trigger with the 7413. This circuit can be used...