This circuit was found in documentation from the 1970s. However, it can be implemented with modern transistors such as 2N2222 for Q1 and BF494 for Q2. The crystal depends on the desired frequency.
The circuit shown in the figure is suggested by National Semiconductor and makes use of an...
We found this circuit in an old Mullard (Philips) documentation. The sensor consists of a...
This circuit is from 1987 documentation. The operating system used is not common today, but two...