We found this circuit in the November 1984 Radio Electronics magazine. The base frequency is given by C1. The power supply can be between 3 and 12 V.
This is a combined circuit of tone generator and preamplifier. We found it in a 1975...
We found this simple alarm circuit in a 1986 documentation. The circuit uses sensors of the NA...
We found this circuit in the Linear Applications Handbook by National Semiconductor. The base is...