This circuit was obtained from HAM Radio magazine in an 80's issue. The FETs are types of the time and the frequency is determined by the crystal. The circuit operates at voltages from 3 to 9 V.
This timer with 1 second accuracy was obtained in a 1973 documentation. The Buzzer is a low-power type...
The sensors in this circuit are NTCs and PTCs that work in a differential way by directly...
The presented circuit is suggested by Texas Instruments (www.ti.com) in its Application Report...