In the original publication of the 90s a 556 consisting of a double 555 is suggested. The circuit drives a speaker with good power. The power transistor shall be fitted with a heat sink.
Using bipolar, FETs and unijunction this long-lasting timer can reach 10 hours with good quality...
The configuration shown is from the National Semiconductor Linear Applications Handbook. The...
This shield circuit uses a common CMOS port. The voltage depends on the interfaced logic. The...