This circuit, which controls both the temperature and the level of a liquid in a reservoir, was found in an Electronic Design from the 90s. The circuit is based on a double 555.
We found this circuit in the Linear Applications Handbook of the National Semiconductor of 1994....
This transmitter can send its signals from several kilometers away, depending only on the antenna...
Found in the November 1974 issue of Radio Electronics magazine, this circuit has a frequency range...