This circuit of an Electronics Hobbyists Handbook uses a different configuration for a triac. The circuit uses an integrated frequency divider and a coupler with a fotodiac.
With this circuit it is possible to control a relay up to 100 mA with an extremely low input...
The circuit shown by figure 1 consists in a Schmitt-Trigger using two common general purpose NPN...
This oscillator, from an old Argentine publication from 1973, uses the inductance of the 500 ohms...