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.
This amplifier with very high input impedance was suggested by Texas Instruments in a manual of...
Using only a ULN5804 integrated circuit, stepper motors up to 500 mA can be controlled from TTL...
Constant current sources are used in applications such as battery chargers, electrolytic tanks, etc....