This circuit is from an old Electroics Now. Its purpose is to protect the fax and modem lines of two computers of the time. Suppressors are types of the time.
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....