For this homework assignment you will design a circuit that uses a transistor like an ON/OFF

switch to control the flow of current through a relay's coil. When the transistor turns ON

(saturation) current flows through the relay's coil and produces a magnetic field that

actuates the relay's electro-mechanical switch contacts (they are brought into contact, or

"closed") thereby turning the relay's mechanical switch ON. Likewise, when the transistor

turns OFF (cutoff), current flowing through the relay's coil drops to zero Amps, the magnetic

field around the relay's coil collapses, and this deactuates the relay's electro-mechanical

switch contacts (the contacts are pulled apart, or "opened"), thereby turning OFF the relay's

mechanical switch. The control signal that turns the transistor ON/OFF is supplied by a

digital output pin on a microcontroller. When the microcontroller produces a logic HIGH

output at a digital output pin, this output signal this turns the transistor ON (saturates);

likewise, a logic LOW output signal at the digital output pin turns the transistor OFF (cutoff).

HINTS

When two single-pole (SP) switches are mechanically ganged together so that both switches actuate

together (at the same time), this type of switch is described as a double-pole (DP) switch (a.k.a, a 2-

pole switch). When three SP switches are mechanically ganged together, that switch is called a triple-

pole (TP) switch (a.k.a., a 3-pole switch), and so on.

The relay's coil designation is categorized as a single side stable.