Practical problems
Problem 1
In a bank there is a safe the keys for which are possessed by a manager and his three deputies.
On working days (Monday to Saturday) between 8 a.m. and 3 p.m. the safe can be opened
with the keys of at least two deputies or with the manager’s key. On Sundays, in the same
hours, to open the safe you need the keys of all three deputies or the manager’s key. The safe
can always be opened using all four keys (on any day and at any time). Assuming that
appropriate date and time signals are available, design a digital circuit which controls the lock
of the safe. Try to minimize the system but do not use the K-map method for more than four
variables.
Problem 2
There are ten floors in a building (levels 0 – 9). The building’s elevator system has ten position
sensors, one at each level. The sensor is activated (outputs logic 0) when the elevator reaches
the given level. Design a system that displays in decimal on which level is the elevator. Use a 7segment display with common anode (google the Internet for necessary information about
this display).
Problem 3
Design a microwave controller. The oven has a thermometer with WH and WL outputs. WH is
active when the temperature inside the microwave exceeds maximum temperature, TH.
Similarly, WL is active when temperature drops below TL. The controller should turn the
microwave on when T < TL and turn it off when T > TH. If the temperature is between TL and TH,
the controller should not change the power switch position.
Problem 4
Draw the STD of a simple car alarm controller. The system has one input Y, which is connected
to the car's door switch, and one output Z, which is used to operate a relay that honks the
horn by shorting the wires that go to the horn switch in the steering wheel. The system is
asynchronously reset by the accessories power line that is high when the ignition is turned on
or is in accessory-only mode, both of which require the key to the car.
Arming the alarm: removing the key, opening the door for at least one clock cycle (5 seconds)
and closing the door. Disarming the alarm: opening the door and inserting the key into the
ignition switch. Activating the alarm: opening the door and not inserting the key into the
ignition switch within 3 consecutive clock cycles, i.e. within 15 seconds.