Smart Parking System

An eight-spot garage run by an FPGA, with an Arduino watching for fire

A gate controller for a small garage, built on a DE10-Lite FPGA. A VHDL state machine reads two IR sensors to tell a car entering from one leaving, debounces them, and keeps the count of free spots — eight at most — on a 7-segment display. An Arduino Mega reads an MQ-2 smoke sensor and, above a threshold, forces the gate open and sounds a buzzer, overriding whatever the state machine is doing. A voltage divider steps the Arduino's 5 V signal down to the FPGA's 3.3 V.

Procedure

4 min

What it does

A garage with eight spots, one gate, and a servo to lift it. Two infrared sensors sit on either side of the gate — one outside, one inside. From the order in which they trip, the system knows whether a car is coming in or going out, opens the gate for exactly as long as the car needs, and keeps a running count of free spots on a 7-segment display. When the garage is full, the gate stays down.

The whole thing runs on a DE10-Lite board with an Intel MAX 10 FPGA, written in VHDL. An Arduino Mega sits beside it doing one job: watching for smoke.

Two sensors, one state machine

The gate logic is a finite state machine that reads the pair of sensors as a two-bit value — outer, inner. The trick is that a car crossing the gate always trips the sensors in sequence, so the sequence tells the direction.

State	What it is waiting for	What it does
Waiting	The outer sensor to trip	Keeps the gate closed
Entering	The car to clear the inner sensor	Gate open; counts one spot down when the car is fully through
Exiting	The car to clear the outer sensor	Gate open; counts one spot up when the car is fully through
Wait for clear	Both sensors to read clear	Holds the gate open so it cannot drop on a car

The count only changes once a sequence completes. A car that pokes past the outer sensor and reverses out never touches the counter, and neither does a hand waved in front of one sensor. The “wait for clear” state is the safety net: whatever else is happening, if either sensor sees something, the gate stays up.

Infrared sensors are noisy — a passing car produces a burst of on-off flicker rather than a clean edge. A debouncing stage in VHDL ignores anything shorter than a set number of clock cycles, so the state machine sees one clean transition per event.

Manual control

A push button on the board opens the gate by hand. Two rules apply. The button goes through a 50 ms debouncer, so one press is one press. And the button is ignored when the count reads zero: a full garage cannot be opened manually, only exited.

When there is smoke

The MQ-2 sensor is an analogue gas sensor, and the FPGA board has no analogue inputs, so the Arduino reads it. When the reading crosses 300 the Arduino raises a single digital line to the FPGA.

On the FPGA that line outranks everything. Whatever state the machine is in, the gate opens and a buzzer sounds. The count is left alone; the point is to get cars out, not to keep score. The Arduino holds the line high for at least three seconds after the last reading over threshold, so a flickering sensor cannot make the gate stutter.

Two voltages on one wire

The Arduino runs its logic at 5 V. The FPGA’s general-purpose pins are rated for 3.3 V, and driving them at 5 V would damage them over time. The smoke line therefore passes through a voltage divider — 10 kΩ and 20 kΩ — that turns the Arduino’s 5 V high into roughly 3.3 V before it reaches the FPGA.

In the box

The gate is an SG90 servo; the sensors are two IR obstacle modules and one MQ-2. The VHDL is split into the main control file, with the state machine, debouncer, and counter, and a small 7-segment driver that only needs to show zero through eight. The repository has the sources, the pin assignments for the DE10-Lite, the full report, and two videos — one of the system running, one of the simulation waveforms.