LIFT

Fig. 1: Schematic of physical model

Lift Project is one of the projects designed in department of computer engineering at TTU as a lab project. The main task in this lab is to design a controller for an elevator. Goals of this lab are:

• to undrestand Finite State Machine (FSM) design

The process of this lab is described in Fig. 1. Students first have to describe the controller by providing FSM diagrams and transition tables to the staff and then go through a process of implementation, synthesis and verification. In the end they are required to submit a report.

Physical Model

Fig. 2: Schematic of physical model

This model has 5 floors but the last floor is reserved for security reasons.The schematic of the model is shown in Fig. 2. Each floor has a sensor and on the top floor there is an emergency break that stops the cabin from going through the roof. There is no elevator door included in the model at the time of writing this document.

Lego Construction

based on the task specifications a lego model has been built for this lab.

Controller circuit

The controller circuit is equipped with an FPGA and is monitoring sensor behaviour and issueing control signals to motor driver circuit based on the calls it gets from inner and outer cabin buttons.

first prototype

In the first verion of control board, a XULA fpga board has been used (XULA board reference manual). Pin configuration of this board has been shown in Fig. 3.

Fig. 3: Schematic of control board

The first prototype control board provides the following functionalities:

• Seven segment display
• Infra Red (IR) sensors at each floor
• Inner and outer cabin push buttons
• Motor state indicator LEDs
• Software reset button
• Hardware break at top floor

System Components, Signal Names and Description

Fig. 4: System Components

Top level design entity that students are required to design's interface has been described in the table below:

Name	Port	type
clk	in	STD_LOGIC
sensors	in	STD_LOGIC_VECTOR (4 DOWNTO 0)
calls	in	STD_LOGIC_VECTOR (4 DOWNTO 0)
menu	in	STD_LOGIC_VECTOR (4 DOWNTO 0)
motor	out	STD_LOGIC_VECTOR (1 DOWNTO 0)
sleep	out	STD_LOGIC
Seven segment	out	STD_LOGIC_VECTOR (6 DOWNTO 0)

The control system itself has different components that have been shown in Fig. 4. In this figure:

• Counter is a 24 bit counter in the design.
• Sensors should be designed according to the following functionality (see Fig. 5):

• • Sensors are prone to bouncing because of vibrations in the lift which might not be visible to the naked eye but is visible to the sensors. Hence the sensors need to be de-bounced by a three bit shift register with 19th bit of counter slowing the de-bouncing circuit.
  • The lift has five ray cut Infra-Red (IR) sensors.
  • When ever a sensors ray is cut by the lift it sends a signal '1' to the FPGA. Otherwise the sensor sends a '0'
  • Each sensor is placed between floors and there can be blind spots between each sensor. When the lift is in a blind spot all sensors send "00000" to the FPGA. This is the time when the lift is moving between two sensors. At this point sensors can also recieve value from two sensors as well. (e.g. on the second floor sensors can either have a value "00000" or "00110".) It is recommended that both cases should be handled by the designer. (hint: rather then looking for sensor ="00100" look for sensor(2)= "1".)
• Motor should be controlled in the following manner by motor FSM (see Fig. 6)
  • Motor(0) controls the direction of the motor. Where '1' is DOWN '0' is up
  • Motor(1) generates a clock signal which controls the speed of the motor. The speed is specified by a clk like signal by changing its frequency. The recommended speed of Motor can be given by sending 10th bit of the counter.
  • A sleep signal turns off the motor. In idle state the motor should be kept turned off. where '1' is ON and '0' is OFF
  • Motor FSM should also shares its Status with Floor FSM ( i.e. idle, going up, going down, blinking Seven segment)
• Seven segments should work as follows
  • Seven segment decoder decodes the current floor into seven segment output.
  • while designing 7seg decoder you should keep in mind that unlike seven segments on Nexys FPGAs you do not need to specify the anode.
  • Each segment is turned on by logic value 1. Seven segment should also be able to blink 5 times after it reaches a floor.
  • Unlike nexys 2/3 board's seven segment the pin orientation is opposite. (i-e. seven segment <= "abcdefg";)
  • When the elevator reach a particular floor then it should stop and blink the floor number for 5 seconds.
• The Floor FSM should work in the following manner.
  • FSM floor calculates the current floor based on the sensor and the Motor FSM status (direction sleep).
  • The sensors have blind spots Hence the floor FSM should remember its own floor while passing through the blind spot

Fig. 5: Sensor setup on the lego structure

Fig. 6: Stepper motor setup in lego model

Fig. 7: First control board prototype

The UCF File

The following code is the UCF file for XULA board:

NET "clk" LOC = P43;
NET "m0" LOC = P56; # Direction 
NET "m1" LOC = P13; # step clock
NET sleep LOC = P44; # sleep to disable the motor

NET "ss(6)" LOC = P37;
NET "ss(5)" LOC = P36;
NET "ss(4)" LOC = P57;
NET "ss(3)" LOC = P61;
NET "ss(2)" LOC = P62;
NET "ss(1)" LOC = P50;
NET "ss(0)" LOC = P52;

NET "calls(0)" LOC = P21; 
NET "calls(1)" LOC = P32;
NET "calls(2)" LOC = P33;
NET "calls(3)" LOC = P34;
NET "calls(4)" LOC = P35;

NET "menu(0)" LOC = P3;
NET "menu(1)" LOC = P4;
NET "menu(2)" LOC = P7;
NET "menu(3)" LOC = P19;
NET "menu(4)" LOC = P20;

NET "sensors_in(0)" LOC = P39;
NET "sensors_in(1)" LOC = P68;
NET "sensors_in(2)" LOC = P82;
NET "sensors_in(3)" LOC = P97;
NET "sensors_in(4)" LOC = P94;

Safty Monitoring Mechanism

Since this model is designed to be controled remotely, it should be able to maintain its functionality even if it is programmed with a faulty design. For this reason we need some monitoring system to guarantee the functionality.

hardware break

A physical switch has been installed on the top floor to prevent faulty designs to go through the roof.

behaviour monitor

Since reaching hardware break will require human intervention and it would not always possible (in times that an operator is not present etc.), a behavior monitor system has been added to the lift. Motor control signals goes through the monitoring system and if it detects a suspicious behaviour (being on first floor and unwinding the thread or being on the top floor and trying to move up) it takes over the control and brings the lift to the initial position and sends a reset signal to the control board.

Testing

After students finished their design they are required to perform tests on their designs firs by simulating it and then try it on the physical model.

Simuation

VHDL Simulation

A VHDL testbench has been designed to be used for verifying the functionality of the lift.

Verilog Simulation

Students are required to write a Verilog testbench to test their designs.

Remote Lab

in this project, a remote lab was designed for students to access the controlling hardware from any remote place inside the department INTERA network. The server is running on a raspberry pi and students can see a view of the working lift using an internet camera. A working sample of the controller is provided to the students as a demo in order to get them accustomed to the functionality of the Lift. you can access this lab from this link: cherry.pld.ttu.ee

Web Server

• Server on Raspberry Pi
• Username and password for restrictions on access
• Internet webcam

Push button emulator

Raspberry Pi GPIO's have been used for emulating push button behaviour.

Lab Reports

Students are required to submit a report in the beginning before starting their designs to describe the process of what they are planning to do and one at the end of the lab along with their codes. A lab report template has been provided for students (You can find it here: File:lab6_template.pdf) and all the reports should be submitted in the same format.

Future plans for improvement

• queueing system for login in remote lab
• checking the bitfile for malicious code
• making a 3D model for printing
• providing access for students outside ATI interanet
• PCB design for control board
• adding a micro-controller based control board
• monitoring all the sensors in monitoring system