Wi­Fi Connected Locker Access System

Problem Statement

Senior Design teams at Iowa State store their projects in the Senior Design lab in lockers secured by padlocks. These locks are reused semester after semester and previous students may remember their locker combination for the sake of tampering with current student’s projects. Additionally, administrators have the maintenance overhead of manually assigning lockers to students. This is unacceptable, as students spend hundreds of hours and hundreds of dollars on their projects, and the senior design lockers must be as secure as possible.

Solution Statement

The solution, which is extensible, reliable, and affordable, reprises the current system to utilize electronic lockers, complete with remote management. These lockers are battery powered and access is provided using current student’s ISU ID cards. Groups may also be assigned a username and password to access their lockers under the case that individual students forget their ID card.

This solves the aforementioned issues by securing the lockers to the point where previous students cannot access current lockers, and administrators can easily install or alter lockers, saving both time and money.

System Level Design

System Requirements

Functional Requirements

● System shall read student’s ISU ID Card, providing access on a single swipe
● System shall have a keyboard failback, such that students without ID Cards may still
access the system
● System shall allow administrative functionality, both local and remote, including
altering access lists and overriding functionality
● Wireless transmitters should securely transmit data, ensuring only secure access to
● LCU (“Locker Control Unit”) shall be secure, in that only a valid signal from the MCU
(“Main Control Unit”) will open the lock
● The MCU must store usernames/passwords/groups of users, and be easy to remotely
manage to alter information
● The MCU must be “locked­down”, such that non­administrative users cannot alter or
access any information

Non­Functional Requirements

LCU shall be battery­powered and last a minimum of two full semesters
● The LCU batteries should supply at least 4 volts of power until shutdown event
● The LCD display on the MCU shall display when locker batteries are below 20% and
are in need of replacement
● The LCU, low­power, red LED shall illuminate every 5 seconds when batteries are
below 10% power
● The servo should be able to hold open the lock for at least 10 seconds
● The locker shall re­lock 10 seconds after it has been unlocked.
● The LCU green LED shall illuminate when the locker has been unlocked.
● The MCU must connect to Iowa State public Wi­Fi, and must automatically connect
after a reboot
● The MCU must allow incoming SSH connections
● The MCU must reject foreign input
● The MCU must display a status report on valid administrative SSH login
● The MCU must be able to control lockers a maximum of the distance of the room
● The LCU shall have a physical key that will manually unlock the lockers for cases in
which batteries have died

Operating Environment

The current solution assumes a standard environment of a classroom or workplace, where general secure access is assumed. Users would be able to safely store personal items in a designated locker with an automated lock. This lock is controlled by the swipe of an id card. The user would be able to either swipe their personal card or type their group username/password into a designated keyboard. This control of access to the lockers is determined by the credentials stored on the MCU located in the room. Additionally, it is assumed that the lockers are stored in a stable operating environment in a temperature­controller room. As general secure access is also assumed, no physical security shall be implemented to the controlling units beyond a standard casing unit and lock. Additionally, it is assumed that the environment is weather­controlled and is not be exposed to the elements.

In more detail, the following environmental conditions are assumed:
● Temperature ranging from 65 degrees fahrenheit to 75 degrees fahrenheit
● Locker dimensions 4’ x 5.5’ x 17’’
● Room dimensions 44’ x 28’
● Several room obstacles, hindrances, and blockages of varying materials that obstruct
wireless signals

Intended Users and Uses

The intended users for this product are students enrolled into Senior Design for the ECPE department at Iowa State University. Additionally users include management staff, who will remote into the MCU (“Main Control Unit”) to manage the system by adding/removing user accounts to lockers, and managing battery supply units.

The lockers themselves are “Bolt­Cutter safe”, in that they are designed around the same difficulty as bringing a pair of bolt cutters into the room and cutting the doors off manually. As such, the lockers are intended to be secure from most standard means of digital cracking, and they shall also be physically safe from all but the persistent in physical damage.

Block Diagrams of the Concept

Figure 1, Concept Block Diagram of Project

All components to the left of “WIRELESS” are considered parts of the LCU and all components to the right of
“WIRELESS” are considered parts of the MCU

Figure 2, Block Diagram of Project with interconnections

All components to the left of “WIRELESS” are considered parts of the LCU and all components to the right of
“WIRELESS” are considered parts of the MCU

Detailed Implementation

I/O Specification

The input and output shall be as follow:
● LCD display on the MCU (“Main Control Unit”) shall render username/password
information, and display success/fail on opening a locker
● LCD display on the MCU shall render, specifically, which LCU’s have critical battery
● When the LCU receives a correct signal from the MCU, the corresponding locker
should unlock for 10 seconds and a green LED should illuminate during this time to
indicate that the locker can be opened
● When battery power is at 10% a red LED shall illuminate, every five seconds, on the
LCU to indicate that batteries are critically low and need to be replaced.
● Magnetic­strip card reader
○ Reads ISU ID Card, providing information on magnetic strip
● Full qwerty­style keyboard for username/password entry
● Remote­SSH management input

Circuit Specifications

Power Circuit and Design

The power sources for the LCU (“Locker Control Unit”) are batteries. The project will be using four 1.5 volt ‘Energizer max AA’ batteries to power the ATMEGA328, servo, and Xbee units. From the current draw calculation it was calculated the required milliamp hours needed to keep the system running, as seen below. The results were then compared with three different types of batteries: Energizer ultimate lithium, Energizer Max, and Energizer rechargeable. The Energizer max provided the best cost/performance ratio with the minimum capacity, which is why it was chosen to power the system.

The battery chosen has a 7 year shelf life at 21 degrees celsius. The typical weight is 23 grams, and typical volume is 8.1 cubic centimeters. It can operate at 0 degrees F to 130 degrees F. Below are the battery dimensions taken from the data sheet:

Atmega to Servo Circuit Specification

The I/O of the servo is controlled by the ATMEGA328. The servo is powered from the batteries, through a transistor, to conserve power. When the ATMEGA receives the command to move the servo, it sends a signal out pin 15, which is a PWM pin, on the ATMEGA328. The ATMEGA is programmed to rotate the servo to the desired location depending on the width of the pulse the ATMEGA sends out of pin 15. Furthermore, when the servo receives the command to move, a 5V signal is sent out of pin 14 to switch on the transistor. When the servo is not sent a signal to move, pin 14 is left floating and the 10k pull up resistor pulls the NPN base voltage up to 6V, which turns the transistor off. This causes the servo to only be powered when instructed to move, saving power.

Figure 3, Atmega to Servo Circuit Schematic

Atmega to Visual Output Specification

The visual output (Bi­LED) is controlled by pins 18 and 19 of the ATMEGA328. When the ATMEGA receives the signal to illuminate the green LED it sends a signal out of pin 18. Alternatively, when the ATMEGA receives the signal to illuminate the red LED it sends a signal out pin 19.

Figure 4, Atmega to Visual Output Circuit

Atmega to Xbee Circuit Specification

Figure 5, Atmega to Xbee pin layout

There are only two pins of ATMEGA328 connected to the two pins of the Xbee. The pins of ATMEGA328 are PD0 (RXD) and PD1 (TXD) whereas the pins of the Xbee are ‘Dout’ and Din’. The ATMEGA328 and Xbee are connected to the 5V (‘Pin’ VCC) and 3.3V (‘Pin’ VDD) voltage supply respectively.

Pi to Xbee Circuit Specification

The Raspberry Pi and the Xbee unit are connected to each other with a single micro­usb cable. The Raspberry Pi operating system then autodetects a new serial device, and registers it to a default port (typically ‘/dev/ttyUSB0’, however USB1 and USB2 are also common). The Raspberry Pi server is configured to accept only input on /dev/ttyUSB0. For this reason, the Raspberry Pi must reboot if no valid port is detected.

Pi to Display Connection Specification

The Raspberry Pi and the LCD Display module connect using a series of cables linking the Raspberry Pi HDMI port to the Display’s RCA port. The RCA display was chosen for the cost/quality reasons. Alternative displays may be hot­swapped as necessary, so long as they can be registered by the Rasbian operating system and over the HDMI interface.

Xbee to Xbee Specification

Xbee modules are embedded solutions providing wireless endpoint connectivity to devices. These modules use the IEEE 802.15.4 networking protocol for fast point­to­multipoint or peer­to­peer networking.They are designed for high­throughput applications requiring low latency and predictable communication timing. Xbee modules are ideal for low­power, low­cost applications. Xbee units can be used for wireless communication with low power consumption. It communicates with well known UART interfaces and makes it easy to use. It is simple and straightforward if you only use 2 Xbee units for communication. Xbee units can communicate
up to 300ft and operate on 3.3 volts @ 50 milliamps. The board contains 6 ten­bit ADC input pins and 8 digital I/O pins. Xbee also allows for 128­bit encryption.

Figure 6/7, Xbee pin layout diagram

Xbee units consists of 20 pins. Eight digital I/O pins that allow the device to function with both input or output, set by software. Of these digital pins six can function to give the ADC input. One pin is designated for digital output only. Two pins, VCC and GND, provide power to the device. One pin also allows for voltage reference; while the other eight pins allow the Xbee to perform further functionality. Two pins allow for UART data in and UART data out. Two pins can function to allow PWM output. Three pins are set to either control sleep or reset, one of which allows for a sleep indicator. And the final pin is reserved.

Xbee Communication Protocol

Communication between the LCU and MCU is through the Xbee interface. No explicit Xbee encoding is used. The commands are as follow: (MCU sending, LCU receiving) open (LCU sending, MCU receiving) ackt batt Where is the lockerId of the designated locker, and is the battery level of the locker that wishes to update it’s recorded battery level in the database. All data sent is automatically encrypted by the Xbees.

USB Connection Specification

The keyboard and card reader are connected to the Pi using USB connection. The keyboard used is a qwerty keyboard normally used for desktops and laptops. The keyboard gives input of alphanumeric characters (ISU ID number and Password of the locker) to the Pi in order to be processed and then to send the appropriate information to open the respective locker.

Hardware Specifications

Locking Unit Specification

Servo Motor

The motor being used to control the locking and unlocking of the lock is a sub micro servo ­ GWS NARO HP BB. This servo has the capability to interface with PWM compatible devices and can hold any position from 0 to 180 degrees. The servo can apply 19.4 oz­in torque at 6VDC and can operate in the range of 4­6V. The servo also has a maximum current draw of 140+/­50mA at 6VDC and draws 15mA under static conditions.

Figure 8, Sub Micro Servo – GWS NARO HP BB

The I/O of the servo motor is connected to the ATMEGA328 via transistor. When the ATMEGA sends a signal to move the position of the servo, the increase in voltage causes the transistor to power the servo and move it to its desired location. When the servo does not receive a signal from the ATMEGA, it stays at its current location and operates under static current conditions. The servo is independently powered from the battery source in order to avoid current spikes and unnecessary power draw.


The lock being used is a Master Lock (1714) that is commonly used in athletic locker room lockers. The lock contains a 5­pin tumbler cylinder for supreme security and is key operated. The lock is spring loaded with its resting position in the locked position. The lock is controlled by the servo motor, which is connected to the lock via metal fasteners. When the servo moves, it pulls the lock into the unlocked position and then moves the lock back into the locked position once the unlocking time has expired. The spring loading capabilities of the lock make it so the lock can be in the locked position when the locker is open, then when one wants to close the locker, the lock is compressed to fit back in the locker and then expanded once fully in the locker.

Figure 9, Master Lock

Bi­LED (160­1057­ND)

A bi­colored (red/green) LED is used to provide user feedback of the status of the locker. A green light indicates that the locker has been unlocked. A red light indicates that the battery in the locker needs to be replaced. The LED is 5mm and operates on a 5V power source from the ATMEGA328.

Figure 10, Bi-LED

ATMEGA328 Microcontroller Specification

The ATMEGA328 is a microcontroller chip produced by Atmel. It is an 8­bit microcontroller that has 32KB of flash memory, 1KB of EEPROM, and 2KB of internal SRAM. The ATMEGA328 has 28 pins. It has 14 digital I/O pins, of which 6 can be used as PWM outputs and 6 analog input pins. These I/O pins account for 20 of the pins.

Source: Wi­Fi Connected Locker Access System

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