Analysis of identification technologies and an
automatic lock for school lockers
David Marn
Abstract The main objective of the project was the improvement of identification systems in schools, and to find a solution to a specified problem with lockers. The goal has been reached by designing a new locker that is extremely easy to use and comes with an instant unlock mechanism. The designed locker is an improvement from the versions of locks that are currently used while still retaining the low price. The lock, designed for school lockers, is assembled using three modules: the access control module, electro-mechanical module and the power supply module. Because of the modular structure, it is possible to upgrade certain modules when better technologies become available, while leaving the other modules intact. If a lock would become defective for any reason, only the defective module would have to be replaced and the lock would function, which massively reduces the maintaining costs. The iButton could become the universal identification medium in high schools, as examples of its usage includes: granting access to school’s events as a ticket, ordering food in the school cafeteria, noting student’s presence at lessons and finally, unlocking their lockers. The iButton has the potential to be upgraded in the future, when more uses for it will be developed.
1
Introduction
Many public high schools have very limited government funding and have to resort to low quality outdated technology. One example of this outdated technology are the school lockers, which affect the quality of the school in the students' eyes. That is why economically-efficient solutions were sought in this project.
The main objective of the project is the improvement of identification systems in schools, and to find a solution to a specified problem with lockers. The criteria for the new locker includes the improvement of current locks with regard to simplicity, time consumtion and human factor. Another goal is to implement a new, universal identification technology, which will eventually replace all other mediums of identification, making our lives easier.
2
Outlining the problem
Those students in Slovene high schools who even have lockers in their schools are
mostly stuck with using combination locks. This technology is robust, but heavily
outdated, as the first such lock was invented by Andrew Elliot Rae in 1978.
Electronic school lockers do exist already, but they do not offer cost effectiveness
nor can their key be integrated with other systems, such as ordering the food at
school cafeteria, granting access to school’s events or installing readers into
classrooms, where it would take attendance. The current commercially available
electronic locks more than double the cost of the locker itself
1. Thus, schools must
resort to outdated combination locks.
First, current lock systems have to be analyzed, their disadvantages and
advantages recognized and the further development plan has to be drafted based on
these findings.
2.1
Time efficiency
The technology used in the combination lock is not aided by electronic components,
which results in relatively high time consumption in unlocking the lock. According
to an experiment, it takes always more than five seconds to unlock. In the
experiment, various students were asked to open their locker and the required time
was measured. Around 20 per cent of the sampled population entered the wrong
combination on the first try, which points to the high level of human factor and the
mistake added significantly to the result. It is true, on the other hand, that such high
percentage may be due to other reasons, such as stress caused by the experiment.
Even if we account for these errors, the human factor still exists in negligible
amounts. My findings have shown that pupils need 7.8 seconds on average to unlock
the locker at once.
This means that the pupils who will unlock their locker 9 times a day (a realistic
assumption based on the observation of the pupils, who generally unlock the locker
between each break and upon entering and before leaving the school) will spend
more than a minute of their time per day just for unlocking the locker. Furthermore,
because different technologies (such as RFID) are used for different tasks in the
same school, more ID tags are needed than necessary. With a unified system, only
one ID tag would be necessary and the time needed for authorization would
decrease.
2.2
Complexity
The design of the combination lock is space friendly due to low security level. The combination, which unlocks the lock, usually consists of three numbers, but only the first two numbers are required in order to get the right combination (because of the spinning mechanism, which allows you to try all the possible digits sequentially). This renders the third number useless and strongly decreases the number of combinations needed for a brute-force attack.
The second major weakness is that these locks are not secure due to the tolerance that allows you to unlock the lock if you were close enough (typically, 1 number on each side) to the correct number.
A simple mathematical calculation can show that these weaknesses reduce the time required for a brute attack of the combination lock by 99.8% (The calculation is in the appendix) compared to the theoretical time required for a 60 digit lock.
1 According to SchoolLockers (www.schoollockers.com), the price for an electronic lock is 61€, whereas
2.3
Human factor
It should not be forgotten that the students will be operating these locks, so the obvious human factor problem arises as they can miss the correct number and because of the cyclical unlocking mechanism, which is used by the combination lock, they have to start over and the resetting process for the mechanical lock lasts longer. The human factor is almost entirely eliminated when an electronically based lock is used as the human factor can only affects the process of reading the ID tag, which generally has to be scanned by a reader.
3
Criteria for the solution
Once the problems were outlined, the criteria which the final prototype should fulfill could be defined further. These criteria will be used for an informed judgment when comparing the pros and cons of different technologies to find the best possible solution. The time consumption is a very important factor, as it represents the greatest improvement from the current combination lock. It is important to use electronic parts as that reduces the human factor, which in part enables the maximum time-efficiency.
The time spent unlocking the lock is an essential part of the project, and as such it should be made quick as possible. The use of electronic components will be introduced as they offer almost instant identification and unlocking,and students will be able to spend more time in lessons or preparing for the lessons.
The technical functions must remain intact while using large quantities of locking units and ID tags in a small area. Some technologies are known to cause interference with wireless communication. This limits the number of locks per unit volume. A scenario in which the same ID-tag would be near two readers could result in resistance of the tag to its proprietary reader. Therefore technologies based on wireless communication are best to be avoided as they do not offer the best possible cooperation.
4
Overview of available electric identification technologies
The technologies that suit the criteria had to be identified, analyzed, tested if necessary, and the most suitable one had to be chosen. The information required for an informed judgment included the technology used, mass reproduction, energy consumption and cost efficiency.
4.1
iButton
The iButton is a computer chip enclosed in a steel can manufactured by Maxim. The chip contains a unique id, which can be used for identification purposes. A wide variety of iButtons exist, some contain sensors for measuring temperature, some contain microprocessors, but as these extra functions cost more, a basic iButton
should suffice for this project. The energy required for reading and writing is drawn from the reader/writer. The iButtons itself as well as the readers are very affordable.
4.2
RFID
Radio-frequency identification technology uses radio waves to exchange data between a reader and a tag. Unfortunately, such systems are designed for environments where only few readers are needed. The price of a single reader is too high to implement an individual reader for each lock. It is possible, on the other hand, to implement a reader for more lockers (such as a set of 20), but this would not satisfy the time criterion.
4.3
BAR code
Bar code scanners emit optical rays of visible light to read the BAR tags that are segments of lines of various-width. Although the tags are very cheap, they are an unacceptable solution for schools because of the requirement of large amounts of scanners, and because the scanning angle, scanning speed and poor contrast affect the identification process. Also, the BAR code readers were not meant to be used in such a way so the final price is quite expensive making barcodes a popular choice only when the ratio between ID-tags and readers is high (such as in supermarkets).
4.4
Magnetic stripe
The magnetic stripe has a relatively low data density of the magnetic tape, thus the cards are large and require a lot of plastic to hold the stripe in place. The cards are relatively cheap, but readers cost a lot. The magnetic stripe card could be unified for one’s identification as a valid ID, credit card and in schools to unlock the lockers or to be used to order lunch in school cafeteria. Unfortunately, the price of the reader is too high for a single school locker and the magnetic stripes are vulnerable to magnetic fields, which are known to damage or delete data on the card.
4.5
Chip card
The chip card is used where a high level of security is required, such as in SIM cards. Such cards are more expensive due to the manufacturing process, which in combination with the price of the reader makes it an uneconomical option.
5
Prototype design
The prototype of the locker was segmented into three modules: access control module, which defines the identification process, the electro-mechanical part, which opens the locker once the identity has been confirmed, and the power supply of the locker.
A single school locker consists of the access control module and the electro-mechanical part. A set of lockers consists of several single lockers, connected to a
single power supply module. The whole locker infrastructure consists of several sets of lockers and a master ID tag, which unlocks every locker.
5.1
Access control module
In this subchapter, some identification technologies will be compared in order to find the most suitable identification technology. A cross-comparison in table 1 has been constructed for a better overview of different technologies. The parameters are the use of electronic components (which results in the shortest possible time), the price of the ID tag as well as the price of the reader (wh ich influences the choice because of possible mass-production). Please note that the price of electro-mechanical module stays the same regardless of the identification technology used. The price is around 9€ (see table 1).
Table 1 Comparison of the prices of identification tehcnologies Identification
technology RFID iButton BAR code Stripe Card Magnetic Chip Card Combination lock Tag price 0.15 € 1 0.98 € 3 0.007€ 4 0.21€ 6 12.20€ 9 No tag Reader price 17.50 € 2 3.32 € 3 17.00 € 5 14.00 € 7 1.66 €10 20.00 €12 Total price 17.65 € 4.30 € 17.01 € 14.21 € 13.86 € 20.00 € 1 http://www.rfidjournal.com/faq/ 2 http://www.priority1design.com.au/shopfront/index.php?main_page=product_info&cPath=1&products_id=5 3 http://www.maximintegrated.com/ 4 http://www.barcodesinc.com/zebra/labels.htm 5 http://www.amazon.com/Contact-hand-held-Barcode-Scanner-Reader/dp/tech-data/B003OUTYBE 6 http://www.evolution-1.com/magnetic_stripe.htm 7 http://www.amazon.com/Triple-Track-Magnetic-Stripe-Reader/dp/B004IATGGM 8 http://www.smartcardsource.com/smartcardprices.html 9 http://www.hidglobal.com/main/omnikey-readers/3021-usb.html 10 http://www.masterlock.com/products/product_details/1690MD
The iButton fulfills all the criteria and a probe iButton reader will be installed into the locker. It will be connected with a circuit within the lock, which will control the mechanical module.
Already existing circuits have been found via the Internet. They are a good base
for further development and can be easily modified. Leonid Ridiko and Victor
Lapitskiy have constructed a similar lock circuit, which has been selected as a base
for the new circuit. The improvements to the existing lock circuit were necessary
because the existing circuit is not cost effective. In the end, a new, improved version
of the existing circuit will be created to drive the mechanical part of the lock.
5.2
Electro-mechanical module
The second module of the locker forms the mechanical part of the locker. Granted
access by the authorization module has to be converted into mechanical motion that
opens the locker.
First, the existing solution was analyzed. A strong pull of the combination lock in
one direction pulls the deadbolt into the lock, thus allowing the students to open the
locker. This indicates that a lot of kinetic energy is required for unlocking, which is
not a valid solution when using electricity as the power source. Thus, a new design
has to be found for the lockers.
The electro-mechanical part has to be energy-efficient, yet offer secure locking.
Because the door will be locked most of the time, the electro-mechanical module
must consume zero electricity while it is locked and only a fraction compared to the
existing solution while unlocking the lock. Because of the low energy consumption,
more lockers can be connected to a single voltage transformer, thus reducing the
costs.
A solenoid is an example of the electro-mechanical part, but it would only unlock
the door, not open it. In this case, a separate system must be installed to
automatically detect that the door is unlocked and immediately open it. It is best to
use kinetic energy whenever it will have no particular effect on the criteria of the
lock. Of that, a spring is a good example. When a spring is installed into the locker,
it will spring when the students close the door, preparing it for future use.
The final decision on the unlocking mechanism was made according to the
parameters regarding availability and low energy consumption. When the
availability is good, shipping costs as well as the price of the product itself is low.
The solenoid is a better option because it fulfills all the critearia.
5.3
Power supply module
The existing circuit scheme by Ridiko and Lapitskiy already includes transformation
from the main electricity voltage to the desired voltage of 14V. An array of batteries
could be used, but they are not environmentally friendly from the ecological point of
view. Also, it is not practical because the batteries have to be checked on regular
basis. That is why a transformer from the main voltage will be used. To reduce the
cost, a single transformer will be used for a set of lockers.
6
Prototype review
When a student wants to open his or her locker, they have to form a contact between
their key (in this case the iButton) and the probe reader, which will be the only
visible thing outside the locker. Then, the circuit within the locker will compare the
ID from the tag with the ID stored in the memory module of the circuit. If they
match, the circuit will unlock the locker.
If a student has lost his or her key, the locker can be unlocked using a master key
held by the school’s caretaker or similar authority, and later reprogrammed for a new
slave key. The access control module allows the usage of one master key, which
authorizes programming mode and multiple slave keys that cannot program the lock.
The programming of the circuit is very easy, as user-friendliness has to be taken into
account.
The lockers will be arranged in modules of
x
lockers, and each module will be
powered by a separate voltage transformer. The number of lockers in a single
module varies from school to school, as the place available and the maximum
number of lockers, which could be powered by a single transformer, have to be taken
into account. The scenario of a defect transformer or a general power failure must
also be taken into consideration. In that case, the lockers will remain locked until the
power is restored. Unfortunately, during the time of the failure, the lockers will not
function. However, it is possible to restore the power using batteries.
The complete pricing can be seen from table 2.
Table 2 Prices of the parts of the prototype.
Part Price
Microprocessor 1,50 € Transistors, resistors, diodes 2.00 € LED display 2.00 € Memory chip 0.50 € iButton 1.70 € Solenoid 3.00 € Spring 0.20 € Total 10.90 €
7
Conclusion
The main objective of the project was to improve the identification systems in schools, and to find a solution to a specified problem with lockers. The goal has been reached as a new locker has been designed. The new locker design offers instant unlocking of the locker, and is extremely easy to use without the interference of the human factor.
The new locker is an extensive improvement to the different locks that are currently used while still retaining the low price. The lock, designed to be used in school lockers, is assembled using three modules: the access control module, electro-mechanical module and the power supply module. Because of the modular structure, it is possible to upgrade certain modules when better technologies become available, while leaving the other modules intact. If a lock would become defective for any reason, only the defective module would have to be replaced and the lock would function, which massively reduces the maintaining costs.
The iButton could become the universal identification medium in high schools, as examples of its usage include: granting access to the school’s events as a ticket, ordering food in the school cafeteria, noting student’s presence at lessons and finally, unlocking their lockers. The iButton has the potential to be upgraded in the future, when more usages for it will be developed.
