Executive Summary

Need for this project:

This project stemmed from the problem of passengers being locked on board bus’s for an extended period of time. This is a direct result of bus drivers forgetting or neglecting to check every area on the bus before exiting and locking the bus. Due to the frightening nature, and the repercussions of these mistakes that may take place in civil court, it is the job of this team to design a system to insure that passengers are not locked on a bus purposely.

Actual Project Activities:

The team followed a scientific approach to this problem. Possible solutions were created and then either ruled out or ruled in by specific determining factors. These factors included: ability to be implemented, cost, applicability, feasibility, robustness, power consumption, and reliability. Upon choosing a solution, the team created a design to be implemented and then presented this idea to the client. Upon approval the team decided that there was a better way to design the system. The overall appearance of the new design was similar to that of the original. However, the new design would implement a theory of phase detection. Research went into the phase detection unit and the complex circuitry it required. Once there was understanding, parts were ordered and individual circuits built. These circuits and parts were all tested for integrity, and as smaller circuits were combined to make bigger circuits continuous testing was implemented.

Final Results:

What stemmed from the activities listed above was a hybrid system of two technologies used to detect passengers and larger items on a bus. The system consists of pressure sensors underneath the covers of the seats to detect weight on the seat above 10 lbs. And to cover the floor, optical emitters and receivers are used utilizing phase detection to detect anything blocking the path between the emitter and receiver. The phase detection unit allows a receiver to accept only the signal of the emitter it is told to accept. Thus, noise from surrounding emitters is being omitted. Although a finished system is not available, nearly all the circuitry is finished, except for a tune up of the phase detection with the testing to follow.

Follow On Work:

To complete this system the party involved will need to devise a method to distribute weight over the seat so that the pressure sensor will be able to sense the weight of a person or item anywhere on the seat. Also, implementation of the phase detection circuit into the receiver must be completed and tested. The team was able to make this unit work on occasion, however, a faulty breadboard has slowed the progress. A circuit must also be created to threshold the alarm according to outputs from the individual sensing units to be implemented on the bus. Output readings of when no one is present and the readings of when someone is present must be taken into consideration. Also, containment units for the receiver and emitter must be constructed to protect the circuits from being kicked or tampered with. A plexiglass was tested for the ability to pass infrared light, which was successful, so this is the recommendation of the team.

Acknowledgement

The senior design group, #Dec03-05, would like to acknowledge the client Heart of Iowa Regional Transportation Agency (HIRTA), located in Des Moines, Iowa. HIRTA is setting the criteria for this proposed project and will determine the future life of the end product. In addition to setting the criteria, the client is readily making available a bus for testing use. HIRTA may also supply additional financial aid if necessary to successfully produce an operational end product.

The team would also like to acknowledge Professor Clive Woods, who has supplied technical advice and mentoring throughout the entire project.

Problem Statement

The client has claimed that several times in the past year, a young passenger has fallen asleep on a bus and been left unaccompanied and therefore, was locked on the bus for an extended amount of time. Although the drivers are supposed to check the bus for any remaining passengers, the current events have given rise to a needed automatic detection system that would prevent these unfortunate occurrences. This system must function automatically without any driver initiation. The detection system must alarm the driver of any passengers remaining on the bus at the end of the route and it must react quickly enough to attract the driver, as well as the ability to detect non-human items that may have been left on the bus by previous passengers. The system must be able to be used on various bus types used by several transportation agencies, in addition to being robust, self-diagnostic, and failsafe, while keeping moderate in cost. It is also suggested that the application of the system be investigated on other mass transportation systems.

The detection system will operate automatically without driver initiation and will automatically alarm the driver of any passengers or items remaining on the bus. A range from 14 to 50 pressure sensitive sensors will be used to detect an on-board passenger that is remaining in a seat. Optoelectronics will be implemented along the floor and under the seats to detect a passenger that may have fallen asleep on the floor. Light emitting diodes (LED’s) will be used, as the light source, and photodiodes will be used, as a receiver. Each row of seats will have its own emitter and receiver pair along the floor. The system will be powered by the bus’s 12-volt battery and connected through the bus’s fuse box. An analog alarm system will be installed to alert the driver. If the alarm is set off it will be manually turned off. Otherwise the system will shut itself off after 30 seconds.

Operating Environment

The end product must function on a transient bus; therefore, it will be subject to vibrations from the bus’s engine and roadways traveled. The system must withstand environmental elements such as dust, dirt, and moisture. The system must also be able to function at normal temperatures found throughout the year in the central United States. It must also be able to withstand any pressure given off by a passenger.

Intended User(s)

The user(s) of this product is intended to be a male or female adult, who has acquired a commercial driver’s license. User(s) will not be discriminated against on the basis of sex, ethnic background, physical size, or disability, as long as he or she is able to operate the commercial vehicle according to the laws of the state.

Intended Use(s)

The detection system will operate automatically at the end of the bus route to detect remaining passengers and possible items that have been left aboard. If there is a passenger remaining on the bus, the driver will be alarmed of the situation before he or she has fully exited the bus.

Assumptions

The following is a list of assumptions:

  • Will be used on a transient bus.
  • The buses occupancy ranges from fifteen to seventy-five passengers.
  • The system must detect between one and seventy-five passengers.
  • The system is off while the bus is running.
  • The system starts when the bus is shut off.
  • After completing the detection process the system turns off or alerts the driver automatically. The driver then hits a button to reset the system, it will then give a predetermined amount of time for the driver to remove the passenger or object then run through the detection process again. This process runs until the alarm is not triggered
  • The system must be versatile and compatible with other buses and transient systems.
  • Pressure sensors cover all seats.
  • The LED’s attenuation is eight to ten feet.
  • Receiver sensitive to infrared light emitted by LED only.

Limitations

The following is a list of limitations:

  • Cost of production not to exceed two hundred fifty dollars.
  • Power for the system must come from a 12-volt battery.
  • Structure of the bus will determine paths of detection due to the blocking and reflection of signals off of steps, guard rails, and the base of seats..
  • Response time must be under five seconds.
  • System must be able to withstand a maximum weight of three hundred fifty lbs. applied to the seat sensor.
  • System must not trigger below ten lbs. of weight applied to the seat sensor.
  • Must be self-operational.
  • System able to withstand operating environment.
  • System must only respond to the spectrum of the LED.

Expected End Product and Other Deliverables

The expected end product will be a fully functional passenger detection system for public buses. The system will include pressure sensitive sensors installed in the seats and optoelectronics along the floor. An automatic alarm will inform the driver of any passengers or items remaining on the bus. The system will also include an initiation device that will start the detection process. The majority of the end product will not be visible to the passenger or driver. The detection system will blend in with the cosmetics of the bus and will not affect the layout of the bus itself. There will be an analog alarm that will be located near or on the dashboard of the bus that will not be restrictive or distracting to the bus driver.

Design requirements

  • Self-automated – Develop a solution that starts up and shuts off without the interaction of the bus driver.
  • Energy efficient – Develop a solution that ideally requires no other power source besides the bus battery.
  • Thorough visibility – Develop a solution that can thoroughly check every part of the bus for passenger(s) or item(s).
  • Speedy detection – Develop a solution that alerts the driver of passenger(s) or item(s) before he/she is off the bus.
  • Fail-safe – Develop a solution that will always gets the drivers attention as to alert of onboard passenger(s) or item(s).

Design constraints

The following is a list of constraints on the passenger detection system that the system must overcome to be successful in its operation.

  • Placement position – System should not be restrictive, distracting, or discomforting to the driver and passengers.
  • Small size – System should not interfere with normal bus operations.
  • Fail-safe detection – System should never neglect to alert if a passenger is present when the bus is shut off.
  • Low power consumption – Power from the system must come only from the bus’s 12-volt battery, thus minimal power must be used to prevent the system from draining the bus’s battery.
  • Response time – System will need to respond within 3-7 seconds of the bus being shut off.
  • Robust – System may be exposed to the elements and anything tracked on by passengers such as: rain, snow, mud, dust, and dirt.
  • Flexible – Design implementation must be supported for several bus designs.
  • Cost effective – If system cost is over $100, some type of funding must be provided.

Functional requirements

The following is a list of requirements the passenger detection system must be capable of to be successful in its operation.

  • Passenger warning system – System will warn the bus driver of still onboard passenger(s) when the bus is shut off.
  • Item warning system – System will warn the bus driver of still onboard item(s), at least as large as a small purse, when the bus is shut off.
  • Automatic power-on and power-off – System will start automatically upon bus turning off and then shutdown when the bus is started.
  • Timer delay shutoff – System will stop detecting after a predetermined amount of time and shut off at that point. Since the driver has exited the bus, there is no need for the alarm at this point. This will also stop the system from draining power from the bus’s battery.

Technical approach considerations and results

Technology / Pros / Cons
Light sensitive resistors / - Cheap
- Easy to use / - Installation of many lights necessary
- Light pollution from sun makes
readings inaccurate
Pyrometers / - Pre fabricated
- Unaffected by bus
interior / - Expensive
- Not designed specifically for
temperatures as low as this system
contains
Ultra-sonic signature / - Few electronics or
sensors needed / - Hard to implement
- Very expensive
Pressure sensors / - Accurate and easy
to install
- Detects any pressure at all / - Overall cost per bus is relatively high
compared to budget
Optical counters / - Have one distinct
position to detect
- Inexpensive / - If a mother or father was carrying a
child onto the bus the counter would
only recognize them as one person.
Therefore it is not failsafe
Magnetic counters / - Have one distinct
position to detect / - Magnetic cards could be easily lost
which would result in an non-failsafe
solution.
Infrared LED (emitter) / - Economical
- Minute / - Lots of research needed
- Positioning is very crucial
Weight systems / - Simple procedure / - Accuracy
Analog alarm system / - Easy to install
- Low cost / - Sound level may be to high or low
Digital display system / - Displays
passenger location / - More complex to implement
- Driver may overlook display
Piezoelectric sensors / -Does not need a power supply / - Pressure may not be great enough to
trigger the electric field in quartz
Photodiode (detector) / - Economical
- Minute / - Lots of research needed
- Positioning is very crucial

Results: After researching each technology, it was found by the team that the problem would be better solved with a combination of two technologies, dividing the problem into two separate areas. The first area needing attention was the seating on the bus. It was decided that pressure sensors would be the best implementation for this area. The relatively cheap cost and easy implementation for the problem at hand made this technology an easy choice. The floor was the team’s secondary area of concern. It presented a harder task at hand due to the large area that needed to be covered. This ruled out pressure sensors due to the vast number of sensors that would need to be purchased. It was decided that the LED emitter/photo detector sensor combination would best cover this area for the team. Multiple LED emitters and photo detectors, which are quite cheap, gave the team a solution that could cover a large amount of the floor space with proper placement and design. These are the solutions presented to accomplish the sensing of passengers and/or items on the bus, in the most effective manner.

Detailed Design Description

For the design of this system the team broke off into two teams, the computer engineers were assigned to the seat detection and the electrical engineers were assigned to the floor assignment. The teams were chosen based off of knowledge in circuitry, and then the more talented team members in this area were assigned to the more involved circuits, which, to no surprise, was the floor optoelectronics.

The design of the floor detection unit was chosen to use optoelectronics due to its ability to cover large areas at a cheap price. The surface area of the floor alone ruled out pressure sensors. It would have cost thousands of dollars to implement a matt on the floor implementing these pressure sensors to cover the area that was needed to be monitored.

The design of the seat detection unit was chosen to use force sensitive resistors due to the fact that they were easier to implement, and had natural features for detecting any pressure on the seats, even just a touch. The optics installation is much more involved than that of the pressure sensors due to the fact that the optical receiver and emitter need to be aligned correctly. Therefore, each installation becomes a custom installation job meaning higher costs for installation. By choosing the pressure sensors, which are very easy to implement under the cover of a seat, it is the hope of the team that installation prices will be reduced. It was easy to note that either a person would have to be in contact with the floor, which allowed our optics to detect them, or they would have to be putting pressure on the seat to not touch the floor, which means our pressure sensors would detect them.

Next is a closer look at each unit of the passenger detection system.

Optical Technology:

The optics part of this design is one of the two main parts of the hybrid system. It is expected to be able to detect any lying bodies or left items on the floor in which the pressure sensors would have undoubtedly ignored.