Essay: Passenger counting system (draft)

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  • Subject area(s): Engineering essays
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  • Published: September 14, 2021*
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Opening/Mission Statement

The aim of the project is to improve the efficiency of train travel by indicating how full a carriage is, which speeds up the boarding and embarking of trains.


To maximise the seating and space usage of train carriages for the benefit of the train company.
To improve the comfort of train passengers by allowing them to locate a seat or space on the train carriage within a shorter period.
To reduce the time it takes to fill a carriage which is beneficial to train company and passengers.
A faster rate at which carriages are filled up makes the train company more efficient.
A faster rate at which carriages are filled up reduces the waiting time at a stop that is not the final destination. It would make the train service more reliable for passengers by reducing delays which could arise from a longer loading time than expected.

Time Management And The Gantt Chart

Background Research

Train Specifications

Before the design method could begin, the specifications of the train must be known. A research was carried out to find out the train specifications. The train specification used is the S7 Stock.



Number of Carriages: 7

Door Width: 1610 mm

Door Height: n/a

Seating Capacity (Full seats): 256 (approximately 36 per train carriage)

Seating Capacity (Tip-up seats excluding wheelchair spaces): 44 (approximately 6 per carriage)

Wheelchair spaces: 4

Standing Capacity(5 customers per square metre): 778*

Standing Capacity(7 customers per square metre): 1112*

Total Passenger Capacity : 951

*figures exclude seating capacity


Transport For London Rolling Stock & What Do They Know

Transport For London – Rolling Stock


We came up with various ways to measure if there is space for more people on the train. The ways are:


The available space on a train carriage could be measured through weight. The S7 stock weighs 213.7 tonnes when empty. Assuming each carriage has identical weight, each carriage weighs 30.5 tonnes. The average weight of a man and woman in the UK respectively is 84.0kg and 69.0kg. The mean of the two averages is 76.5kg. At capacity, the train will have an additional weight approximately 73 tonnes. The amount of space is dependent on the amount of additional weight (with the maximum additional weight of 73 tonnes). The higher the additional weight the lower the vacant space for passengers to occupy.

Counting the number of people

The central part of the London Underground Train system is the sensor. The sensor will count the number of people in the carriage. The sensor will operate based on the number of people entering and exiting the train carriage. The sensor program is based on a maximum of two people going through the train doors.

We decided to count the passengers using sensors that will count the number of people entering and leaving the train. Below are possible situations for passengers entering and leaving the train door.

Practical activities involved in designing

A practical experiment on the different scenarios of people entering and leaving the train was conducted. The experiment raised the question of where to position the sensors on the train door. The conclusions of the practical experiments are;
Infrared sensors will be placed on the carriage doors of the trains and will send a signal to the Raspberry Pi whenever a passenger crosses through the door and breaks a beam from a sensor. The Raspberry Pi will evaluate the number of times each sensor was interrupted, as well as, assess the number of passengers that came in and out of the train. The change in the number of passengers is added to the total number of passengers on the train before it stopped. The programmed software will evaluate whether the carriage is full or not, and send a signal to the RGB LED (Red, Green, Blue Light-Emitting Diode) through the GPIO(General Purpose Input/Output) pins: output red if full, green otherwise and orange for somewhere in between. The RPi will send the output to the LCD via pins. The LED will display a more visual piece of information to the passenger. The RPi will also debug. The stretch challenge is for the Raspberry Pi to connect to a network on every station and display the number of passengers to users of such network using a mobile device with an app, or just a large display on the wall.


Design of the Casing

The Raspberry Pi 3 Model B, the Liquid Crystal Display and the LED are to be placed inside a case/box which is pre-made. The material used to make the box perspex and it is transparent. The box is a regular container, however, adequate appropriate holes have been drilled to the case to allow for screws, connectors, and outlets. The case is assembled from the six panels and it is joined together through glue.
A decision was made that wires will be run from the box to the sensor transmitter and receiver so that the unit itself can be placed by the door so people going in and out can be counted, but the raspberry pi and the display will be placed on the top of the train door.

Power will be supplied to the Raspberry Pi from an external output source supplying +5V and 2.5A (DC). This will deliver power to the Raspberry Pi through the power input connector at the bottom of the Raspberry Pi.

The LED will be placed inside the casing on the front panel of the box so it can be visible from the outside. The LED will assume various colors depending on the number of people in the train carriage. The LED will be programmed to do this. The LED is connected to the Raspberry Pi through a wire.

The LCD will be placed on the front panel of the case and it will be held in place through a screw. The display through a wire is connected to the Raspberry Pi.

The panels were cut with a laser cutter at the EES Workshop in December. RS PRO 250ml Liquid Acrylic Adhesive was used to assemble the panels.

Design Of The Door Frame

A model of the train door was designed to aid demonstration. The model was made from pinewood and chipboard base . A panel made of (insert name of material) was mounted at the top of the door frame for the case housing the Raspberry Pi, the LED and display to rest on.

After gathering information on the specifications of the S7 stock, we made a model of the train by reducing the specification using a ratio. The ratio of the model door frame:the real door is 1:4.375

Block Diagram

Circuit Diagram of Raspberry Pi

Program for the Sensors

The programming language chosen was Python. We chose python for the following reasons:

It is well-known.

It is easy to understand.

It is easy to program.

A program was written to detect whenever an object moved past two receivers, identify the direction of motion, and change a counter, which would be the number of people in the train, according to the direction of movement. Whenever a beam is broken, a variable will change to one. In the next loop, that variable changes to 0 and another one to 1, meaning that a beam has been broken in a previous loop. Whenever the other beam is broken, the system will identify that something has gone past both sensors, and identify the direction of motion, since the beam has been broken on that loop
14. Assembling the RPi


Outcome of the Practical Work


Below are the possible situations of people entering and leaving the carriage;

F1 , F2 and S1 are placed in the outside of the door.

When one man passes the door

First situation


First: F2, S1 triggered

Next: B2, S2 triggered


First: B2, S2 triggered

Next: F2, S1 triggered

SECOND Situation


First: F1, S1 triggered

Next: B1, S2 triggered


First: B1, S2 triggered

Next: F1, S2 triggered

THIRD Situation


First: S1 triggered

Next: S2 triggered


First: S2 Triggered

Next: S1 Triggered

When two men pass the door

Two men entering at same time

First: F1, F2, S1 triggered

Next: B1, B2, S2 triggered

Two men exiting at same time

First: B1, B2, S2 triggered

Next: F1, F2, S2 triggered

Left man exiting, while right one entering

First: B1, F2, S1, S2 triggered

Next: F1, B2, S1, S2 triggered

Left man entering, while right man exiting

First: F1, B2, S1, S2 triggered

Next: B1, F1, S1, S2 triggered




This information would be displayed by LED and LCD.

We could get the free space of a carriage in the number of people on the LCD, according to the formula:

The Total Quantity – The Number + The Number

Of People(125) Of People Getting In Of People Getting Out

LED represents the number of passengers staying in a carriage in different colours, with reference to;

0-31 people —— Green
32-94 people—- Yellow
95-125 people — Red

The information is presented on an app for mobile devices connected to the internet wirelessly.


Challenges Encountered


The receiver would initially remain low even when the light was directly shone on it. It did emit a signal after the beam was broken. Initially, a program was made with the Raspberry Pi to make the LED oscillate, but the frequency of oscillation was not continuous, given that the operating system of the RPI caused background interruption to the program running. It was also difficult to set the right oscillatory frequency – 38kHz using the program only.

The next day we investigated an alternative solution by using an ‘astable multivibrator’ to make the LED output oscillate between ON and OFF at a fixed frequency of 38kHz (carrier frequency of receiver). Using the appropriate components, the receiver would now be ‘on’ when the light was placed next to it. It was actually oscillating between high and low very rapidly that it seemed as though it was constant.

However, we needed to write the loop to pause the astable multivibrator to get a wider range of distance, however this would stop the remaining python code for running. So the sensor was switched on permanently, being high if the beam was interrupted and low otherwise.

Afterwards, the program was written. When the sensors were mounted, it was noticed the program was not running appropriately. Counting objects moving in as moving out, or not counting at all.






Bill Of Materials

Raspberry Pi Model 3B.

Raspberry Pi 16GB NOOBS Micro SD card.

Keyestudio PCF8591 AD/DA Functions Shield GPIO Expansion Board for Raspberry Pi.

Hrph 2PCS Digital 38KHz Infrared IR Sensor Transmitter Kit.

Adafruit APA102 5050 RGB LED with Integrated Driver Chip.

1.8inch LCD Display Module Kit General Screen 128×160 Pixels SPI interface.

Active HDMI to VGA Adapter with Audio, Benfei HDMI to VGA Converter Gold-Plated Cord

Total Cost: £163.20


LCD – Liquid Crystal Display
LED – Light Emitting Diode
RPi – Raspberry Pi
Electrosome [22/12/2018] -

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