# 0.2 3. traffic light station

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## Introduction

Without Traffic lights, most of you wouldn’t be here today. Such simple little things, but if they break, chaos erupts. You’ve started to make a name for yourself as a hot-shot programmer and the Traffic Department wants to put some of your skills to use solving Cape Town’s traffic problems for the 2010 soccer world cup.

## Task 1 - flashing red when down

When the traffic lights fail, traffic must still flow. Have you ever seen traffic lights flashing red? If something goes wrong in the control system, real traffic lights try to tell all the cars that something is wrong and that the intersection now functions as a stop street. They do that by flashing the red light continuously. Try writing a program to flash the red light once.

## Task 2 - flashing red three times

Flashing the red light once is good, but it’s not enough! Let’s flash the red light on and off three times.

## Task 3 - flashing red continuously

Can you make it flash forever without taking forever to write the program?

## Task 4 - normal sequence of lights

Ok, so the backup system works. Can you write the normal green, orange, red cycle?

## Task 5 - pedestrian crossing

A little further down the road is a different traffic light, and this one is for pedestrians. Can you write a program to let a pedestrian cross when they press the button? The light should remain green. When a pedestrian presses the button it should turn orange and then red to allow the pedestrian to cross. After that it should turn back to green and be ready for the next pedestrian.

HINT: Use 'Wait for' block to wait for a button to be pressed

## Task 6 - wait for more pedestrians

Pedestrians have been crossing the road in drips and drabs, slowing the traffic down unnecessarily. Can you write a program that only changes the light when three pedestrians have pressed the button?

HINT: Use the “Pulse Counter” The Pulse Counter works the same as the Wait button, except that it waits until it has been pressed the set amount of times before it allows the program to continue.

## Task 7 - real-time feedback

This solution helps to reduce the traffic delays, but the pedestrians quickly notice that if they keep on pressing the button the light changes without having to wait for another pedestrian. Can you change the program so that the light is always green and only red whenever the button is pressed in?

HINT: Use the “Digital Branch” to make a decision

## Task 8 - flashing a precise number of times

Remember how we were able to make the red light flash once, thrice or for ever. Can you make it flash very quickly for thirty times without switching the light on and off thirty times? What if we want to make it flash 1000 times? There must be an easier way than using the on and off command 1000 times? Write a program that shows a green light and when the button is pressed flashes the red light very quickly for thirty times before turning green again.

HINT: Use the “Counter Loop”.

## Task 9 - sub programs

Task 1. Often we will find tasks that we need to repeat. For example we might want to flash the red light thirty times in different parts of our program. Instead of re-writing that part using the counter loop every time we need it, we can create our own block or sub-program to do that. Then our program from Task 8. will look much simpler. Then whenever and as often as we need to we can use this sub-program to flash the red light thirty times. We can put anything we want in a sub-program and it helps us to simplify our programs. Turn your counter loop from Task 8 into a sub-program.

## Task 10 - combining the pieces

Now use all the tools you have learnt in the previous tasks and write a program which runs the regular traffic light sequence. When a pedestrian presses the button the lights need to switch to red and quickly flash thirty times to allow time for the pedestrian to cross before resuming the regular sequence.

## Bonus tasks

The Traffic Department is well pleased with your efforts. Someone asks whether it is possible to adjust the brightness of the traffic lights - he believes it should only shine at 60% instead of 100% brightness. Can you do that?

#### Questions & Answers

what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Introduction to visual programming with robo pro. OpenStax CNX. Jan 27, 2011 Download for free at http://cnx.org/content/col11270/1.1
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