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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.

Programming tasks

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

show that the set of all natural number form semi group under the composition of addition
Nikhil Reply
what is the meaning
Dominic
explain and give four Example hyperbolic function
Lukman Reply
_3_2_1
felecia
⅗ ⅔½
felecia
_½+⅔-¾
felecia
The denominator of a certain fraction is 9 more than the numerator. If 6 is added to both terms of the fraction, the value of the fraction becomes 2/3. Find the original fraction. 2. The sum of the least and greatest of 3 consecutive integers is 60. What are the valu
SABAL Reply
1. x + 6 2 -------------- = _ x + 9 + 6 3 x + 6 3 ----------- x -- (cross multiply) x + 15 2 3(x + 6) = 2(x + 15) 3x + 18 = 2x + 30 (-2x from both) x + 18 = 30 (-18 from both) x = 12 Test: 12 + 6 18 2 -------------- = --- = --- 12 + 9 + 6 27 3
Pawel
2. (x) + (x + 2) = 60 2x + 2 = 60 2x = 58 x = 29 29, 30, & 31
Pawel
ok
Ifeanyi
on number 2 question How did you got 2x +2
Ifeanyi
combine like terms. x + x + 2 is same as 2x + 2
Pawel
x*x=2
felecia
2+2x=
felecia
×/×+9+6/1
Debbie
Q2 x+(x+2)+(x+4)=60 3x+6=60 3x+6-6=60-6 3x=54 3x/3=54/3 x=18 :. The numbers are 18,20 and 22
Naagmenkoma
Mark and Don are planning to sell each of their marble collections at a garage sale. If Don has 1 more than 3 times the number of marbles Mark has, how many does each boy have to sell if the total number of marbles is 113?
mariel Reply
Mark = x,. Don = 3x + 1 x + 3x + 1 = 113 4x = 112, x = 28 Mark = 28, Don = 85, 28 + 85 = 113
Pawel
how do I set up the problem?
Harshika Reply
what is a solution set?
Harshika
find the subring of gaussian integers?
Rofiqul
hello, I am happy to help!
Shirley Reply
please can go further on polynomials quadratic
Abdullahi
hi mam
Mark
I need quadratic equation link to Alpa Beta
Abdullahi Reply
find the value of 2x=32
Felix Reply
divide by 2 on each side of the equal sign to solve for x
corri
X=16
Michael
Want to review on complex number 1.What are complex number 2.How to solve complex number problems.
Beyan
yes i wantt to review
Mark
16
Makan
x=16
Makan
use the y -intercept and slope to sketch the graph of the equation y=6x
Only Reply
how do we prove the quadratic formular
Seidu Reply
please help me prove quadratic formula
Darius
hello, if you have a question about Algebra 2. I may be able to help. I am an Algebra 2 Teacher
Shirley Reply
thank you help me with how to prove the quadratic equation
Seidu
may God blessed u for that. Please I want u to help me in sets.
Opoku
what is math number
Tric Reply
4
Trista
x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
Sidiki Reply
can you teacch how to solve that🙏
Mark
Solve for the first variable in one of the equations, then substitute the result into the other equation. Point For: (6111,4111,−411)(6111,4111,-411) Equation Form: x=6111,y=4111,z=−411x=6111,y=4111,z=-411
Brenna
(61/11,41/11,−4/11)
Brenna
x=61/11 y=41/11 z=−4/11 x=61/11 y=41/11 z=-4/11
Brenna
Need help solving this problem (2/7)^-2
Simone Reply
x+2y-z=7
Sidiki
what is the coefficient of -4×
Mehri Reply
-1
Shedrak
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Kimberly Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris 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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