Program Control

Learning goals

• evaluate a solution for an industrial control problem and explain the relevance of programmable systems for these problems

• visualize a program using flowchart

• apply program control syntax (to implement program)

Problem

Fig. 2 25 Oct. 1969 - Commander of the Apollo 12 lunar landing mission, sits in the cockpit of a Lunar Landing Training Vehicle (LLTV) during a lunar simulation flight at Ellington Air Force Base.
Public domain. By NASA Johnson Space Center. Source: Wikimedia Commons

Various control systems

Mechanical ⚙️

Fig. 3 Steam engine using a centrifugal governor
CC BY-SA 3.0. By Panther. Source: Wikimedia Commons

Electronic 💻

Fig. 4 A chip on an Arduino board
Public domain. By DustyDingo. Source: Wikimedia Commons

Manual 🤹🏼

Fig. 5
CC BY 2.0. By Vernon Chan. Source: Wikimedia Commons

Table 1 Comparison of three control methods

Type	Pro 👍	Con 👎
Mechanical ⚙️	simple, reliable	bulky, complex systems not feasible
Electronic 💻	flexibility through programmability (computers), small	complex, reliability
Manual 🤹	very flexible, can cope with an unknown environment	costly, unreliable for repetitive tasks

Regardless of the method, we use electronics to connect all systems together

Exercise 2

As an engineer in the R&D department of the space agency you are designing the following subsystems of a lunar lander:

1. a sensor for pointing the antenna to the world 📡

2. subsystem for traveling from space to moon’s proximity

3. subsystem for landing on the moon 🛬

For these scenarios:

1. pick one control method

2. explain with an example how electronics (and computers) can help in this scenario

Steps:

1. ~1 min individually

2. ~2 min compare with your partner

3. Deliverable: Write down your result and keywords for explanation

Assumption: We use a programmable electronic system to solve our problem.

Mission: Safe landing

Fig. 6 Lunar lander trying to land

Problems:

• limited fuel 🌡️

• crash if high speed 💥

How do we control ❓

Flowcharts

Warning

We are repetitively running the program, i.e., if we are at the bottom, we come back to the beginning.

Exercise 3

Draw a flowchart for the following program

• if the altitude is higher than 100

  • the thruster must be off.

• if the altitude is lower than or equal 100

  • turn on the thruster

• if the altitude lower than or equal 0 (landing)

  • the thruster must be off.

Steps:

1. ~2 min individually

2. ~1 min compare with your partner

Program control syntax

General:

if (question1) {
  action1;
} else if (question2) {
  action2;
} else {
  action3;
}

Question examples:

• is the time 1?

  • time == 1

• is the temperature lower or equal 20?

  • temperature <= 20

Action examples:

• set the speed to 10

  • speed = 10

In words:

• if temperature is greater than 30 then activate air_conditioner

• else if temperature greater than 25 activate ventilator

• else turn everything off.

In code:

if (temperature > 30) {
  air_conditioner = 1;
} else if (temperature > 25) {
  ventilator = 1;
} else {
  air_conditioner = 0;
  ventilator = 0;
}

Exercise 4

Write code for landing using the following flowchart

using the following independent lines:

} else {
} else if (altitude > 0) {
if (altitude > 0) {
thruster = 1;
thruster = 0;
thruster = 0;
}

Steps:

1. Work ~2 min individually. The program automatically tests your code.

2. Compare your result with your neighbor and help them.

Appendix

In a programmable computer, program is programmed into the memory and executed by the computer.