11. Programming (5)

Question 1

Why do we need to use the serial interface?

Answer 1

To get things started and to print data

Question 2

Function for setting things up using the serial port?

Answer 2

Serial.begin()

Question 3

Function for printing using the serial port?

Answer 3

Serial.print()

Question 4

Function for printing and starting a new line using the serial port?

Answer 4

Serial.println()

Question 5

How can you debug using the serial port?

Answer 5

By printing values of variables at certain locations you can trace what is going wrong.

Question 6

If there is nothing wrong with your program what else could be wrong?

Answer 6

There could be something wrong with the hardware: maybe how it is connected/ connected to the wrong pin. If not, then look elsewhere, what happens next in your program?

Question 7

What are the advantages and disadvantage of debugging using print statements?

Answer 7

Disadvantage: not very elegant
Advantages: simple and often very effective

Question 8

What must you remember to do after using print statements for debugging?

Answer 8

Delete all the print statements afterwards

Question 9

What is another option for debugging?

Answer 9

More advanced debuggers exist, these let you step through your code line by line, to see what is happening at each step.

Question 10

What is an example of an advanced debugger?

Answer 10

Uno Ardu Sim, a free arduino uno simulator

Question 11

How can the monitor be used for a more useful application?

Answer 11

Can be used as a simple datalogger

Question 12

What is a datalogger?

Answer 12

A system that collects information and lets us download it to a computer when we are ready

Question 13

What does the hardware setup look like to investigate switch bouncing?

Answer 13

DRAW

Question 14

What happens when the pushbutton is pressed?

Answer 14

It acts as an analogue input at the upper pin and as a digital input at the lower pin

Question 15

Should we use the built in pull up resistor here? What value should the resistor roughly have?

Answer 15

R should be low (about 2kOhms) since this is the input impedance to the ADC. For this reason we do not use the built in pull up resistor.

Question 16

What function can be used to set the number of bits in an analogue input pin?

Answer 16

analogReadResolution()

Question 17

How is the analogue data read?

Answer 17

Using the analogRead() function

Question 18

For a 12 bit analogue reading what value would the analogue input signal return for 0V and 3.3v?

Answer 18

0V - reading of 0

3.3V - reading of 4095 (2^(12) - 1)

Question 19

If we want to use the mc as a data logger, what is the problem with just reading the data, writing it to the serial port and then repeating?

Answer 19

It succeeds in reading the data and passing it to a computer BUT:

1. the mc needs to be attached to the computer at all times. You may want it to be stand alone.
2. This is REALLY SLOW. The Serial.println() command takes a long time. E.g. with a max baud rate of 115200 it takes about 100microseconds to transmit one byte, and we need at least 2 bytes for a 12bit number. For comparison the ADC conversion takes around 1microsecond.

Question 20

With the SAM3X how much memory do we have to store data? How many 4byte readings do we have the potential to store then?

Answer 20

Have 96kBytes of SRAM…. 24000 readings.

Question 21

How can we store a large amount of readings/numbers?

Answer 21

In an array

Question 22

How to create an array of 1000 integers?

Answer 22

int readings[1000];

Question 23

What is the start index and final index number for this array?

Answer 23

reading[0] is the first reading and reading[999] is the last reading.

Question 24

Why cant we use the variable reading[1000] for this array?

Answer 24

The compiler wont give an error but the program would be liable to crash in unexpected and horrible ways. That is because this refers to a chunk of memory that the program may be using for something else.

Question 25

What is the error for trying to use an index outside of an array?

Answer 25

“array index out of bounds”

Question 26

What is the loop for reading in all the values from an analogue signal using an array of 1000 integers ?

Answer 26

int readings[1000];

for(int index=0; index

Question 27

In the previous examples where the array was declared as int readings[1000]; what do we call the number 1000 and is this a good thing?

Answer 27

1000 would be known as a ‘magic number’ it is a bad thing but not as bad as an array index out of bounds error.

Question 28

How do we get rid of the magic number 1000 that is the array size?

Answer 28

using the # define statement, known as a preprocessor directive. E.g.
#define DATAPOINTS 1000;

Question 29

What would the previous code for reading in the values now become?

Answer 29

#define DATAPOINTS 1000;
int reading[DATAPOINTS];
for(int index=0; index

Question 30

Why is this code with the define statement better?

Answer 30

Because now if we wanted to change (eg double) the number of data points all we have to do is change the first line.

Question 31

What is DATAPOINTS here called? and does it have to be in capitals?

Answer 31

It is called an identifier and it is in capitals because of tradition, not because it is essential.

Question 32

What is good about having it in capitals?

Answer 32

It is useful because it makes the constants in the program stand out.

Question 33

Could we use: const int DATAPOINTS = 1000; instead of the #define statement?

Answer 33

NO, cant use constants for an array size

Question 34

How would we then transmit the data readings to a computer?

Answer 34

Using a loop:

for(int index=0; index

Question 35

How could we save the time of capture for the data?

Answer 35

using the micros() function, which returns the number of microseconds since the sam3X was powered up.