Datalogging with the Arduino

30 seconds of temperature data recorded using the Arduino (over the serial port).

I wired a temperature sensor to my Arduino as part of the third project in the Arduino Projects Book. The project has the Arduino send the data to the serial port where the Arduino program (IDE) can show it. This data would be most useful to me, however, if it could be logged in a plain text file for data analysis. However, it’s a little annoying that there isn’t an easy way to save the data output by the Arduino.

So, I needed to use the terminal program “cat” to look at what was coming across the serial port. First I had to look up which port the Arduino was connected to in the Tools menu of the Arduino IDE: since I’m on a Mac, running OSX, this turned out to be something like /dev/cu.usbmodem411. (I could have looked this up by listing the contents of the /dev/ directory and then looking for anything connected to the usbmodem). To see the data I used:

> cat /dev/cu.usbmodem411

To actually save the data I directed the output of the cat command to the file data-log.txt:

> cat /dev/cu.usbmodem411 > data-log.txt

The contents of the file looked like this:

T25.68
6003,25.68
7504,25.68
Time (milliseconds), Temperature (deg. C) 
0,25.20
1501,25.68
3002,25.68
4502,25.68
6003,26.66
7504,28.12
9006,30.08
10335,32.03
11663,33.98
12992,35.45
14321,36.91
15650,38.38
16979,39.84
18309,41.31
19559,42.77
20810,43.75
22062,42.77
23313,41.31
24563,40.82
25815,39.36
27144,38.87
28473,37.89
29802,37.40
31131,36.91
32459,35.94
33788,35.45
35118,35.45
36447,34.96
37776,34.47
39105,33.98
40434,33.98
41763,33.50
43091,33.01
44421,33.01
45750,33.01
47079,32.52
48408,32.52
49737,32.52
51066,32.03
52396,31.54
53724,31.54

I’m not sure what’s the deal with the first three lines, but if you ignore them you see the column headers (Time and Temperature) and then the time (in milliseconds) and temperature data) in a nice comma delimited format.

The Arduino program (sketch) that produced this output was:

const int T_sensor_Pin = A0;
const float baselineTemp = 20.0;
const int outPin = 4;

void setup(){
  
  Serial.begin(9600);
  pinMode(outPin, OUTPUT);
  
  Serial.println("Time (milliseconds), Temperature (deg. C) ");

}

void loop(){
  int T_sensor_Val = analogRead(T_sensor_Pin);
  
  float T_sensor_Voltage = (T_sensor_Val * 5.0)/1024.0;
  
  float T = (T_sensor_Voltage - 0.5) * 100;
  float T_F = (T * 1.8) +32.0;
  
  Serial.print(millis());
  Serial.print(",");
  Serial.println(T); 

  delay(1500);
  
}

Alternative Methods of Saving Data

Python

Based on the same Arduino sketch, you can write a Python program to read the data. This method enables you to use the data directly with VPython for visualization.

First you need to install the pySerial library (pySerial). Then you can read the serial data using:

data-log.py

import serial

ser = serial.Serial('/dev/cu.usbmodem411', 9600)

while True:
    print ser.readline()

CoolTerm

You can also use CoolTerm to save the serial data (see directions on how).

An SD Card

Another alternative, is to get a shield that can hold an SD card (SparkFun and Adafruit have ones for less than $20) and write to that.

3d Printing at School

One of the key ideas behind the design of the RepRap 3D printer we just built is that you should be able to print as many of the components as possible. So you can use your 3D printer to build other 3D printers. As a consequence, the printer does not come as a nice little box. It looks a bit jury-rigged. Multicolored coils of wire snake everywhere; circuit boards and integrated chips are exposed; nuts, bolts and stainless steel rods are accessible for easy adjustment; and the plastic–printed–components are still rough from the printer. It is all function, no aesthetics. All of which make it a wonderful teaching tool.

The three students who built it got a crash course in robotic assembly. They learnt how to wire a power source, strip and solder wires, and construct the motor-controlled bed and extruder. They also learned how to use constructive solid geometry (using OpenSCAD) to create 3d shapes–I required them to design and print their own models before I would let them download object files from the internet.

On the down side, though they did have to plug a RAMPS motor shield, stepper-driver chips, and connecting wires into the Arduino microcontroller, we did not have much time to go into the detail of what it all was about. Also, we only edited an existing configuration file when we tried to calibrate the machine, so they did not learn how the programming works. Having to use the Arduino did inspire me to get one, and I was quite impressed with their starter kit, so I’m working on a “Microcontrollers for Beginners” type class or elective that I can offer over the next school year.

Arduino for Beginners

Arduino UNO connected to a breadboard from the starter kit.

I’ve been avoiding working with the Arduino microcontrollers because I’d prefer to be able to program in Python with the Raspberry Pi (for example). However, since the 3d printer we just built this summer uses an Arduino for a brain, I broke down and picked up the Arduino Starter Kit (via Adafruit).

The Arduino Projects Book is an excellent resource for the beginner.

What I liked most about the Starter Kit most is the Arduino Projects Book that comes with it. It’s a wonderful introduction to circuits, electronics, circuit diagrams, and microcontrollers at the beginners level. If I offer an Arduino elective, I’ll use it as a textbook. Indeed, I’ll probably use bits of it as a reference when I teach circuits in middle school and Advanced Physics.

As for the programming, the basics, at least, are pretty straightforward. I got a blinking LED controlled by a switch input up an running pretty quickly. The code requires two loops, one to set up the inputs and the output, and a loop for the program to follow. The code below has a blinking light that’s controlled via pin 4, but changes to a solid light when the switch is pressed (the input for the switch is pin 2). The wiring for the circuit is shown in the picture at the top of the page.

blink_circuit

int switchOn = 0;

void setup(){
  pinMode(2, INPUT);
  pinMode(4, OUTPUT);
}

void loop(){
  switchOn = digitalRead(2);
  
  if (switchOn == HIGH) {
    digitalWrite(4, HIGH);
  } else {
    digitalWrite(4, LOW);
    delay(500);
    digitalWrite(4, HIGH);
    delay(200); 
  }
  
}