ATMS 360 Homework and Course Deliverables (return to main page)
[How to write lab report]


 

Assignment 4 Arduino and Atmospheric Measurements:

You will need to acquire data in class, write lab notes about your measurements, and write up each section of the lab
as homework as soon after the section is finished so you remember it in detail. It will be very difficult to write up the lab
after all the experiments are done.

Title: You can decide on the title based on your experience with this lab.

Goals:
a. Become familiar with the Arduino microcontroller as an example of a programmable device for acquiring measurements and controlling systems.
b. Demonstrate ability to modify Arduino sketches for solving problems.
c. Learn about and use sensors with atmospheric relevance.
d. Learn how to bring measurements from the Arduino into computers (interface the Arduino) to acquire data for later analysis and display.

If possible, install the Arduino software on your own laptop (if you have one), and use it in class.
Also download CoolTerm and place it somewhere that you can get to it for ease of use. This program allows us to transfer data from the Arduino to the computer.
The code for the projects in the book and kit is here: expand the file and put the folder in your Arduino examples folder.
Here is a link to the an online version of a manual that is similar to the one we use in class. (local backup).

In your report, describe and/or answer these questions
1. Introduction to describe the Arduino (why is everyone so crazy about this thing?).

Measurements and Analysis
2. Do Circuit 6, pg 40 in the book to learn about the photoresistor and how to measure its output.
Then create a circuit to drive the LED at different frequencies to see if the photoresistor resistance can accurately follow the LED output for low and high frequencies.
Point the LED output directly into the photoresistor input. You can use variable delay and the 'Blink' sketch to drive the LED.


Description of the circuit for the photoresistor test. Click on the image for a larger version.

If the LED is driven by a square wave, the photoresistance should show a crisp square wave too. Use the plot monitor on Arduino to view the photoresistor output,
and save some data with CoolTerm (including time) so that you can graph the photoresistor output from the LED drive as a function of time.
Can you estimate the time constant of the photoresistor as a sensor of light?
Here's an example sketch that may be helpful in measuring response time. You may find ways of speeding it up to get more time resolution on the LED response.

Calculate the light intensity using the equation LUX = 1.25*107*Rp-1.41 where Rpis the photoresistance in Ohms. (local backup of link).
Then work out the response time of the photoresistor for measuring light using the Solver within Excel.

Do one set of curves for room lights on, and another for lights off. Is there any difference in the time constant caused by spanning the photoresistor over such a large range of light intensity?



3. Do Circuit 7, pg 44 in the book to be become familiar with the TMP36 temperature sensor.
What is the principle of operation of the TMP36 temperature sensor? How was its signal obtained?

Description of the analog to digital conversion for the TMP36 sensor. Click on image for a larger version.

Example sketch for response time measurement. Read it and follow instructions. Pinch the temperature sensor to warm it up when the LED comes on.
Record a time series with CoolTerm as you pinch the the sensor to warm it up to a steady temperature, and let it decay to a lower temperature.
Estimate the time constant for the sensor as you are warming it up with your fingers, and the time constant as you are cooling it off by letting it sit in air.

4. Create a voltage divider circuit to measure the resistance of the thermistor sensor using a fixed resistance of 1 MegOhm (1,000,000 ohms).
Calculate the temperature that corresponds to your measured resistance using the equation given here (thanks Alex).
Record a time series using CoolTerm as you pinch the the sensor to warm it up to a steady temperature, and let it decay to a lower temperature.
Estimate the time constant for the sensor as you are warming it up with your fingers, and the time constant as you are cooling it off by letting it sit in air.
Here's an example sketch to use for the thermistor sensor evaluation. Read the sketch for instructions on what to do.
Pinch the thermistor carefully (without affecting the wires) when the LED is on.

Click on image for larger version.

5. Set up a circuit and sketch to acquire data from the pressure sensor. Do appropriate data averaging so that you can easily tell the pressure difference
between having the sensor on the desk, and having the sensor about 1 meter higher or lower. Record data with CoolTerm to demonstrate your results.
Here's an example sketch for the pressure sensor. You'll have to comment out some lines near the end to get only the pressure measurements to CoolTerm.
Do measurements with 1 second time average, holding the sensor down for 10 seconds, then up for 10 seconds.
Then modify the code to obtain 10 second time averages. Test by holding the sensor low for 100 seconds, and high for 100 seconds.
Comment on the effects of additionally time averaging the data.

Click on image for larger version.

Note: It seems the 10 bit analog to digital (a/d) converter of the Arduino would not be able to resolve a pressure difference of about 0.1 mb associated with
1 meter height difference. 1 bit change in the a/d counts corresponds to a voltage change of about 0.005 volts, and a pressure change of and about 1 mb pressure.
Dither helps: the voltage source for the Arduino is noisy enough to cause around 50 mv or so of noise so that the a/d counts fluctuate to a useful average.
The example sketch for pressure averages the measurements of the pressure sensor voltage and the voltage divider voltage about 1800 times for each measurement.
Use of the voltage divider for the power supply voltage measurement is necessary since the a/d range is 5 volts, and direct measurement might be over the measurement range.

If you are ahead, you may add the digital pressure sensor to the sketch and breadboard layout and compare the analog and digital sensors.

6. Implement the infrared sensor. Interface it with Labview using the indicated code.
Demonstrate a time series of temperature from Labview or cool term by doing a screen capture. Include a discussion of how the sensor works.
Those with laptops can take the IR sensor outside to get a time series of infrared brightness temperature of various targets.


Notes on the IR sensor: Click on image for larger version.


Resources:
Description of the Arduino and some sensors we'll use.

TMP36 temperature sensor data sheet.

Very useful voltage divider circuit to use for measuring sensors that depend on resistance.

Click on image for larger view.

 

Assignment 3 Online (see webCampus) measurement of atmospheric temperature.

Purpose: Become familiar with atmospheric temperature measurements.

Assignment 2 Online (see webCampus) overview of Atmospheric Instrumentation.

Purpose: Broad overview of atmospheric instrumentation measurements.
This is an online homework assignment and is described on webCampus.

Assignment 1 Online (see webCampus) atmospheric radar measurements.

 


EXPECTATIONS IN LAB REPORTS

Lab reports will be written the same format we use for scientific papers and for student senior, MS, and PhD theses.
One goal of this class is to work on your ability as a science writer.
Let me emphasize one word here. SCIENCE SCIENCE SCIENCE SCIENCE SCIENCE SCIENCE!!!!
So often we are obsessed with the technical details of the measurements that we don't cover the science adequately.
The following elements are needed for your lab report to be complete.
Here is an example of some hints I found using a google search with the keyword "how to write a scientific paper".
Page length doesn't matter; it's all about the contents.
Make it as short as possible to get the message across in a clear manner.

Title: The title should cover the science objective and maybe mention the instrument(s) used for the measurement.

Abstract: The abstract is a brief discussion of the findings of your work. It should be well written because it is often what is read as someone makes a decision to read your work (or fund your research).
Hint on writing abstracts.

Introduction: Explain the scientific goal in more detail and maybe hint at the measurement methods used.

Measurements: Discuss the measurement methods, including uncertainties.
Discuss the instrument(s) and the pertinent information needed to convey what you measured.

Observations: Display your observations and interpret them for your reader.
Make clear, legible graphs with large fonts, clear symbols, and clearly documented results.

Figures: Provide figures, each figure with a number and caption.
Figures must be in publication format -- high quality figures with 16 point (or greater) bold black font; tick marks inside.
All axes 1 point thick and black.
Each figure must be discussed in the text by number, describing the significance of the figure and its relationship to other figures as needed.

Equations: Equations should be offset, as in a textbook, and each equation should have a number.
Refer to equations by number in the text.

Conclusions: The conclusion should summarize your observations and perhaps make suggestions for future work.

References: References refer to specific articles and/or books, etc, that you reference in your paper.

HERE IS AN EXAMPLE LAB REPORT

HERE IS ANOTHER EXAMPLE LAB REPORT


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