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


Assignment 6
Title: Quantitative Generation and Measurement of Light with Arduinos/Teensy's, LEDs, and Photodiodes
and Signal Conditioning Using Operational Amplifiers

The goals of this assignment are:

a. Explore the use of LEDs and photodiodes as light detectors for applications as radiation detectors.
b. Introduce a very common, and extremely useful integrated circuit for electrical signal conditioning, the operational amplifier.
c. Reinforce how you can get quantitative measurements from the Arduino microcontroller.
d. Reinforce the difference between ideal voltmeters and real voltmeters, that meter input resistance matters

Description of the circuit for the photoresistor test, used in the previous assignment. Click on the image for a larger version.

A. We will replace the photoresistor with an LED, now with the LED being used as a wavelength selective detector in addition to as a light source.
Build a simple circuit with a resistor and LED as a photodetector so that you can measure the photocurrent from the LED such that 0.1 microamps produces a 1 volt signal.
You can use the sketch for the photoresistor response time measurement, and CoolTerm for this lab too.
What resistance value are you going to need to 'program' the voltage output this way?
Record the waveform for the LED as a detector with the output of the LED being measured as the voltage across the resistor.

B. Construct transimpedance amplifier circuit with an op amp to convert the photocurrent from the LED as a light detector to a voltage so that a photocurrent of 0.1 microamps produces a 1 volt signal.
Use the sketch from part A to analyze the response time of the photodiode with the transimpedance amplifier used to condition the signal from it.
Write your data to a file using CoolTerm.
Graph your time series. Compare the time response and noise of these circuits.

Board for the Op Amp lab. Click on image for larger version.

Photograph of the Arduino set up measurements with an opamp as a signal conditioner. Click on image for larger version.

C (As time permits: extra credit). Set up the non inverting amplifier circuit with a feedback resistor of 2k Ohm and 2.2uF capacitor in parallel, with a resistor of R2=10 MegOhm.
Measure a pulse from the LED using the same Arduino program we used for testing the photoresistor.
Show the effectiveness of shielding the circuit with aluminum foil. Photograph of the set up, and example data.

D. Analysis.
a. Compare pulse waveforms measured as in parts A, B, and C (if C is pursued).
b. Discuss the operational amplifier 'golden rules' and derive the equation used to obtain the output voltage relationship with the light detector photocurrent.

Use of light emitting diodes as wavelength specific radiation detectors,
as they are very useful for use in simple sun photometers, among other applications.

Discussion of operational amplifiers.

Input impedance of a transimpedance amplifier and local backup.

Photodiode technical information sheet.
OSRAM BPW34 photodiode data sheet.



Assignment 5
: Presention on an Atmospheric Instrument

a. Become more familiar with atmospheric instruments important for your research and/or interests.
b. Share that knowledge with others in class.
c. Become familiar with presenting instrument descriptions.

Your presentation should consider the following:
a. Why you are interested in this instrument.
A. Instrument description, what does it measure?
B. What is the operating principle of the instrument?
C. What sensor(s) are used for the measurements?
D. What is the measurement range and uncertainty?
E. What factors affect measurement accuracy?
F. What are the size, weight, and power use of the instrument?
G. How does the instrument store data?
H. Provide measurement examples.
I. How is the instrument calibrated?
J. Provide other pertinent information.
K. How do the results from this instrument compare with others?
L. References

Action Plan:
Choose an instrument and ok it with the instructor (DOE ARM Site suite of instruments provide a good list of current instruments).

Instrument Manufacturers and other links:
Apogee instruments.
Droplet Measurement Technologies.
Spec Inc.
Comparison of instrument for precipitation type discrimination. (from here).

Students and topics for this assignment
Student Topic



Assignment 4
Arduino, Teensy, and Atmospheric Measurements:
This assignment will be submitted in 3 parts, see webCampus,
parts 1&2; parts 3&4; parts 5&6

Here is what is expected in report writing.

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.

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 to write your own code, or
here's an example sketch that does the calculation in Lux, read through it so you understand it.

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.
Obtain an approximate value for the time constant of the photoresistor as a sensor of light from a graph of the data.

The light intensity is calculated 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.

As time permits, 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?

Be sure to photograph your setup and use it in your report.

3. Do Circuit 7, pg 44 in the book to be become familiar with the TMP36 temperature sensor.

Answer these questions in your write up.
What is the principle of operation of the TMP36 temperature sensor? How was its signal obtained?

Obtain and discuss 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.
First use the sketch for circuit 7 to view the measurement. Then proceed with the sketch mentioned below the figure

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.
Note especially the way that time averaging is implemented in the sketch with the function at the bottom of it, and the difference in this sketch compared with the one for circuit 7.
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.
Obtain and discuss 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.

Presentation on the TMP36 temperature sensor principle of operation

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).

Answer these questions in your write up.
What is the principle of operation of the thermistor temperature sensor? How was its signal obtained?
Obtain the time constant for the sensor as you are warming it up with your fingers, and the response time as you are cooling it off by letting it sit in air.

You might also be able to put the board and sensor into the freezer or toaster oven (on low heat setting) and do the measurements for the response time that way.

Measure the diameter of the TMP sensor and the diameter of the thermistor sensor, and estimate the ratio of the mass of each sensor assuming they have the same density.
Also determine the ratio of the surface area of each sensor.
Calculate the ratio of the response time of the TMP36 sensor to that of the thermistor sensor, one ratio each for heating and cooling.
Does the ratio of response times compare mosty closely with the surface area ratio, or the mass ratio?

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.
Obtain 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.

Thermistor presentation

5. Set up a circuit and sketch to acquire data from the pressure sensor.

Answer these questions in your write up:
How does the pressure sensor work?
Can you see measure the pressure difference between the lowest level you can get it, and the highest level?
Is that pressure difference correct?

Is the pressure sensor properly temperature compensated?

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 by moving your hand over the temperature sensor quickly, using Labview or cool term by doing a screen capture or other means.
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.

Extra Credit Ideas (project ideas):
1. Develop a weather hardened version of the infrared sensor by 3D printing a housing for it and a Teensy 3.6 microcontroller.
Here are examples.
2. Develop the differential pressure sensor into a windspeed measurement tool. Discussion 1. Discussion 2.
3. Develop a gust probe for turbulence measurements. Paper 1. Paper 2.

Additional Resources:
Description of the Arduino and some sensors we'll use.
Discussion of microcontrollers in general.

TMP36 temperature sensor data sheet.
Presentation on the TMP36 measurement principle.

Thermistor presentation

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

Click on image for larger view.

Useful Presentations Collected from Others that describe the Arduino and uses.
Microcontroller fundamentals.
What is Arduino, view 1?
What is Arduino, view 2?
Spark fun intro to Arduino.
Spark fun data collection with high altitude balloons.
Maker and Arduino philosophy.



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.



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.
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.
Another discussion of abstract writing.

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

Methods: 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.

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.

NOTE: Figure and equations should be placed where they are first needed and mentioned in the text.

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.



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