Dylan Hatt University of Chicago – Department of Astronomy & Astrophysics The outline of this document is as follows:

1. More about the CFF 2. Purchasing your Arduino & Arduino alternative 3. Building your Arduino 4. Dark room activity 5. Analyzing the data 6. Notes

1. More about the CFF

There are several factors that influence reaching one’s CFF, or the point at which a changing stimulus is perceived as steady. These include (via Wikipedia circa 2014):

i. the frequency of the modulation; ii. the amplitude or depth of the modulation, i.e., what is the maximum

percent decrease in the illumination intensity from its peak value. This is related to the diffuseness of the light when it is projected onto something like a wall;

iii. the average (or maximum-these can be inter-converted if modulation depth is known) illumination intensity;

iv. the wavelength (or wavelength range) of the illumination (this parameter and the illumination intensity can be combined into a single parameter for humans or other animals for which the sensitivities of rods and cones are known as a function of wavelength using the luminous flux function);

v. the position on the retina at which the stimulation occurs (due to the different distribution of photoreceptor types at different positions);

vi. the degree of light or dark adaptation, i.e., the duration and intensity of previous exposure to background light, which affects both the intensity sensitivity and the time resolution of vision.

The first factor is subject of study in this laboratory.

2. Purchasing your Arduino & Arduino alternative

The total cost associated with the Arduino is $50-$100, assuming the instructor already has access to resources like a soldering tool. The essential components to the laboratory are:

1. Arduino 2. USB cable (connecting Arduino to computer) 3. Buttons 4. Potentiometer knobs 5. Resistor and blue LED 6. LCD screen

Arduino starter kits are available on Amazon for $50-100, which also includes the LCD screen. The likely missing items are a blue LED and two potentiometer knobs. A blue LED can be purchased through Amazon as well, but for a single LED, we recommend searching a local hobby store first. We have found that an inexpensive blue LED (< $1) works well enough for this laboratory. The potentiometer knobs can also be purchased online through Amazon. Scroll through the images in this document to verify that you’re purchasing a comparable product. For this laboratory we have also developed an Adobe Flash program that is able to run on computer and most mobile devices. There is a limit to the screen refresh rate of computer and mobile devices. We have set the maximum frequency of the program to 30 Hz.

To operate the activity, choose whether the blinking light should start from blinking or steady. When your CFF have been reached, click the light and the frequency will appear on the screen. Click the bottom of the screen at any time to return to the main screen.

3. Building your Arduino

Before we begin putting the circuit together, please follow the below instructions to run the code that controls the Arduino:

i. Download Arduino software from http://arduino.cc/en/Main/Software ii. Once installed, open arduino.exe iii. The Arduino code can be found at http://kicp… Copy and paste the code

into the Arduino program window and save. iv. Connect the Arduino circuit to computer using a USB connector and then

click upload button in Arduino program. If there are no errors (e.g. wrong COM port), then the code has been uploaded to the Arduino correctly.

We now begin to gradually piece together a functional circuit. Initially, we will simply make an LED shine.

i. Connect the plug labeled “5V” on Arduino to the end of a column labeled “+” on the breadboard by placing the metal ends of the wire into the small gaps. This will provide voltage all that way down that column.

ii. Connect plug labeled “GND” to the neighboring column (same row) to the “+”, this time labeled “-”. These allow current to flow into the breadboard and exit via the “electronic ground”.

iii. Choose a resistor to reduce the overall power that will eventually be used by the LED (this will help conserve the battery’s energy). We used a 330 Ohm resistor. Connect one end of the resistor on the “+” row and the other onto the breadboard itself.

iv. At this point one could simply place the long end of an LED into the same row as the resistor and the other end into the ground column “-“, but we will add an extra step to prepare our circuit for later use. Connect a wire to the same row as the resistor and put the other end into plug ~11 on the Arduino. A wire can then come out of plug 12 on the Arduino and into another row on the breadboard.

v. Connect the long end of your LED (known as the positive end) to the breadboard in the same row as the wire coming out of plug 12. The other end of the LED should be placed into another row. We wished to reduce the power generated by the LED even more, so the negative end of the LED (the one currently in a row by itself), will be now be in the same row as a resistor (we use about the same 330 Ohm as before). The other end of the resistor will then go to ground, or the “-“ column.

vi. Connect your 5V battery to the Arduino and your LED will be

illuminated! vii. Note in the image above  that we  decided to solder wires onto the LED.

This allows the LED to be more flexible and stand well above the circuit.

We are surprisingly already half the way done with this circuit! We now wish to make the LED blink.

i. We need to tell the Arduino to stop sending current into the breadboard, then after waiting a brief time, continue sending current, and so on. The code already has the framework to vary between 0 and 100 Hertz (Hz or times per second), but it can be adjusted to your needs. Our second potentiometer will send a varying amount of current to the Arduino, which will interpret convert it to an actual blink frequency. To begin, disconnect the battery to the Arduino.

ii. Solder three wires onto your potentiometer. Connect the rightmost wire into the “+” column so that it will draw from the power supply. The middle wire will connect into the port A0 on the Arduino (this port can be changed into the code). Connect the leftmost wire to ground in the column “-” as before.

iii. Reconnect the battery and adjust the second potentiometer to change the blink frequency! Note that you might need to change what you consider the rightmost and leftmost wire depending on the orientation of your potentiometer!

We will now add potentiometer to control LED brightness, which will allow us to dim the LED for dark room vision.

i. Disconnect the battery from the Arduino before we begin. ii. Solder three wires onto your second potentiometer. In the same row as the

wire from plug 12, connect the rightmost wire from your potentiometer. The middle wire will feed into a new position of on the breadboard, and the leftmost wire will go into the column “-” so that it goes to ground.

iii. Reinsert the long (positive) end of your LED into the row with the potentiometer’s middle wire. The other end of the LED will be in the same row as the resistor that is also connected to ground.

iv. Note in the image above that we have added an extra wire at the very top that connects the “-“ column to that on the right. To avoid cluttering we now plug the leftmost wire of the second potentiometer into the other “-“ .

v. Reconnect your battery to the Arduino and move the dial on the potentiometer to adjust the brightness of the LED!

At this point your circuit should be adjustable in its blink frequency and brightness. We would now like to attach the LCD screen and button in order to measure the frequencies when we reach our CFFs.

i. Disconnect the battery and connect one end of the button to the “+” column and the other to ground. In the picture below, we chose to use the second “-“ column. Note that you might have to switch the button wires just as with the potentiometers.

ii. Connect the red end of the LCD screen into the “+” column, the yellow

into the port TX->1, and the black to ground. Note that you are able to use additional wires to allow the current to flow to the right part of the circuit if the original cable does not reach.

iii. The code already it setup to be compatible with the LCD screen, so reconnect the battery and enjoy!

4. Dark Room Activity

Sufficient adjustment to the dark room can take of order 5 minutes or more. We recommend the instructor make use of this time by doing the following activities.

i. Ordering colors: Our perception of what is dark or bright is created by the sensitivity to our photoreceptors cells to particular wavelengths (see figure below). Rod cells see shorter wavelength best, hence why it is difficult to see certain colors such as red in the dark. To demonstrate this effect, have students order a series of colored construction paper from lightest to darkest in normal or semi-bright lighting. Repeat the ordering in the dark room once students begin to adjust. Later when the lights are turned on, the two ordering may be compared.

(Dowling 2012)

5. Analyzing the data

6. Arduino Notes i. LED: The rate of turning the LED on and off is on the order of

microseconds while the response rate of the eye is 10-100 ms, depending on the primary photoreceptor cell in use.

ii. Our LCD screen was able to output 10 values at a time. For large classes, these data values will need to be recorded before continuing since the LCD will erase its previously stored values.

iii. At any point, the Arduino can be reset by pressing the small black button on the top of the circuit.