MTI FALL 2010By: Rohan Sharma

Mini Project Documentation: Bacterial Growth Monitor

Concept Development/Background:The idea for the use of my device came about from a

recent experiment we did in Bio LabBasic idea of experiment was to insert a gene

(luciferase) into a strain of bacteria (E. coli) in order to allow them to glow in the dark

Students were asked to take plates of the mutated bacteria home and record the time they initially displayed luminescent properties

The problem: this process can take anywhere from 48-96 hrs(!)

Since it wasn’t realistic to expect students to simply sit around and stare at their cultures and wait for them to glow during this period, all of the students’ recorded times became rough estimates, resulting in less accurate experiment documentation…

The Solution: A device which could sense precisely when the bacteria began to glow + trigger a mechanism that would alert the student

Instructions for use:Simply put the test tube containing bacteria into box and wait!

Basic Breakdown of how it works:

START: Photocell detects brightness of Bacterial Culture (or LED controlled by Potentiometer)

DC Motor was programmed to switch on after photocell detected certain threshold

Mechanism was attached to DC Motor to convert rotational motion to linear motion

Wooden stick travelling in linear motion rings alarm/bell/wakes up student through poking

FINISH: Student knows exact time culture is ready

Critical Components:-Arduino + Breadboard + USB Cable

-Box or vessel to hold test tube of bacteria (must be closed to prevent external light from entering and invalidating results)

-Photocell

-DC Motor + H-bridge

-Mechanism for converting rotational motion into linear motion

-(For demonstration purposes) an LED + Potentiometer to simulate when the bacterial culture was dark and when it reached a certain brightness

-Resistors

-Wires

Other Materials That Were Used:

-Electrical Tape-Wood Glue-Plastic Lid-Paint-X-acto Knife-Paperclips-Velcro Stickers-Wooden Sticks

Building Instructions:1.Once you have all the critical components, a hole must be cut

out of the back of the box in order to connect the USB port. Other smaller holes must be cut into the front of the box to allow motor and potentiometer wires to be attached. The last holes I made were used to put 2 small wooden sticks through the sides of the box in order to prop up the breadboard (see side view)

2.Next, I cut out two ‘arms’ out of cardboard, and glued them to both sides. Then, after poking a wooden stick at the end of both arms to support mechanism later, I glued a paperclip to the end of the stick whose side the mechanism would later be attached to. This was done in order to prevent stick from sliding off when motor is turned on.

3. The next step was to actually make the mechanism for converting the rotational motion of the DC motor into a linear motion which could ring a bell, etc. In order to do this, I used a plastic lid and simply cut a hole at its center. A wooden stick was then attached to the edge of the plastic container by inserting a paper clip through both. This was crucial for allowing free rotation of the wooden stick. The end of the paper clip was then bent in order to prevent the stick from falling off.

Building Instructions (cont’d):4. After this, I attached the plastic lid onto

motor simply by sticking end of motor through the hole I had cut. Next, I used Velcro stickers to attach the DC motor to the box. The same method was used to attach the potentiometer to the front of the box as well.

5. I then cut the box open along 3 edges and unfolded them slightly. The Arduino attached to breadboard was then placed inside (refer to following slide for wiring schematic), using the two wooden sticks as support. Next, I plugged in USB port through back and taped edges of box back together.

6. Lastly, I turned on potentiometer to watch the motor run!

Wiring Schematic:Here is what the Arduino + Breadboard looks like before being placed inside box:

Programming Code:int motorPin1 = 8; // left motor pin wired to Digital Pin 8int motorPin2 = 7; // Right motor pin wired to Digital Pin 7int photosensor = A1; //Photocell hooked up to Analog Pin 1int ledpin = 13; // LED connected to Digital Pin 13int sensorValue = 0; // initial sensor valueint potPin = A3; //Potentiometer wired to Analog Pin 3int potentiometerValue = 0; //Initial Potentiometer Value set to 0void setup(){ Serial.begin(9600); pinMode(photosensor, INPUT); //declares Photocell as Input pinMode(motorPin1, OUTPUT); //declares left motor pin as Output pinMode(motorPin2, OUTPUT); //declares right motor pin as Output pinMode(13, OUTPUT); //declares LED as Output}

void loop() { int brightness = analogRead(photosensor); // defines photocell output as a function of LED brightness int speed = map(brightness, 0, 400, 125, 255); //defines motor as a function of photocell output +

maps output values analogWrite(motorPin1, speed); analogWrite(motorPin2, 0); //allows only the left motor pin to rotate , corresponding to photocell output digitalWrite(13, HIGH); // sets LED to ON position as default potValue = analogRead(3); // defines potentiometer value as value coming from Analog Pin 3 analogWrite(13, potValue/4); //Made LED dependant on potentiometer value (value was divided by 4 to

allow to fit into byte) speed = constrain(photosensor, 0, 100); // constrains motor to run on photocell output of ’20’ or higher Serial.println(analogRead(photosensor)); // prints current output of photocell}

Biggest Problems Encountered:-Initially light from Arduino board kept setting off

motor when placed inside box, so electrical tape was used to cover up these lights

-Putting all the components inside the box was too difficult, so edges had to be cut and folded back to allow more room to work, then later taped back

-Calibrating the photocell to produce an OUTPUT value that was low enough to detect an LED when it was switched on by the potentiometer, but high enough not to have the motor be set off too easily, required some playing around with the ‘map’ and ‘constrain’ functions; eventually a value of ‘20’ was found to work

Possible Improvements/Future Ideas to Play Around With:Have speed of motor correspond to

brightness/number of luminescent bacterial cells

Wire LED’s to outside of box and program to brighten or dim in relation to culture growth

Have sensor output send wireless signal as text message or email when cultures are ready