Open Source Monochromator: Difference between revisions

Understanding the market

Monochromators are used in optics to isolate certain wavelengths from a light source made up of many wavelengths. ^[1] Monochromators on the market are anywhere from $2000 to $10,000. Our monochromator is made for less than $100.

Project goals

The goal for this project was to create an easily 3D printed and assembled monochromator that is still relatively accurate.

Design

• Monochromator Parts
• 

  Monochromator Wall

• 

  Monochromator Base Plate

• 

  View of diffraction grating

• 

  View of concave mirrors

• 

  View of enclosure front

• 

  Top view of monochromator

Mechanical Assembly Instructions

1. Purchase mirrors, bolts, nuts, razor blades, stepper motor, and associated electronics
2. Print files from NIH site http://3dprint.nih.gov/discover/3dpx-002158
3. Epoxy mirrors into printed mirror holders and leave until dry
4. Cut 1" by 1" square from edge of DVD-R and epoxy to mirror holder face
5. Epoxy 16mm M3 bolt onto end of stepper motor
6. Push M3 nuts into pockets on back of front wall
7. Bolt razor blades onto wall with sharp edge pointed into center of wall
8. Bolt stepper motor to wall using 4 bolts, with 2 washers under each bolt
9. Bolt wall to base with 2 M3 bolts
10. Push first mirror holder into square slot on base pointed toward front wall and insert bolt from underneath to secure, repeat with second mirror holder
11. Push M3 nut into pin for diffraction grating mount
12. Place pin into arms on diffraction grating mount
13. Place diffraction grating mount into hole on base plate
14. Rotate pin so that the nut side is closest to the stepper motor and rotate the motor by hand to start the bolt into the nut
15. Place assembly into cardboard box, mark out holes for motor and slots
16. Remove assembly, cut out holes, place assembly back in box
17. Tape assembly to bottom and front of box being careful to not cover inlet and outlet slots with tape
18. Proceed to electrical setup section

Electrical Assembly Instructions / Software

1. Wire stepper motor according to this diagram^[2]
2. Program Arduino according to the code below:

#include <Stepper.h>

const int stepsPerRevolution = 200;  // change this to fit the number of steps per revolution
// for your motor

// initialize the stepper library on pins 8 through 11:
//Stepper myStepper(stepsPerRevolution, 4, 5);

int stepCount = 0;         // number of steps the motor has taken

void setup() {
  pinMode(6,OUTPUT); // Enable 
  pinMode(5,OUTPUT); // Step 
  pinMode(4,OUTPUT); // Dir 
  
  // initialize the serial port:
  Serial.begin(9600);
}

void loop() {
  // step one step:
  Serial.println("Please Enter Step Value (-50 to 50): ");
  while (Serial.available() == 0);
  int val = Serial.parseInt(); //read int or parseFloat for ..float...
  if(abs(val) > 50) {
    Serial.println("ERROR: Too High of Input Value.");
    goto failed;
  }
  if(val < 0) {
      digitalWrite(4,HIGH); // Set Dir high
  }
  else {
    digitalWrite(4,LOW); // Set Dir low
  }
  for(int i = 0; i < abs(val); i++) {
    digitalWrite(5,HIGH); // Output high 
    delayMicroseconds(500); // Wait 1/2 a ms 
    digitalWrite(5,LOW); // Output low  
    delayMicroseconds(500); // Wait 1/2 a ms 
  }
  Serial.print("Moved ");
  Serial.print(val);
  Serial.println(" Steps.");
  stepCount++;
  failed:;
  //delay(500);
}

Calibration

1. Due to the many types of mirrors and DVDs available calibration is recommended
2. Acquire a white light source and spectrometer
3. Move the mirror to the maximum and minimum travel and record the prevalent wavelength
4. Take additional points if necessary at known number of stepper motor rotations
5. Use either a best fit linear line or polynomial to calculate wavelength output vs stepper motor rotations

Costs

Discussion

Current Issues

1. Diffraction mount will not actually rotate in current configuration
2. Setup in now too heavy on motor side
3. Motor is also in the way of light openings

Possible Solutions

1. For all problems above move motor underneath and direct mount to diffraction mount

References

Contact details

1. Robert Arden
2. Mike Hartl
3. Michael Patrick
4. Andrea Henry