Spectrograph

The purpose of this design project is to update the Engineering Physics 3G03 Project designed by students Yu Lou, Wei Cui and Paul McMullen. This project can be used as a future representation of some of the work students in the photonics stream of Engineering Physics are involved in during their undergrad career.

The objective of the spectrometer design project was to construct a spectrograph that can resolve the wavelengths of several LEDs in the visible region of the electromagnetic spectrum. The primary objective is for the project is to resolve the LEDs individually, while the secondary goal was to be able to resolve two or more LEDs simultaneously. The spectrometer was to cost less than $200.00 and have no moving parts. The spectrograph was to be able to plot intensity [Volts] versus wavelength [Nanometers], to aid in the description of the input light.

The original project can be found here.

There were several things discussed to make the spectrograph more demo ready. During in class testing and during a presentation, the LEDs being resolved were plugged into a bread board which was powered by AA batteries. This was impractical since it contained additional loose components as well as an additional power source which could run out. The first update was to have a computer power the LEDs, and have the LEDs placed inside the spectrometer. Additionally, the circuit was still on a bread board so it needed to be soldered to a PCB. These are some of the major changes that were the most important. The following are the details of the updates.

Before beginning to work on the definite changes needed, the housing box needed to be recreated. There were several parts that did not quite fit properly and could be made better for a more aesthetic appearance. Several pieces were replaced with newly cut pieces of hardwood.

LEDs were added to the front of the system each with a switch to verify which colour of LED is on. These holes were drilled into the hardboard using a drill. The box was reconstructed, leaving some pieces with a black finish and others without. The switches and LEDs were placed in their respective positions before repainting. Everything that was not to be painted was covered with duct tape, and the housing was spray painted with two coats of paint.

After the paint had dried the duct tape was removed. At this point, all wires were removed from the breadboard and were soldered into a two separate PCBs: one for the detectors and another for the LEDs. The schematic diagrams for the detectors can be found in section 2.5.

In the original design, the microcontroller only had 6 analog inputs. This was not sufficient enough for resolving the LED. To solve this problem, we used a break in the program and several switches to store 10 data points instead. Since this method was confusing for the user, a larger microcontroller was acquired with 16 inputs. This would improve the resolution of the spectrograph, and hoped it would likely make the programming easier.

First, the GUI was remade to remove the unnecessary functions from the previous spectrograph. These include all the various methods of interpolation. The cubic spline was left and used for representing the data. Turning LEDs ON/OFF using the interface was considered, but it was simpler to just use the mechanical switches. Problems arose when trying to connect the ARDUINO MEGA to the computer. The error message implying the microcontroller was not connected or available kept appearing. This problem seemed relevant only to the MEGA, as switching back to the UNO resulted in no problems. The adiosrv.pde code was inspected and altered to try to get a connection to the MEGA but this was not possible at the time. The old set up was used again, replacing the MEGA with the UNO and its 6 analog ports. Because of this confusing set up, detailed operating instructions can be found in section 2.4.

The optics inside the spectrometer was realigned for the new configuration and parts. The MATLAB program was fixed to work for the UNO and the results were tested. The spectrometer resolves a single LED at a time, using MATLAB, and produces a result, indicating which colour the LED is. The spectrograph only distinguishes between red, green and blue LEDs.