For the laser instrument, the team plans on utilizing laser diodes as an innovative implementation of musical instrument keys. Instead of having to press a button to play a musical note as one would do for most standard instruments, the laser instrument would rely on breaking the light beam of a laser diode. When a laser diode is prevented from emitting light onto a photo sensor, the laser instrument would produce a musical note. This process would be synonymous with pressing a key on a standard musical instrument.
3.2.1 Research
The most common laser diodes that would be feasible options for this project are red laser diodes and green laser diodes. These wavelengths of laser diodes were the most available at the time of research and development for the laser instrument project. Each laser diode has its own advantages and disadvantages that must be considered to determine which would best fit the scope of the laser instrument project.
3.2.1.1 Red Laser Diodes
Red laser diodes emit light in the red spectral region with a wavelength ranging from about 625 nm to 700 nm. Hobby level red laser diodes typically come in wavelengths of 635 nm, 650 nm, and 670 nm. Shorter wavelengths overall provide easier visibility to the human eye but can potentially pose more difficulties when it comes to efficient generation of the laser [8].
Compared to their green counterpart, red laser diodes are usually cheaper and more readily available. This will contribute to the affordability aspect of the project outlined in the Project Description. Given that the project also aims to be portable, the red laser diode’s lower power consumption would allow for a frame design and power supply component that are not as space consuming or high temperature emitting. The diodes themselves would not demand excessive amounts of space in the frame as well making them an additionally appealing choice. Even though red lasers have a lower visibility to the human eye compared to green lasers, this project does not require the extra visibility that would warrant a green laser to make a significant difference in comparison [9].
Figure 11 Adafruit (left) and HiLetgo (right) Red Laser Didoes Permissions in Figure 33 and Figure 34
The laser instrument project does not require industrial-grade laser diodes, so the red laser diodes researched were hobby level. The two considered were the Adafruit 5 mW 650 nm Red Laser Diode pictured left in Figure 11 and the HiLetgo 5 V 650 nm 5 mW Red Diode Laser pictured right in Figure 11. The tubing that
encases the red laser is the most significant distinguishing factor between the two different versions aside from the cost per unit of each. Both operate with similar voltage and current specifications and emit a laser with a similar dot shape.
However, despite the many commonalities in their operation and performance, the Adafruit laser diode has larger tube dimensions [10]. The size of the laser diode tube chosen would directly affect the size of the instrument’s frame, so this aspect of the laser diodes’ shapes must be considered during the part selection for the laser instrument. Keeping this in mind, a smaller diode would be preferable for this project.
3.2.1.2 Green Laser Diodes
Green lasers emit light in the green spectral region with a wavelength ranging from about 510 nm to 570 nm which would be suitable for several photo sensors to read [11]. Despite red lasers being more common in use than green lasers, green lasers can shine up to four times brighter which would make it easier for users to see exactly which diode, or diodes, they are blocking in ambient light. For the purposes of this project, the laser diodes implemented do not require a far reach in order to have a successful laser instrument. Green laser diodes do not have as many suppliers or demand in comparison to their red counterparts. This in conjunction with the fact that green laser diodes have a higher power consumption and produce more heat make it hard to support mass producing. The higher cost of a green laser diode would also conflict with the affordability aspect of this project [12].
Figure 12 Digi-Key (left) and Lights88 (right) Permissions in Figure 36 (Lights pending permissions)
While researching various green laser didoes for comparisons, there were limited options for hobby lever laser diodes. The few laser diodes found that were in the scope of what the laser instrument project requires had higher price points per unity and larger tube dimensions. The Digi-Key VLM-520-28 LPT, pictured left in Figure 12, has a tube length of 33 mm and diameter of 9 mm. The price point per unit at the time of research was $34.95 [13]. The most comparable pricings for green laser diodes were found on Amazon that still had more expensive price
points when compared to red laser diodes. At the time of research, the Lights88 532nm Green Laser Module Diode, pictured right in Figure 12, had a unit price of
$16.89 [14]. Although the price point was more reasonable compared to the Digi-Key green laser diode, the Lights88 laser diodes had a longer tube length compared to red laser diodes at about 31 nm.
3.2.2 Technology Comparison
Red and green laser diodes each have advantages and disadvantages that would contribute to the goals and requirements of the laser instrument project. Since the laser instrument only requires a laser diode to emit a light beam no more than 2 feet, the distance at which a green laser diode’s performance would supersede a red laser diode’s performance would be beyond what the project would utilize.
Table 10 Laser Diodes Comparison
HiLetgo Adafruit Digi-Key Lights88
Tube Length 18 mm 31 mm 33 mm 31 mm impact the project’s goals and objectives as well as the design. The green laser diodes mostly offer a more vibrant light beam that has a better chance of being viewed by the human eye in ambient light in comparison to red laser diodes. This would be an attractive feature for the laser instrument as it would potentially add another layer of visibility to the user while playing notes. However, this potentially nice extra feature that could be incorporated in the design of the laser instrument does not offset the exponentially higher price difference between the red light emitting laser didoes and the green light emitting laser diodes.
With the green laser diodes eliminated as options due to their conflict with maintaining affordability without greatly sacrificing the quality of the project, the HiLetgo and Adafruit red laser diodes are the remaining choices. Although the Adafruit laser diode has a slightly higher unit price compared to the HiLetgo laser diode, the length of the diode tube was more of a concern for the team. A longer tube length would mean the instrument frame would have to overcompensate its dimensions to fix the component and any supporting electrical wiring. This could potentially limit the team’s flexibility later in the design process or negatively impact the portability aspect of the laser instrument.
3.2.3 Part Selection
After reviewing the various options for green laser diode and red laser diodes, the team quickly decided a red laser diode was the best fit for the project. Of the red laser diodes researched, the HiLetgo 5 V 650 nm 5 mW Red Diode Lasers were chosen for the laser instrument project. The HiLetgo laser diodes satisfied the team’s goals and requirements for the projects without stepping out of bounds of any established constraints. These laser diodes were a reasonably priced component with compact sizing that allowed more flexibility during the prototyping and testing phases of the project.