In the past two weeks I worked on finishing up all the systems and mounting them in the box. The last system I had to complete was the laser power control. This system was simply Mosfet transistor with the gate connected to the arduino PWM pin, the drain connected to the cathode of the Laser diode and the source connected to the ground of the power supply.
This was the last electronic system I had to create, and after this was done I could start mounting the systems in my box.
Unfortunately, I did not figure out the optics for the 5W laser yet, so for now I have a red visible laser installed.
In the next week (the last week of school) I will epoxy together all the parts that need it for the final assembly.
I began this week by solving all the problems with the user interface. I fixed a short that was causing it to not work, I wired the lcd backlight directly to 5v and ground, and I attached all the wires of the VGA cable. The UI is now finished.
I focused on the laser this week, I began by creating a holder for the laser diode that will connect to the heat sink.
This will allow us to have optics very close to the diode, which may be required for focusing it, which wasn’t possible with the heatsink we were using before. The “clamp” as i call it, was designed in Fusion360, 3d printed in castable resin in the school’s Form 2 printer, and cast in aluminum.
After this was done I added the TTL laser control circuit.
This circuit utilizes an IRF520 Mosfet controlled by a PWM pin on the Arduino. I added the power control to the arduino program. I mapped the 0-100% duty cycle, controlled witht the UI, to the 0-255 value of the PWM pin.
This week, I built a lot of the physical parts for this project.
First, I printed the frame for the mirrors in Formlabs Clear resin, and I assembled all the mirror components together. After Testing I plan to epoxy the plastic parts together for added strength. I also constructed a steel U-shaped piece that holds the mirror assembly up of the ground.
Second, I deconstructed an old classroom tape recorder to use as a box for this project.
Third, I began to construct the user interface (UI). I drilled holes into 1.5mm steel sheet, and used a dremel to cut out the window for the LCD. I sandblasted the panels and printed a frame to hold the LCD. I also assembled a small circuit board that reduces the number of input/output wires from 14 to 8. The wires are pos, neg, pot 1, 2, 3, and LCD 1, 2, 3. I am using an LCD “backpack” to reduce the amount of wires and space used.
Fourth, and last, I began to assemble the hardware. I acquired an arduino, I began to make an arduino “shield” and a circuit board for the servo wires. A major goal for this project is to have all of the parts to be modular so that I can easily change out parts or in the future, it would be easy for someone to cannibalize the subsystems of this project.
Next week I will be constructing the servo motor mounts and the spools for pulling the string. I hope to have the mirrors operational by the end of the week, April 27.
This week I finished constructing the mirror assemblies for the project.
Now with the mirror assemblies done I have to build the structure that holds them in the right orientation. I initially thought about milling this structure out of aluminium, but the time and effort involved are not worth the outcome, milling it out of aluminium would be overkill. So I decided to print it on my schools form 2 printer.
The frame is four parts that screw together. After this I will build the platform that hold all of the components, and begin assembling the electronics.
This week I finished designing, and began constructing the mirror assemblies for the laser. Below is a picture of one of the mirror assemblies. The assembly is made of two basic parts: the arm which acts like a large pulley to rotate the mirror, the hub, which holds the mirror, the arm, and the bearings/axle.
The arm was milled out of carbon fiber to make it strong, light-weight, and cool looking.
The hubs will be 3-D printed using the school’s Formlabs Form 2 SLA 3-D printer. My next challenege will be to create a frame that will securely hold both axles in the proper orientations.
This week I tested the resolution of the servo motors. I used a basic setup of a servo motor with a mirror glued to the horn and I controlled the servo using /Servo.writemicroseconds()/. First I started by decreasing the size of the pivot of the motor. Through this Test I found that the servo motor’s minimum movement is 20ms, I also found that the servo is very inconsistent at these small movements. Next I used a servo driver module, our thinking was that this module had a better internal clock than the arduino and would give more accurate movements as well as smaller steps. This was not the case the results were the same as using a servo without the driver. Finally I built a rig to test my idea of gearing down the servo motor for more precision. Here is the rig:
Basically, it is a 10:1 pulley system with the mirror mounted on the pivot point. In theory,this should increase the precision of the servo by 10x. Below is a video of the rig cycling through some angles.
With this setup I achieved my goal of 5mm precision at 0.6m.
This week I researched power sources for my laser system. Because a laser is a diode, it has virtually no resistance, so it will keep drawing current until it burns itself out. Because of this, the laser requires a constant-current power source. The first result of my research was a LM317 constant-current power supply circuit (shown below), this circuit is very popular amon laser pointer enthusiasts.
This is a good circuit, however it will not work for my application. The LM317 has a max operating amperage of 1.5 in a 5 volt system. This would work for a 5W laser, however my system will be using 25W, so I continued my research. My teacher recommended a 2-channel power supply from Mouser electronics supply. This power supply can deliver 40W on one channel (which is more than enough for the 25W laser) and the second channel can be used to power the arduino and servos.
Next week I will design a prototype to test having a gear ratio with the servos, and test the mirror’s efficiency with the laser.