{"id":7916,"date":"2013-02-28T01:00:27","date_gmt":"2013-02-28T11:00:27","guid":{"rendered":"http:\/\/darkerview.com\/wordpress\/?p=7916"},"modified":"2013-02-28T08:10:39","modified_gmt":"2013-02-28T18:10:39","slug":"laser-spirograph","status":"publish","type":"post","link":"https:\/\/darkerview.com\/wordpress\/?p=7916","title":{"rendered":"Laser Spirograph"},"content":{"rendered":"

With an upcoming open house<\/a>, everyone around the observatory is frantically trying to get everything in place. There will be all manner of science exhibits throughout the observatory headquarters complex. Exhibits about our research, controlling the telescopes, an IR camera display (Get your portrait in IR!), liquid nitrogen ice-cream, just a lot of fun.<\/p>\n

\"Laser<\/a>
A two mirror laser spirograph build<\/figcaption><\/figure>I am coordinating an exhibit we named Optics Lab… As you would expect, most of the exhibits in our area teach basic optics, light, lenses, etc. Understanding light and optics is a basic skill in a large observatory. We will have a few lenses on rails, a laser ray-trace table with acrylic lenses, an exhibit on polarization, and even a simple laser interferometer.<\/p>\n

When attempting to teach something, a little eye-candy is helpful to catch the attention of the audience, particularly kids. Our group includes a laser engineer and a laser tech, so the use of lasers was obvious. There is little that catches the eyes of a kid faster than a bright laser beam. One of the first ideas they tossed on the table was a laser spirograph<\/a>. After a few moments thought the answer was clear… I can build that!<\/p>\n

\"SpiroLaser<\/a>
Schematic for the SpiroLaser control PCB<\/figcaption><\/figure>Time to dig about in the scrap box! Actually more than a few boxes in my case, I am a bit of an electronics pack rat. A green laser module… Check! Small DC motors… Check! A few voltage regulators… Check! A couple potentiometers… Check! First surface mirrors… Check! In an hour of rummaging about I quickly located everything that was needed.<\/p>\n

The circuit is very simple… There are three LM317 voltage regulators side by side. One regulator is set to three volts for the laser module, the remaining two are configured as variable regulators for the motors. <\/p>\n

Experimentation was needed to find the operational range of the motors. The old tape recorder motors from my scrap box ran very nicely on anywhere from 4 to 16V, giving a nice range of speeds in the process. The motors are also double housed, running quietly. Well… at least they were quiet after the addition of a little light machine oil in the bronze bushings, these motors had been sitting in the scrap pile for at least two decades. When I first applied power I thought I might have to toss them they ran so rough!<\/p>\n

\"Laser<\/a>
A laser spirograph pattern projected on the ceiling<\/figcaption><\/figure>The power supply is a leftover 19V laptop power supply. This allows for the 15V motor voltages and plenty of power. The variable regulators are configured for 6 to 15V, see the schematic for the resistor vales. The potentiometers are ten turn style, allowing a fine adjustment.<\/p>\n

The variable resistors for motor speed control are located in a remote box. This allows the projector itself to be placed just out of reach, but allows access to the controls for curious young minds to play with.<\/p>\n

\"SpiroLaser<\/a>
Mechanical layout for the Spirograph Laser<\/figcaption><\/figure>One item caught me by surprise, the laser module takes more power than I expected to run. As a result the LM317 used in the laser regulator was quite hot without a heatsink. The current plus the 19V supply voltage added up to a fair amount of power dissipation. I modified the board to add a heat sink for this part.<\/p>\n

The frame was the result of an evening in the machine shop. I wanted a first class build here, something that can serve as an exhibit for more than this one event. Rummaging about the shop yielded some 1″ thick acrylic and scraps of aluminum that make for a very nice base. The laser module case is not electrically isolated, thus a plastic mount is a good idea, may as well make the motor mounts out of the same material.<\/p>\n

The unit can be positioned to project the beam vertically or horizontally. I expect vertical to be the usual orientation, the pattern is projected on the ceiling for all to see. This keeps the beam away from any eyes, even though the beam is under 5mW and reasonably eye-safe.<\/p>\n