alphanumeric laser projector with arduino

The idea of Intro is to make a small, cheap, highly portable (
Battery operation)
Alpha digital high power laser projector.
This will be a device that you can use to project messages on distant targets.
It turns out that in the kickstarter project, including obtaining laser product certification, laser efforts and costs are not worth it. . .
But DIY is fun.
Most of the hardware is implemented using my home\'s basic test and measurement device, except for the oscilloscope I had to borrow.
In most cases, you can achieve this with just a few manual tools, low speed oscilloscope, power supply, and DMMs. .
And soldering iron.
The projector displays a scroll message on a distant target.
Depending on the selected laser power and/or the size of the projected image, information can be written at night even on low hanging clouds. .
At least in theory.
Why the letter number?
Laser projectors popular in clubs or laser shows use galvos (
As an actuator instead of a measured galvonometer)
Or a quick two-mirror scanning device.
Mirror X galvo and mirror Y galvo corresponding to X and Y scans.
This allows the scanner to draw any 2D image on the screen.
The problem with Galvos is that they need a lot of labor to build and complex control.
The ready-made galvos are usually large and very expensive for simple portable projectors.
In addition, fast galvos is a power-hungry device that becomes prohibitive when operating from a handheld battery.
If you\'re just projecting alphanumeric symbols on the screen, I think that\'s excessive --
Simple tweets or text messages.
If you only need to display these, you can use a simpler method.
Align each fixed mirror at a slightly different angle relative to the projected surface can create a horizontal image on the screen that is sufficient to display numbers or letters.
You don\'t need to need too much power to run the motor like you do with two galvos, and the cost is much lower.
The obvious disadvantage of the scanning mirror method is that the vertical resolution is low because it is defined by the number of discrete mirrors.
However, high resolution is not important for alphanumeric projections.
The other less obvious is the total reflected power of the beam.
Whether the image is a single point or a solid rectangle, the intensity of the drawn image generated by rotating the mirror will be the same.
The mirror rotates at a constant speed and the laser is pulsed at the right moment.
Unlike galvos, the laser beam must \"wait\" until the rotary mirror reaches the correct angle before it can reach the correct position to flash again.
This waiting period is used as a duty cycle of the laser, which in turn limits the intensity of the reflected image.
In contrast, galvos forces the beam to track and re-track only the illuminated part of the image without wasting time scanning the projected area that is not related to the image.
If the image is small (e. g. single dot)
All the laser power is concentrated at that point.
As the size of the image increases, the intensity decreases proportionally (
Let\'s say the laser power remains unchanged).
Using a scanning mirror, the strength of the point is still a fraction of the total beam power defined by the duty cycle (
Turn on the laser to draw the duration of the point divided by the time it takes to make a rotation).
Therefore, the perceived brightness of a single point or set of points is the same as that of the observer.
Technically, the laser projection is not an image of a grating type, there is no \"pixel\" or point, but a tiny light vector, because the control mirror keeps moving the beam, so in theory you can\'t have a perfect point (a pixel).
But from now on I will call them pixels and they are more familiar anyway.
Details of the design motor rotary mirror drum rotate at least 25 rps or 1500 rpm (
25 frames per second).
Lower than this will produce visible flashes.
This is the typical motor type you find in CD, hard drive, floppy drive (
If you still have one).
Ideally it should be a low voltage motor.
The brushless motor lasts longer and runs quieter, but is not directly controlled like there is a brush DC type.
It doesn\'t need a lot of torque (like RC type).
I bought the old floppy drive, but the brushless motor for the CD/DVD drive is a better option.
Household rotary mirror drum
A designed scanning laser beam was made from 12 Rotary mirrors.
The design of this work is largely an exercise in geometry and patience.
To keep this simple, I am not going to use a focused optical device, which should be a small portable device.
Without focusing optics, there is almost no need to define constraints before constructing optics.
They are the size of the projected image, the distance of the projection and the intensity of the image (
This is related to image size and laser power).
If the goal is to project a short message at a very long distance, then the laser scanning angle must be very narrow and the image size is small (
Maybe a word or two)
In order to concentrate the maximum power on the target, because the strength is proportional to the projection surface.
For this case, I chose about 12ft of the image length at the distance opposite the room.
Each mirror on the drum is offset enough to produce a horizontal scan line just below the previous one during rotation.
The end result is to set the horizontal line on the screen that defines the height of the image (
Or the height of the alphanumeric symbol).
The easiest way I can think of is to align the mirror along the perimeter of the bottom of the drum and have some way to adjust the alignment angle.
The screw that sticks the nut to the drum is an idea, but it will work fine by rubbing the lock position, not the threaded screw.
The ideal mirror used is the front surface type (
The reflective coating is on the top surface of the glass, not behind the glass like most mirrors).
This minimizes distortion and power loss in the reflected beam.
The power of the semiconductor laser is limited, so do everything possible to reduce the power loss of the beam.
Front surface mirrors sold in hobby stores or ebay.
They are usually used in DIY kaleidoscope.
A thin mirror can be cut using a common glass cutter.
What I bought at Home Depot was the plastic base used to hold the mirror.
This is the paint cover for a large container.
The diameter is right ~ 2, also very suitable for installation on the rotor of the floppy drive motor.
The lip at the bottom is used to locate the mirror.
However, it wasn\'t until later that I realized that when I was sure it would be difficult to balance the drum even at low speeds, I should pay more attention to this step (
More will be introduced later).
Ideally this should be precision machined plastic, but it will be feasible for DIY.
If you have a 3D printer, this is the place to get you to work!
Each image in the component needs to be positioned at a specific offset angle relative to the previous image to create a projection line, just below the previous mirror line.
Silicone sealant is very effective, fixing only the bottom and a few points on the side of the mirror.
The cured silicone is hard enough to hold the position of the mirror, but flexible enough to fine tune the angle.
Using alignment screws, webcams, and TVs, I adjusted each mirror alignment angle to produce 12 vertical points at 0.
In ~ 5 \"distance of 10ft.
The final step is to connect the mirror to the drum using a 2 hour curing epoxy and ensure the safety of the calibration personnel.
To make this task easy to manage, I had to adjust and protect both mirrors at a time.
Good results.
The gap between mirrors is due to the fact that I am not very precise in cutting all mirrors.
I didn\'t bother to redo it because they were the way to pour glue and fix the mirror.
After installing the drum and rotating motor.
I got the green laser to shine the mirror to check the alignment of the horizontal line with the rotation of the drum.
I noticed that as RPM changes, the distance between scan lines drift occasionally, which brings alignment errors to mirrors with RPMs over 10 rev/sec.
At first, I suspect that the epoxy is not hard enough and that stretching can cause deformation and deformation of parallel lines.
But this idea is too far-fetched. . .
The introduction of this distortion is the vibration/resonance of unbalanced paint
Cover, homemade, epoxy sticky drum.
Drums need some fine tuning.
Balancing drums is hard to balance drums full of epoxy in all directions, but I find that most of the vibrations are side by side in my case. . . or seemed so.
The easiest way to adjust it is to add a metal washer to the top of the drum and use a strong nd magnet as the weight.
This is perfect.
Everyone knows that the bigger the laser power, the better.
If your laser can burn the whole object in concrete, just respect the eyes (if not yours)
There are other people.
The mirror will scan the laser beam in many directions, which can easily find the nearest eye.
Technically, the continuous power of the laser will never be concentrated at one point in this device, because the laser will always be pulsed.
Therefore, the average power on the projection surface will be less than the rated power of the laser.
According to the pulse rate, power can be estimated by: peak power * duty cycle = average power duty cycle determined by image size.
The larger the image, the longer the laser needs to wait.
Ignite the same pixelSo intensity (
Power/Image Area)
The image is proportional. I had to de-
To give our beam some radius, focus a little bit on the laser beam, which also reduces the intensity a little.
The ideal laser wavelength for laser display is about 532 nm.
This is a green beam.
The human eye has a variable sensitivity to the color spectrum of the light, and the green is the most sensitive.
Unfortunately, a semiconductor laser of this wavelength has not been produced so far.
Green laser diodes on the market use infrared pump LEDs and some frequency conversion crystals to produce green lasers.
I can\'t find small, reliable and affordable green lasers in my 50 s.
In addition to some suspicious sellers located on ebay overseas, 100 MW of electricity.
Most of their green laser diodes are self-made components with hot glue and pliers.
The laser diode I chose is Nichia ndb7875. This is 435-455nm (blue)laser.
Here is the datasheet: PDF file, although in theory you need more laser power to sense the same brightness as Green
This is a compromise.
This diode can be 1.
Stable light output power 6 W.
I \'ve heard that people run it to 2 w or even 2 at the absolute maximum rating of each data sheet. 1W.
The risk of damage laser operating at its absolute maximum rating without margin is high.
Environmental temperature changes, current spikes, and insufficient heat dissipation can all shorten the life of the diode and even destroy the diode.
But if you can afford it. often. . why not. . .
Since it\'s just a DIY, I want to push it to the edge and run at about 1. 8-2W.
The diode will dissipate close to 5-at this output power-6W of heat.
This is, however, a constant force.
In reality, the laser will be pulsed and will only dissipate part of it according to the duty cycle.
The specified operating temperature of this diode is only 0-
50C, reliable output.
While I don\'t have temperature monitoring or control like most lasers, I want to keep the laser below 50C without an oversized radiator.
This diode is a slightly larger 9mm case than the standard 5.
6mm will heat transfer a little better.
The worst case scenario is that if the space is limited to accommodate a suitable sized radiator, an idea to keep the laser temperature below 50C is to let the software dynamically change the duration of the pause (dark screen)
Between rolling messages and even sentences.
A duty cycle control.
You need some temperature feedback.
When the diode heats up, its forward voltage drop is reduced and the power consumed is reduced.
However, this effect may not help much when dealing with such a strict temperature range.
So the goal of the radiator without temperature feedback is to dissipate for 6 w long enough and keep the laser diode chip temperature below 50C, but allow the laser self-heating to remain above the minimum operating temperature.
The ambient operating temperature must be determined first.
For DIY prototypes, get something effective before reliability.
Therefore, the temperature stability and control are left on the laundry list.
Also, instead of working on a new radiator, I went to the radiator that was sold on ebay with a 9mm laser.
Beam divergence angle is an important factor affecting the quality of the lens.
There may be a variety of image differences using cheap lenses, and the worst is the optical power loss of the beam.
In addition, the lens must be able to withstand laser power without melting (
(If the laser power is high).
I chose single element 405-G-
2 shots can be found on ebay.
While I am not very happy with it, it has been claimed that it is the most effective in transmitting laser power compared to other devices.
On this, there is a lot of discussion on the type of lens to be used on the laser Forum: Ebay has a lot of sources for other laser accessories such as mounting brackets and two 4 radiators.
Laser diodes 5mm and 9mm.
Three circuits need to be designed outside the Arduino controller for electrical circuits: motor driver, motor speed/position detection, and laser modulation driver.
There is also a boost converter and several linear regulators to stabilize the voltage of the laser diode and motor and allow it to work from 3.
3 v lithium battery.