This article presents basic design ideas for laser virtual floor markers using inexpensive and readily available components...
The laser virtual floor marker introduced here is a specially developed portable laser beamer for the projection of abrasion-resistant virtual line markings on various floors. The compact laser beamer can be used to mark walkways, driveways, halt lines or danger zones easily even in very harsh environments. Different areas can be distinguished by different colors if necessary.
The key component of the laser beamer is a “line laser” which can often be found at retail outlets at discount prices. A line laser is a little device that employs a laser and an optical lens to project the laser beam as a line rather than a point. This may be attained by passing the beam through a cylindrical lens or a Powell lens. The picture below depicts a common 5-mW 650-nm line laser. The visible semiconductor lasers found in common laser toys too emit at about 650 ±20 nm and are generally in the Class IIIA Laser Product category, delivering less than 5 mW under DC bias conditions from 4.5 to 6 V.
Class 3A (IIIA) lasers are considered safe when handled carefully. There is only a small hazard potential for accidental exposure. It’s worth noting that the visible class 3R is similar to Class IIIA in the U.S. regulations.
You may check out this link to see a range of compact and affordable laser modules generating an accurate line (either a 58° or 88° full angle line, factory focused at 100 cm) at 635 nm or 650 nm with uniform intensity distribution.
Low-power laser diodes come in variety of packages. Generally, a laser diode emits light from both ends of its cavity, and most have a monitor photodiode integrated with the laser diode. The figure below shows a laser diode and monitor photodiode arrangement in can-style package. Check here for further reading.
This is the snip of a common low-power laser diode datasheet. Look up the highlighted segments. Note that Threshold Current (Ith) is the current at which lasing begins.
Since I came across several Chinese line lasers, I placed an order for a few. According to the seller’s description (look below) the device is tailored for 16- to 20-mA operation at 3 VDC, and I found that it has a built-in current limiting resistor. The only thing needed to drive the line laser is a 3-VDC power supply!
I rigged up a little “driver circuitry” for the line laser as I counted a distant possibility of subsequent design enhancements. Following is the first version schematic drawing of that line laser driver. As you can see, using a standard 555 timer IC it’s possible to create a simple line laser driver with a current drive capability up to 200 mA (maximum depends on supply voltage). The crude idea can also be modified to add pulse width modulation (PWM) drive capability, and a transistor output driver if used will raise the output drive (sink or source) capability by many folds.
We normally think of the 555 as a timer, but it is actually a very good pick for driving a small line laser. When pins 2 and 6 are taken to a voltage above 2/3 of the supply voltage, the output switches low (close to 0 V/GND), and if they are taken below 1/3 of the supply voltage, the output swings high (1.2 to 1.7 V lower than the supply voltage). Note that the standard (bipolar) 555 timer IC has a few characteristics that are unsuitable for battery powered circuits. It demands a minimum operating voltage of 5 V and relatively high quiescent supply current. During output transitions it produces current spikes of up to 100 mA, as well. The given circuitry has a “hard” on/off switch (S1), and the proposed power supply source is a standard USB power bank.
Also, the line laser diode (LD in the given schematic) can easily be controlled by a pulsed driver. Care should be taken to learn the electronic driver pulse signal before connecting the line laser because semiconductor laser diodes are prone to catastrophic failure due to transients (current glitches) in electronic pulser circuits. For longer pulse widths and with rise/fall times no shorter than 200 ns, the 555 timer IC can be used to directly drive a line laser diode at the nominal current level (circa 20 to 30 mA) with a current limiting series resistor. Again, make sure that drive spikes from the 555 chip are not excessive!
My quick lab experiment was on a mini breadboard assembly powered by a regulated 5-VDC source. Below you can see a couple of (wretched) snaps from my workbench. The 10-nF capacitor C3 has been left out on the breadboard.
If you look at the above lab snaps, you can see that the line laser part is somewhat different from the earlier web images. I do not want to keep the secret, so I will describe what I did there to save some money and time.
A while ago I found a listing of insanely cheap ($2) “laser taillights” online and I was curious as they’ve lasers to generate “laser bike lines.” Since I am always on the hunt for interesting things out of China, I bought it from a shop on web.
Amazingly, I found two encapsulated line laser modules (not well engineered though) inside the laser taillight. The laser line generator module has a red laser diode (with its series resistor) and the line generating optics wedged into a tight plastic tube.
I removed one laser module from the laser taillight and used in my breadboard prototype. A pair of red line laser modules plus some other useful (perhaps hackable) electronics for just $2 – that is why I bought it anyway.
The bike laser taillight runs on 3 VDC (1.5-V AAA cell x2) and I measured about 2.4 V across the microcontroller-driven line laser module in its “steady” mode (it also has a flashing mode). Since the estimated output of my design is 2.6 V, I simply wired the line laser module directly across the output points of my circuitry as depicted in the schematic. It worked right and there is no black smoke!
From night to morning!
It is easy to turn the basic circuitry into an automatic laser virtual floor marker with the help of a standard light dependent resistor (LDR). All you need is to wire a single LDR in parallel with the 10-uF capacitor (C4). If so, the circuit works only in the time between sunset and sunrise or when moved off into darkness.
The 5-mm LDR used in my breadboard assembly has a nighttime resistance greater than 75 KΩ and it is less than 2KΩ under normal daylight. So I stayed with the 10-KΩ resistor (R1), math showed me a resistance value of 12 KΩ though i.e. R1 = √ (2K x 75K) = 12.25 KΩ!
This is the quick breadboard test setup of the revised design. For the test, I (unintentionally) used another 5-mW red dot laser diode with a 43-Ω series resistor, and a GL5528 LDR. While testing, about 3.4 V is measured across the new red dot laser diode.
I unfortunately do not have a good enclosure to pack my laser beamer yet. But I have a bunch of cute ideas that look like this (thanks to https://www.lasershop.de).
Yes, it will work better than what I’ve already in my mind because it can be mounted on the ceiling or on the wall to beam a long laser routing line on the floor. I will try this later maybe in the next week.
The design has some inherent shortcomings, but overall, it is quite usable and does the intended job well. In a nutshell, this is a quick solution for a hobbyist to make a cheap and cheerful laser virtual floor marker at home. Hopefully, this will be useful in building more low-power and high-power visible laser projects in the future. Stay tuned for future ideas on how I will be utilizing this sparkling idea. Until then Happy Line Lasing!
This article was originally published at sister publication Electroschematics.