Putting A Cheap Laser Rangefinder Through Its Paces | Hackaday

2022-10-20 20:55:32 By : Ms. Bella Xiao

Sometimes a gizmo seems too cheap to be true. You know there’s just no way it’ll work as advertised — but sometimes it’s fun to find out. Thankfully, if that gadget happens to be a MILESEEY PF210 Hunting Laser Rangefinder, [Phil] has got you covered. He recently got his hands on one (for less than 100 euros, which is wild for a laser rangefinder) and decided to see just how useful it actually was.

The instrument in question measures distances via the time-of-flight method; it bounces a laser pulse off of some distant (or not-so-distant) object and measures how long the pulse takes to return. Using the speed of light, it can calculate the distance the pulse has traveled). High Accuracy Laser Distance Sensor

Putting A Cheap Laser Rangefinder Through Its Paces | Hackaday

As it turns out, it worked surprisingly well. [Phil] decided to focus his analysis on accuracy and precision, arguably the most important features you’d look for while purchasing such an instrument. We won’t get into the statistical nitty-gritty here, but suffice it to say that [Phil] did his homework. To evaluate the instrument’s precision, he took ten measurements against each of ten different targets of various ranges between 2.9 m and 800 m. He found that it was incredibly precise (almost perfectly repeatable) at low distances, and still pretty darn good way out at 800 m (±1 m repeatability).

To test the accuracy, he took a series of measurements and compared them against their known values (pretty straightforward, right?). He found that the instrument was accurate to within a maximum of 3% (but was usually even better than that).

While this may not be groundbreaking science, it’s really nice to be reminded that sometimes a cheap instrument will do the job, and we love that there are dedicated folks like [Phil] out there who are willing to put the time in to prove it.

I have an Opti-Logic 120 XL and my only complaint has been with having to remove the rubberized coating with alcohol because over time it becomes a horrible tacky black goo mess.

I started out measuring against it with a 300 foot tape measure to make sure it was accurate, while using it with my clinometer to measure tree height, and then measuring the tree length after I cut down the tree to double check both results. It probably ends up being more accurate then using a physical tape measure, especially at 100+ foot distances because you do not add or lose distance because of uneven ground or tape slack going to the tree trunk.

It has been a very useful and time saving tool because on long runs you either need another person or 20# of rock or brick to hold the loose end of the reel. Plus, you do not need to reel out and then reel in 200+ foot of tape. I now trust the results from the range finder more then I do the tape now,

As Reagan pointed out “trust, but, verify” first before you go MAD.

That’s a bit radical, cutting down trees just to validate an instrument… ;-)

For old rubber coatings that have become tacky, you can apply some talc powder or baby powder for a non permanent fix.

Thank you, I will keep that in mind, as I have come across vehicle steering wheels with the same problem. Though I removed it all with rubbing alcohol down to the plastic for a permanent solution on the range finder.

Laser rangefinders (in the form of parallax ones though) have been a cheaply solved problem for so long Canon made one of their first autofocus systems by just slapping one into every lens.

Yeah, they’ve been in cameras for decades and laser measuring tapes at the hardware store for at least one, and while they started at $200 in the early noughties, they are what $30 or $40 now. … and I’m sure it takes better, tighter tolerance tech to measure stuff a few feet away than a few hundred feet (But maybe a higher power diode laser, which have come down in price and gone up in availability)

A parallax meter doesn’t usually work very well beyond 10 meters or so.

Getting a range finder for less than 100 euros isn’t exactly “wild” (Well, maybe it is in Europe). MidwayUSA has several models available in that price range. Of course from there they go up. Way up…

What he doesn’t mention is that the device reports distances rounded to 0.1m. Thus due to that you’d expect rounding errors of up to 0.1m / 3m = 3.3% at the low end of the range.

I saw a +/- 0.01 digit somewhere. That’s obviously a wrong claim: It means that if the readout is 123, (ending at the 3), then the device would be accurate to 0.01, i.e. a real value of 123.45 would be displayed as 123.44 to 123.46 at the extremes….. Cannot be true.

a lot of the low-cost laser rangers don’t directly measure time of flight based on a laser pulse. Instead they modulate the laser and measure the phase between the outgoing and return beams. The timing requirements are much simpler.

That’s pretty much how those cheap microwave radar modules do it too I recall.

it’s how Apollo missions did ranging too. I’d almost argue for calling that method “Modulated TOF” as compared to “Pulsed TOF”. so it is still a ToF

Yes, you are right about cheap laser tape measures (with max 150 m range) – they are using phase method for distance calculation. Cheap “Golf” laser rangefinders with range 400-1500 m are based on “true” pulsed time-of-flight. Using pulsed method, you can use laser with a big power, which is really important at long distances.

File it under: Product review that has nothing to do with hardware hacking.

This is a bit more than an ordinary unboxing or review. Analysis of things is the first step into deciding if something is worth hacking or perhaps usable in another hack of some kind.

Are there any known life time issues with this sort of thing? For example lasers that die prematurely because they are overdriven? or lenses that are mounted so badly they may loose alignment if you look at them crookedly?

I would assume not. The lenses are probably mounted in such a way that when the two haves of the body are pressed together they are squeezed in to their mounting points so they can’t move unless the screws are loosened. As for the laser, if it’s pulsed you could probably overdrive it so long as the pulse width is shorter than what is needed to begin heating the emitter. My guess however is this laser (and pretty much all lasers used in a way you might point them at a person’s eyes) is probably well under it’s max driving current/voltage simply due to max output regulations. In pulsed mode, laser diodes tend to last significantly longer than not pulsed, even if they are overdriven a little.

Beyond all that I’ve certainly never heard of a wave of horribly broken range finders hitting the market.

Can you get something similar at Harbor Freight?

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Putting A Cheap Laser Rangefinder Through Its Paces | Hackaday

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