Laser altimeter - new design

Hi to everyone at DIY Drones!

I don't know much about UAVs, my specialization is the design of laser products. I recently made a laser range finder by accident that might be useful in UAVs.

It started out as a project to design a new kind of chip that can measure events happening at the speed of light. Then, in order to prove that the chip worked properly, I had to make a test bed which turned into a laser range finder.

The chip has programmable performance settings so it can be used for either long range, high resolution or fast update rate measurements or some combination of these factors although not all at the same time. There is no minimum range, it works down to zero meters.

The best programmable settings give:

Best range >100m (to trees and grass)

Best resolution 1cm

Best update rate 100 readings per second 

You can see from the attachment that the range finder is quite small. The optics are made from acrylic so the whole thing is very light weight. It has an SPI connection to a host processor or it can have one already attached like in the picture. The laser is Class 1M. The optics are separate from the electronics so that they can be scanned with a servo or mounted on gimbals. It runs from 4.5V to 7.2V batteries and draws less than 200mA.

At the moment I'm looking to see if there is a market for something like this. I might consider producing small quantities for around $450. I'm not based in the USA so there are no export restrictions.

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Permalink Reply by Laser Developer on January 14, 2012 at 10:43pm

The main differences are:

  1. The accuracy is better (LRF = 1cm; opti-logic = 1m)
  2. The resolution is better (LRF = 1cm; opti-logic = 20cm)
  3. Minimum range is better (LRF = 0m; opti-logic = 4m)
  4. Calibrated update rate is better (LRF = 100Hz; opti-logic = 10Hz)
  5. Power consumption is lower (LRF = 0.8W; opti-logic = 1.8W)

Opti-logic has a version that will measure longer range.

Permalink Reply by Laser Developer on January 14, 2012 at 10:36pm

Address sent by private message.

Permalink Reply by malcolm churn on January 18, 2012 at 4:58am

Looks good to me...255g is no problem for my heli to lift.

Permalink Reply by vladimir.d.makarov on February 6, 2012 at 12:31pm

Laser Developer,

 

This looks really cool and at $450 it is reaching a point where it can be used for hoppy/amateur applications.

 

Is this laser rangefinder based on the triangulation or time of flight techniques?

 

Permalink Reply by Laser Developer on February 6, 2012 at 11:35pm

Hi Vladimir,

Thanks for your feedback. This is a time-of-flight laser, triangulation devices are limited to a range of a few meters.

The key to long range performance, high resolution and relatively low cost is the timer chip - DS00VQ100. This chip handles all the range finding functions including firing the laser, controlling the high voltage bias on the APD detector, doing the timing and correcting for electronic delays. You can see it on the timer board below. The DS00VQ100 will be available for sale to the public sometime in the next few months at about $35 a piece.

You can find a detailed explanation of how the laser range finder works here:

http://www.lightware.co.za/download/doc/DS00%20-%20Laser%20Range%20...

Permalink Reply by Cliff Gill on February 7, 2012 at 7:35am

Would you have an option for a longer range device? Like 1000 meters or so?

Permalink Reply by Laser Developer on February 7, 2012 at 7:48am

Cliff, the technology for longer ranges is a bit different. Usually the resolution and short range capability are compromised and a laser with higher peak power and precision optics is used. The technology behind long range LRFs is well understood and they are used in many military range finders but I don't make these kinds of instruments. 

Permalink Reply by vladimir.d.makarov on February 7, 2012 at 2:58pm

Cliff,

Why would you need range of 1000m? 100m seems plenty for DIY-drone applications....?

 

Laser Developer,

Wow, the documentation you provided is excellent, explains how laser rangefinding works. This technology is very interesting.

Couple of more questions:

1) Could this be turned into a simple LIDAR system by attaching it to a motor and having the sensor/laser scan a plane?

2) Can the system you are offering be purchased in a manner that makes it slightly cheaper?? I am thinking a kit of components that one has to solder themself or maybe replace some of the expensive components with lower quality ones?? While I think the rangefinder is a great value for $450, it would be more accessible to the hobby market if it was more in the $100-200 range (at least that's what my budget would allow).

3) I have a EE degree, and am involved in work with lasers, but not really rangefinding. So all of this stuff is very interesting to me. What is toughest part of building a system like this? Let's say I was going to build this with a laser pointer and photodiode, what would be the difficult part of building something like this in my basement?

 

Super interesting stuff, thanks for posting this!

 

Permalink Reply by Laser Developer on February 8, 2012 at 3:25am

Glad you like the manual Vladimir.

1) Yes. The optics have been made separate from the electronics so that they can be scanned using a servo.

2) I think that it is important to make the LRF available to as many people as possible, so I will sell whatever people want to buy - finished kit, parts, specialized components or just the timer chip. Most of the cost goes into a few components like the laser, the APD detector, the optical filter etc. I will try to put as much of the design on the Internet as possible so that people have enough information to select alternative parts.

3) It would be great to see someone else put together an LRF, it's quite a challenge. The most difficult aspect of the design is the total system complexity - optical design; high speed, low noise circuit layout; you might have to design your own chips; write software; mechanical design etc. But if you break it down into small steps then it can definitely be done.

Using a low cost, laser pointer the easiest LRF to make is based on triangulation. There are many examples of this on the Internet but it only has a useable range of a few meters.

For longer range measurements you can use FMCW - Frequency Modulated, Continuous Wave. Unfortunately, it is very hard to find detailed designs for this technology. If you are good at RF design then this would be a natural approach to use but most products that use this technique have custom made chips to modulate the laser and demodulate the return signal.

Time-of-flight design is best done with a high power, pulsed laser rather than a laser pointer. I like the SPL-LL85 from Osram - it is very easy to work with and a good price. It is possible to keep the cost of the LRF down by using a PIN diode rather than an APD and not using an optical filter. This reduces the measuring range but it is a relatively simple design if you use the DS00VQ100 or an ACAM timer chip to handle the timing.

Permalink Reply by Tomas Soedergren on February 8, 2012 at 4:39am

Hi Laser,

VERY intereting gadget, and IMHO a candidate for upgrade/ replacing the (not so easy and reliable) sonar system we use today on the ArduCopters. The cost is much higher, but some of us would be prepared to pay if it offers new level of altitude control performance.

Three questions:

  1. Will it work reliably over water?
  2. How temperature sensitive is it (I live in Scandinavia, temps between +30 and -25C)?
  3. Does it have internal signal processing to handle situations like light snowfall?

/ Tomas

Permalink Reply by Laser Developer on February 8, 2012 at 5:18am

Hi Thomas, thanks for your interest.

1. In many cases the LRF will measure water like dams and rivers. In some cases, if the water is very clear or very still it may lose signal.

2. I have not tested this LRF design in cold conditions but my past experience tells me that lasers work well at low temperatures. The speed of light is not affected by air temperature.

3. There is filtering built into the timer chip that removes noise and unwanted signals. I would expect that as long as the surface to be measured can easily be seen then the laser should be able to measure correctly. There are settings that can be adjusted to improve noise rejection and there is also the possibility of adding smoothing software to post-process the results. A simple filter that removes short readings but keeps the longest ones works well.

Cool questions!

Permalink Reply by Cliff Gill on February 8, 2012 at 6:47am

Vladimir, I would like a longer range version for manned applications.

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