4 ms·

Laser distance meters have been available to contractors for years. The major difference Senic adds, over Ryobi, Bosch & Fluke, is bluetooth & cloud syncing. I

Laser distance meters have been available to contractors for years. The major difference Senic adds, over Ryobi, Bosch & Fluke, is bluetooth & cloud syncing. I have always wondered how these devices actually calculate distances. I have experimented with Arduino & Parallax, and I've seen how the resolution of an ultrasonic distance sensor is directly affected by the processor speed -- the processor is merely counting the fractions of a second between sending the ping pulse, and receiving its echo. But a 1 MHz processor can only just count milliseconds. A 16 MHz processor can count only slightly faster. At the room-temperature speed of sound, this gives you a resolution of about 1/29th of an inch, or 1/74th of a centimeter. In theory, the same should be possible with light -- send a light pulse then count the fractions of a second for it to return. Thinking back to Grace Hopper's Nanosecond [1], a 1mhz processor would have a resolution of hundreds of feet. So these must be using a very small, simple, multi-GHz processor to get a resolution of about 2/15 of an inch. Unless these devices do their measurement in a completely different way... [1] https://www.youtube.com/watch?v=JEpsKnWZrJ8 https://www.youtube.com/watch?v=JEpsKnWZrJ8

Retric 13y ago
You don't need a full processor for time of flight just a few transistors which can cheaply operate at ~10GHz. Speed of light / 10ghz = 3cm, but your talking round trip timings so ~1.5 cm is possible. Multiple frequency phase-shift or Interferometry allows you to do even better.
- stephengillie 13y ago
  Very good point -- you'd have these fast, expensive transistors (however they are packaged or not packaged) cache their data, then transfer it back to a slower, cheaper, main microprocessor, which would be doing the rest of the device's work. Do you know where these 10 GHz transistors can be found?
  - beambot 13y ago
    Laser rangefinders don't switch the light source at 10GHz. They "chop" the laser on-off at (say) 10kHz. The measure the difference between the reference (onboard) and the return using (typically) a PLL that can measure time differences down to picoseconds (these are usually used in high-frequency RF equipment). Using a microcontroller counter would be too slow. Cheaper LRF's can use triangulation with a known baseline. That's how Neato robotic managed their $10 spinning version for the vacuum: http://www.hizook.com/blog/2009/12/20/ultra-low-cost-laser-rangefinders-actualized-neato-robotics http://www.hizook.com/blog/2009/12/20/ultra-low-cost-laser-r... To wit... I like to disassemble laser rangefinders! http://www.hizook.com/blog/2009/01/04/velodyne-hdl-64e-laser-rangefinder-lidar-pseudo-disassembled http://www.hizook.com/blog/2009/01/04/velodyne-hdl-64e-laser... http://www.hizook.com/blog/2009/02/14/omron-sti-optoshield-os3100-laser-rangefinder-lidar-disassembled http://www.hizook.com/blog/2009/02/14/omron-sti-optoshield-o... http://www.hizook.com/blog/2008/12/15/sick-laser-rangefinder-lidar-disassembled http://www.hizook.com/blog/2008/12/15/sick-laser-rangefinder...
    - stephengillie 13y ago
      Wow, amazing!
- jacquesm 13y ago
  It gets much more precise than that, it's the phase that matters not the time. Laser interferometers routinely measure microns. http://en.wikipedia.org/wiki/Interferometry http://en.wikipedia.org/wiki/Interferometry If they're not going for that kind of precision and range they could simply use ultrasound instead of a laser. Range on this thing is impressive and precision is too: accurate up to 0.075 ", though they don't specify at what range that precision is still attainable. Typically with increased range on cheap devices you'll get an increase in absolute error so a percentage of the absolute distance would be expected. Maybe that's due to this being a laser device. Interesting application of tech, a bluetooth enabled range finder could really be useful, especially for realtors that have to measure up a whole bunch of houses on a typical day and that need to keep track of what they measured. Even more useful if the app would record audio along with the measurements made for later transcription.
abthomson 13y ago
For shorter distances, time-of-flight is not typically used. There's surprisingly little documentation about how these things work online though. From http://ptd.leica-geosystems.com/en/Measuring-Techniques_4939.htm http://ptd.leica-geosystems.com/en/Measuring-Techniques_4939... "The laser diode emits light pulses with a defined wavelength and pulse repetition frequency. Due to the runtime difference between the internal reference path and the external measurement path, the light pulses, reflected on a target and received from the Leica DISTO™, have experienced a phase shift in relation to the light pulses received through the internal reference path. That phase difference between those two signals is proportional to the distance between instrument and target."
ohazi 13y ago
These devices do their measurement in a completely different way. Laser distance meters are essentially tiny radar units operating with light instead of radio waves (lidar). With a pulse radar, you need the pulse itself to be of extremely short duration, especially when you're measuring short distances. You need to have stopped transmitting by the time you begin receiving the reflection to have any hope of actually finding the reflection (because the return "sounds" exactly like what you're transmitting). In order to reliably detect a short unmodulated pulse, the transmitted power generally has to be pretty high so that the reflection is loud enough that you don't miss it. Short pulses and high power are generally hard to do with cheap semiconductor devices (big radar pulse generators tend to use vacuum tubes and exotic and expensive hardware). A better approach for lower power devices is to modulate the carrier wave itself and then transmit a longer, lower power pulse. One way to do this is to transmit a "chirp" (a transmission that starts at a low frequency and ramps up to a high frequency). When you receive the radar return, you'll start receiving the initial low frequency while the transmitter has moved on to transmitting a higher frequency. You can then use this frequency difference and the chirp rate to compute the time of flight and therefore the distance. This also has an added advantage of allowing you to integrate the received signal for a much longer period of time, so it tends to be a lot less noisy and error prone than a pulse radar. [1] http://en.wikipedia.org/wiki/FMCW#Modulated_continuous-wave http://en.wikipedia.org/wiki/FMCW#Modulated_continuous-wave

Retric 13y ago

You don't need a full processor for time of flight just a few transistors which can cheaply operate at ~10GHz. Speed of light / 10ghz = 3cm, but your talking round trip timings so ~1.5 cm is possible. Multiple frequency phase-shift or Interferometry allows you to do even better.

stephengillie 13y ago
Very good point -- you'd have these fast, expensive transistors (however they are packaged or not packaged) cache their data, then transfer it back to a slower, cheaper, main microprocessor, which would be doing the rest of the device's work. Do you know where these 10 GHz transistors can be found?
- beambot 13y ago
  Laser rangefinders don't switch the light source at 10GHz. They "chop" the laser on-off at (say) 10kHz. The measure the difference between the reference (onboard) and the return using (typically) a PLL that can measure time differences down to picoseconds (these are usually used in high-frequency RF equipment). Using a microcontroller counter would be too slow. Cheaper LRF's can use triangulation with a known baseline. That's how Neato robotic managed their $10 spinning version for the vacuum: http://www.hizook.com/blog/2009/12/20/ultra-low-cost-laser-rangefinders-actualized-neato-robotics http://www.hizook.com/blog/2009/12/20/ultra-low-cost-laser-r... To wit... I like to disassemble laser rangefinders! http://www.hizook.com/blog/2009/01/04/velodyne-hdl-64e-laser-rangefinder-lidar-pseudo-disassembled http://www.hizook.com/blog/2009/01/04/velodyne-hdl-64e-laser... http://www.hizook.com/blog/2009/02/14/omron-sti-optoshield-os3100-laser-rangefinder-lidar-disassembled http://www.hizook.com/blog/2009/02/14/omron-sti-optoshield-o... http://www.hizook.com/blog/2008/12/15/sick-laser-rangefinder-lidar-disassembled http://www.hizook.com/blog/2008/12/15/sick-laser-rangefinder...
  - stephengillie 13y ago
    Wow, amazing!
jacquesm 13y ago
It gets much more precise than that, it's the phase that matters not the time. Laser interferometers routinely measure microns. http://en.wikipedia.org/wiki/Interferometry http://en.wikipedia.org/wiki/Interferometry If they're not going for that kind of precision and range they could simply use ultrasound instead of a laser. Range on this thing is impressive and precision is too: accurate up to 0.075 ", though they don't specify at what range that precision is still attainable. Typically with increased range on cheap devices you'll get an increase in absolute error so a percentage of the absolute distance would be expected. Maybe that's due to this being a laser device. Interesting application of tech, a bluetooth enabled range finder could really be useful, especially for realtors that have to measure up a whole bunch of houses on a typical day and that need to keep track of what they measured. Even more useful if the app would record audio along with the measurements made for later transcription.

abthomson 13y ago

For shorter distances, time-of-flight is not typically used. There's surprisingly little documentation about how these things work online though. From http://ptd.leica-geosystems.com/en/Measuring-Techniques_4939.htm http://ptd.leica-geosystems.com/en/Measuring-Techniques_4939... "The laser diode emits light pulses with a defined wavelength and pulse repetition frequency. Due to the runtime difference between the internal reference path and the external measurement path, the light pulses, reflected on a target and received from the Leica DISTO™, have experienced a phase shift in relation to the light pulses received through the internal reference path. That phase difference between those two signals is proportional to the distance between instrument and target."

ohazi 13y ago

These devices do their measurement in a completely different way. Laser distance meters are essentially tiny radar units operating with light instead of radio waves (lidar). With a pulse radar, you need the pulse itself to be of extremely short duration, especially when you're measuring short distances. You need to have stopped transmitting by the time you begin receiving the reflection to have any hope of actually finding the reflection (because the return "sounds" exactly like what you're transmitting). In order to reliably detect a short unmodulated pulse, the transmitted power generally has to be pretty high so that the reflection is loud enough that you don't miss it. Short pulses and high power are generally hard to do with cheap semiconductor devices (big radar pulse generators tend to use vacuum tubes and exotic and expensive hardware). A better approach for lower power devices is to modulate the carrier wave itself and then transmit a longer, lower power pulse. One way to do this is to transmit a "chirp" (a transmission that starts at a low frequency and ramps up to a high frequency). When you receive the radar return, you'll start receiving the initial low frequency while the transmitter has moved on to transmitting a higher frequency. You can then use this frequency difference and the chirp rate to compute the time of flight and therefore the distance. This also has an added advantage of allowing you to integrate the received signal for a much longer period of time, so it tends to be a lot less noisy and error prone than a pulse radar. [1] http://en.wikipedia.org/wiki/FMCW#Modulated_continuous-wave http://en.wikipedia.org/wiki/FMCW#Modulated_continuous-wave