Time of Flight Laser Project

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  • Laser DeveloperLaser Developer Posts: 140
    edited 2012-01-23 - 04:34:18
    The first draft of the manual for the laser range finder can be found here. Sorry about the large file size.

    http://www.lightware.co.za/download/doc/DS00 - Laser Range Finder Manual_Rev_00.pdf

    Please comment if you find errors or think that more explanation is needed. Thanks.
    Detect and measure
  • jmgjmg Posts: 12,881
    edited 2012-02-05 - 12:29:12
    I'm trying to find the thread, but someone in the last few months posted work using TWO props, to do sub-ns timing.
    Like the "random dither" mentioned here, this used multiple sampling, and the fact the two clocks are NOT phase-locked.
    In the simplest form, two Props may not be needed, it may be OK to run two carefully decoupled Oscillators.

    Found it:
    http://forums.parallax.com/showthread.php?135563-Measure-the-speed-of-electricity.../page2&highlight=measure+wire+speed

    Best I can find is : "it appears able to have about 50 picoSecond resolution.", but not confirmed.

    It should be possible to predict the average-number needed, and the time precision, from the signal difference ?
    These systems will need a lot of averaged-reading to give stable results.
  • RacetrackRacetrack Posts: 2
    edited 2012-02-17 - 12:01:15
    The first draft of the manual for the laser range finder can be found here. Sorry about the large file size.

    http://www.lightware.co.za/download/doc/DS00 - Laser Range Finder Manual_Rev_00.pdf

    Please comment if you find errors or think that more explanation is needed. Thanks.

    A quick question; what is the function of the "APD bias switch" signal and the associated NC7SZ125 circuit in the receiver module (page 9)?
  • Laser DeveloperLaser Developer Posts: 140
    edited 2012-02-18 - 03:55:08
    what is the function of the "APD bias switch"

    Thanks for the question, Racetrack.

    In order to optimize the APD bias voltage, the amount of noise generated by the APD must be measured. When the APD bias is below a critical breakdown voltage, there is zero noise and when it is above the breakdown voltage the amount of noise rises rapidly. Ideally, we woud like to measure the return signal under zero noise conditions, but for the automatic APD bias control loop to work properly (stable, linear control response), there needs to be some noise present. The bias switch raises the APD bias voltage for a short period causing a burst of noise to show up on the return signal, even when the bias voltage is operating below the breakdown point. The noise counter runs during the time that the bias switch is on but is off the rest of the time. In contrast, there is no activity on the laser and no return signals present when the APD bias switch turns on.

    In summary, the APD bias switch alows the measurement of distance to be done under zero noise conditions when the bias voltage is just below breakdown, whilst the control loop for the bias voltage uses data taken just above the breakdown voltage. When looking on the testpoints you can see the "quiet" period when the laser is firing and the return signal is being measured, then there is a burst of noise as the bias switch turns on and the noise counter starts to run and the APD bias control loop does its thing.

    I think that it's features like this one that sets the DS00VQ100 chip apart from other "timer" chips like those from ACAM. The DS00VQ100 is actually a complete TOF LRF system controller, not just a high speed timer. This means that the design of an LRF is much simpler than it would otherwise be if every function was created by separate devices. As a further example of a system level function, there is a synchronous, high voltage controller on the DS00VQ100 that is not used in the DS00 design but works with non-hybrid lasers that need a high firing voltage.

    DS00 demo kit ready for shipping:

    photo.JPG
    555 x 469 - 90K
    Detect and measure
  • RacetrackRacetrack Posts: 2
    edited 2012-02-19 - 20:45:38
    That's very nifty. May I ask why you did not simply go for a thermistor controlled bias supply? Assuming the latter is properly calibrated, how would you compare the two methods (pros/cons)? Reasons for asking is I'm fairly new to these devices, and I'm trying to get some insight.
  • Laser DeveloperLaser Developer Posts: 140
    edited 2012-02-19 - 22:01:37
    Racetrack wrote: »
    why you did not simply go for a thermistor controlled bias supply?

    A thermistor control does not take into account changes in the background light leakage through the optical filter. Even though this is a small amount of energy, it becomes the dominant source of noise when operating at the bias voltage breakdown limit.

    By measuring the APD noise directly rather than trying to measure the causes of the noise (temperature, background light, radiation, power supply ripple, amplifier noise, EMI etc) you can make a much more precise control loop which is able to hold the APD at the optimum gain/noise bias voltage. In addition, it is not necessary to manually calibrate the temperature profile of each individual APD and it is not necessary to compensate for variations in the supply voltage to the HV bias generator.

    In contrast, something like a thermistor control can only monitor the weak relationship between APD noise and temperature. This is fine for a system where conditions are stable or where the optimum performance is not necessary. But if your LRF is to work over a wide temperature range and in bright/dark conditions, then keeping the APD gain above 100 becomes difficult using only a thermistor.

    There is a caveat to this explanation, which is that most timing circuits can't tollerate ANY noise on the return signal. This is because noise is interpreted as a valid return signal which stops the timer. In these systems, the APD bias is kept well below the breakdown voltage. However, the DS00VQ100 chip is extremely noise tollerant because it has built-in digital filtering. This means that the APD can be run at a much higher bias voltage than in other systems, giving the LRF longer measuring range even with inferior optics and low cost amplifiers.
    Detect and measure
  • prof_brainoprof_braino Posts: 4,312
    edited 2012-02-23 - 14:27:08
    Re: posts 186, 188:

    This is a very nice explanation. Generally, if one person asks, many other will have the same question. Could the answer above be added to the data sheet, as a footnote or such?
  • Laser DeveloperLaser Developer Posts: 140
    edited 2012-02-23 - 22:59:07
    Thanks for the feedback Prof - will expand the section on APD noise control in the next revision of the DS00 Product Manual. I'm not sure if the document is easy to read or if it already contains way too much information. I could add another twenty pages of explanation without covering all the possibilities... :smile:

    For those who haven't seen the document it can be found here:

    http://www.lightware.co.za/download/doc/DS00%20-%20Laser%20Range%20Finder%20Manual_Rev_00.pdf

    Any feedback would be welcome.
    Detect and measure
  • prof_brainoprof_braino Posts: 4,312
    edited 2012-03-06 - 08:59:44
  • Laser DeveloperLaser Developer Posts: 140
    edited 2012-03-27 - 15:36:34
    There is an updated version of the DS00VQ100 datasheet available on the www.lightware.co.za website.

    This is a major update to the information with more detailed explanations about how the chip works. In addition there are a few new features including:

    - a latch for the external data signals
    - an EEPROM interface for storing calibration data
    - dedicated expanded timebase signal outputs

    Many thanks to Prof Braino for his help in editing the document!
    Detect and measure
  • speedbusterspeedbuster Posts: 1
    edited 2012-07-14 - 23:52:38
    We are a very small group in the traffic safety domain. We want to develop a Laser speed meter. Looking for laser controllers and drivers along with optics. Any help would be appreciated
  • FranklinFranklin Posts: 4,747
    edited 2012-07-15 - 19:24:51
    Looking for laser controllers and drivers along with optics. Any help would be appreciated
    So, what did you find in this thread that you can use and what do you still need to accomplish? There are laser speed meters on the market, what is it they don't do that you need? You really should open your own post with your question.
  • prof_brainoprof_braino Posts: 4,312
    edited 2012-07-16 - 08:47:16
    We are a very small group in the traffic safety domain. We want to develop a Laser speed meter. Looking for laser controllers and drivers along with optics. Any help would be appreciated

    Hello speedbuster! Welcome to the forums!

    Ok, willing to help. What are your questions?

    You can post here, open a new thread, send private messages to me, or any other option you choose.
  • farmflyfarmfly Posts: 1
    edited 2013-03-24 - 06:25:20
    I want one.
    Am into rc planes and GPS altitude fine for that. More suitable for uav and possibly fpv market.
    Configure for longer range put led pointer on it and sight scope with distance readout and you have a great long distance electronic tape measure. Link with android phone to configure and results.
    Maybe set distance with dial then have output if something in range. (ground for uav)
    I see so many possibilities for this . Especially so configurable.
    Surveyors,miners, builders then uav and hobby market.
    Boomspray 400000$ Machine 120 feet wide 30km/hrs often at night early warning system for trees. Am I going to hit that buzzer goes off you are too close.
    ALOT of work and thought went into this and it would be a shame if it stalled at this late stage.
  • prof_brainoprof_braino Posts: 4,312
    edited 2013-03-26 - 15:14:43
    I believe you can order them for personal use directly from www.lightware.co.za website.

    Because of restrictions on the laser and costs of paperwork, I couldn't import them for resale, but there is nothing to stop an individual from ordering directly. I don't know how many are still available. The first run were snapped up very quickly.
  • I know this is an old post, a verrrry old post, but I am trying to find someone who has ready made boards, or knows where I can get them made for the SPL LL850nm pulsed laser diode using the same design. If you do, please contact me.
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