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Author Topic: Sub nano-second time measurement?  (Read 14667 times)
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Ichan
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« on: April 12, 2011, 06:15:58 18:15 »

A new Microchip application note AN1375-See What You Can Do with the CTMU, describe something about it:

Precision Time Measurement
Numerous applications require very precise time measurement. Using the edge trigger pins (CTEDn) on the CTMU, time can be measured precisely to a resolution of under a nanosecond. This is done by charging the A/D Sample-and-Hold (S/H) capacitor between the rising edges of the two pins; the resulting voltage is directly proportional to the time. Figure 5 shows the general scheme for time measurement. CTMU-based time  measurement is asynchronous to the clock running the microcontroller. Applications include:

15. Distance Measurement (Ultrasonic and Laser Devices)
The CTMU is used to measure the round-trip return time between an initial transmitted pulse and its reflected return signal. This can determine a distance measurement, accurate to within one foot.



Then a good laser range meter could be made from a cheap laser pointer. Workable? Prove it, will ya..?

Should this become a challenge or even a competition? Then it will be interesting  Grin

-ichan
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« Reply #1 on: April 13, 2011, 04:13:41 04:13 »

This was a big secret about 10 years ago. It was called "Micro Impulse Radar" and was used for sensing the level of material in a tank. Nobody but one guy was allowed access to the technology at the company I worked for. Search for "Micro Impulse Radar" or MIR. I know it cost a *lot* of money to license the technology.

The unit was an explosion-proof housing about 6 inches in diameter that held the electronics. A rod about 9 or 12 feet long came out of the bottom and made contact with the material you were trying to measure the depth of. The PIC "pinged" the rod with a short pulse. I never figured out if you were actually measuring the reflection of the ping or measuring the decay of the signal.
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solutions
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« Reply #2 on: April 13, 2011, 08:09:00 08:09 »

One of the biggest challenges in this "theoretical" method is going to be repeatability.  The assumption is that there is no electrical noise, no clock jitter, no cap leakage, perfect s/h switches, and in the case of the laser pointer that you can gate the light beam on and off abruptly enough and repeatably.

I'm skeptical that this is much more than marketing hype, or naivete by "designers" who won't stand behind their assertions with a reference design (they are very careful to wash their hands that any of this works...."just ideas").
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Jehan
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« Reply #3 on: April 14, 2011, 05:23:06 17:23 »

Laser Time of flight measurement will require 10s of picosecond resolution to get an accuracy of around 1 cm, with one nanosecond accuracy we can get around a .33 meter accuracy
nice thought to built laser range meter with just pic , a laser pointer and a photodiode.
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Tanuki
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« Reply #4 on: May 09, 2011, 10:51:25 22:51 »

This company has a number of different time-to-digital converters. Data sheets, application notes and sample/evaluation software too! LIDAR is one of their primary applications.

http://www.acam.de/products/time-to-digital-converters/
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DreamCat
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« Reply #5 on: May 13, 2011, 06:51:16 06:51 »

it need nano-second level response speed.. which PIC chip can do it?

TDC-GP2 is not chip, about 100 yuan in our country.
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May be I expressed the wrong meaning, sorry for my bad english. Please correct it for me if you can.
solutions
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« Reply #6 on: May 13, 2011, 08:11:32 08:11 »

I have a book request in this thread that has a section on time of flight - hopefully someone will have it and post it for us

http://www.sonsivri.com/forum/index.php?topic=20780.new#new
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Ichan
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« Reply #7 on: May 23, 2011, 11:02:14 23:02 »

Funny that the app note is not exist any more on the microchip web-site..

I just got my pic with ctmu and they withdraw tha app not, huh?

-ichan
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PCROBOTICS
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« Reply #8 on: May 24, 2011, 05:53:28 05:53 »

Funny that the app note is not exist any more on the microchip web-site..

I just got my pic with ctmu and they withdraw tha app not, huh?

-ichan

i do not know happened, but I did find the application note on the microchip website.

http://ww1.microchip.com/downloads/en/AppNotes/01375a.pdf
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Ichan
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« Reply #9 on: May 24, 2011, 04:08:39 16:08 »

Thanks, how did you found it?

I can not find it by browsing the app note list also by searching AN1375 or ctmu.

-ichan
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« Reply #10 on: May 26, 2011, 06:20:26 06:20 »

Thanks, how did you found it?

I can not find it by browsing the app note list also by searching AN1375 or ctmu.

-ichan

Smiley Many times the search engine companies such as microchip not help me, so I opted for Mr. Google. See attached image...  Cheesy

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