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Topic: Time of flight module (Read 962 times) previous topic - next topic

Ma7moud

Even if a TOF radio module were available for Arduino, how would that help to measure the time taken from an Android phone (or other device) ?

To use TOF to measure distance from the Android phone you would need to know within a few hundred nS exactly when the signal was sent.
Simply, the ToF-enabled device send a challenge to the other device. The other device has to respond to this challenge as fast as possible (In other words, the processing time should be a very small fraction to neglect it). Once the response arrive the ToF-enabled device, it can measure the time needed for that signal to arrive by calculating the propagation delay through dividing the ToF by 2. Other aspects have to be taken into account, but this is the idea in simple way.

Grumpy_Mike

Simple but wrong. Read all the answers here.

Ma7moud

Radar works by bouncing a signal off an object, with wi-fi nothing bounces off anything.
You are right, I meant the idea in general. For distance bounding protocols, You send a challenge through a wireless medium to the other object, if this object responds within a threshold of time, then it is in vicinity. Otherwise, it is far away. That's why ToF module is needed because such kind of measurements would never give a good accuracy without a dedicated hardware.

Ma7moud

Simple but wrong. Read all the answers here.
How come? tens of paper are published since 1993 addressing this issue, and I've already demonstrated it myself on an AVR microcontroller with IEEE.802.15.4 transceiver with ToF facility enabled in it and got a resolution up to 2ns, this means 30 cm. Since in Arduino there is an AVR MCU too, I wanna try it over there with another type of wireless communication. 

srnet

#19
Dec 13, 2017, 10:36 am Last Edit: Dec 13, 2017, 10:37 am by srnet
How come? tens of paper are published since 1993 addressing this issue, and I've already demonstrated it myself on an AVR microcontroller with IEEE.802.15.4 transceiver with ToF facility enabled in it and got a resolution up to 2ns, this means 30 cm. Since in Arduino there is an AVR MCU too, I wanna try it over there with another type of wireless communication. 
But that's something different to your original post.

Would it be possible to do this on custom hardware at either end, then yes is probably the answer. That you cannot buy modules on eBay suggests its not as easy as you might think.

However your original suggestion was between an Arduino and a Android phone.
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Grumpy_Mike

Quote
got a resolution up to 2ns, this means 30 cm. Since in Arduino there is an AVR MCU too, I wanna try it over there with another type of wireless communication. 
So you think you can measure 2nS with a processor that has a 62.5nS clock?

TonyWilk

... Look at ToF-based distance bounding protocols ...
Google, google, goolge...

Interesting... it seems another use for WiFi TOF/location is to bound access to a router based on physical location of a mobile device. So, even though the RF extends well beyond a building, the protocol could refuse access outside it's walls. Neat.

Yours,
 TonyWilk

Qdeathstar

#22
Dec 13, 2017, 01:49 pm Last Edit: Dec 13, 2017, 01:55 pm by Qdeathstar
I know it is possible to triangulate exact positions using wifi..... they use wifi as an indoor gps, i think they do it with signal strength.

it's not exactly hobby level yet. Maybe you can contact mit and ask them for their source code :)

https://www.technologyreview.com/s/542561/wi-fi-trick-gives-devices-super-accurate-indoor-location-fixes/



basically, you need several wifi access points, then you measure the rssi of their signals, reject signals that appear to be bounced, and then triangulate its position.

A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

MrMark

. . . IEEE.802.15.4 transceiver with ToF facility enabled in it . . .
I haven't played with Zigbee, but this is interesting.  What transceiver has this capability?

vinceherman

basically, you need several wifi access points, then you measure the rssi of their signals, reject signals that appear to be bounced, and then triangulate its position.
I wonder how, when measuring signal strength, you can identify signals that have been bounced?

TonyWilk

I know it is possible to triangulate exact positions using wifi..... they use wifi as an indoor gps, i think they do it with signal strength.
*snip*
You are right, although (18 months ago when we looked at it) this was pretty unreliable. Now with multi-antenna beam-forming it may be a lot better.

The newer "WiFi Location" makes use of WiFi FTM (Fine Timing Measurement) for measuring TOF to sub-nanosecond. Google it.

Yours,
 TonyWilk

jremington

Quote
I know it is possible to triangulate exact positions using wifi
Define "exact".

Qdeathstar

#27
Dec 13, 2017, 11:20 pm Last Edit: Dec 13, 2017, 11:27 pm by Qdeathstar
^within a foot.


http://news.mit.edu/2016/wireless-tech-means-safer-drones-smarter-homes-password-free-wifi-0331

Off the shelf today with any wifi adapter you can get within 6ft

Off the shelf you can get within 6ft, but you need to move a wifi antenna around.

https://securitystartshere.org/page-software-moocherhunter.htm
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Ma7moud

I haven't played with Zigbee, but this is interesting.  What transceiver has this capability?
Look at this:

http://www.metirionic.com/en/technology.html

I'm hoping to find something similar to Arduino boards with some kind of WiFi or BLE modules.

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