Hoagie
Posts: 119
Joined: Sun Sep 23, 2012 7:19 pm

The Speed of Light

Sat Oct 22, 2016 3:54 pm

Hi,

I recently decided to try and measure the speed of light directly using a Raspberry Pi. Here's a writeup of the project, including circuit diagrams and source code.
http://www.ceirogstudios.co.uk/sol/sol.html

Hope some of you find it interesting.

Thanks,
Geoff.

mattmiller
Posts: 2243
Joined: Thu Feb 05, 2015 11:25 pm

Re: The Speed of Light

Sat Oct 22, 2016 4:40 pm

:)

User avatar
Burngate
Posts: 6306
Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK Tralfamadore
Contact: Website

Re: The Speed of Light

Sat Oct 22, 2016 5:39 pm

ok, since time goes faster at the top of a mountain than at the bottom, with that result you should be able to work out your altitude.
My estimate is that you're on top of a high mountain. Very high.

Hoagie
Posts: 119
Joined: Sun Sep 23, 2012 7:19 pm

Re: The Speed of Light

Sat Oct 22, 2016 5:51 pm

Burngate wrote:ok, since time goes faster at the top of a mountain than at the bottom, with that result you should be able to work out your altitude.
My estimate is that you're on top of a high mountain. Very high.
I'd expect most people wouldn't try this unless they were high.

User avatar
bensimmo
Posts: 4638
Joined: Sun Dec 28, 2014 3:02 pm
Location: East Yorkshire

Re: The Speed of Light

Sat Oct 22, 2016 6:01 pm

You might find this interesting
http://codeandlife.com/2012/07/03/bench ... pio-speed/
though not up to date and doesn't include pigpio
http://abyz.co.uk/rpi/pigpio/index.html
you might find piscope shows you some things too.

Also not that the R^2 value is pretty much zero, that if i remember correctly means you best fit line for teh intercept is pants.
Also you should show the error of the final value. Just to complet it.

Nice though and we do similar (though not with the pi) but with a modulator and demodulator, via a laser and use an 'scope to detect a pulse (Picoscope DSO here)
also through a fibre optic, and use similar for speed of sound in metal rods.

Though If I have time i'll have a play with your setup too :-)That'll be a while though.

Hoagie
Posts: 119
Joined: Sun Sep 23, 2012 7:19 pm

Re: The Speed of Light

Sat Oct 22, 2016 6:11 pm

bensimmo wrote:You might find this interesting
http://codeandlife.com/2012/07/03/bench ... pio-speed/
though not up to date and doesn't include pigpio
http://abyz.co.uk/rpi/pigpio/index.html
you might find piscope shows you some things too.

Also not that the R^2 value is pretty much zero, that if i remember correctly means you best fit line for teh intercept is pants.
Also you should show the error of the final value. Just to complet it.

Nice though and we do similar (though not with the pi) but with a modulator and demodulator, via a laser and use an 'scope to detect a pulse (Picoscope DSO here)
also through a fibre optic, and use similar for speed of sound in metal rods.

Though If I have time i'll have a play with your setup too :-)That'll be a while though.
Interesting link, I guessed direct access would be fastest, but went for the ease of WiringPi. Looks like I accidentally made a good choice there.

Yes, about those error bars... I kind of made a point of not mentioning those. I suspect there's a lot of luck involved in getting the result I did. Increasing the loop count to a million gives nanosecond repeatability, so the next time I get the house to myself I'll see how well those points line up.

veronicathecow
Posts: 25
Joined: Wed Oct 05, 2011 9:10 pm

Re: The Speed of Light

Thu Mar 16, 2017 8:32 pm

Hi Geoff, I saw your project whilst looking for anything about voltmeter interfacing, nicely done this is what Pis are about having fun.

I was wondering if you would consider it cheating to add a couple of bit of circuitry that might give you better accuracy?
My thought is the Pi operates a circuit that produces a very fast clean edge to trigger a very high speed counter (linked to an oscillator) and the start of the laser pulse (You may get a faster lase if you have a pre thershold current running through the laser first but this is just a guess)
A high speed photodiode could then stop the counter and this could be read through the GPIO pins at your leisure.
Have fun
Tony

Return to “Other projects”