Let's Measure the Speed of Light (Part 2): The DIY Edition

This is a follow up video to "Let's Measure the Speed of Light" • Let's Measure the Spee... .
That video covers some of the history of determining the speed of light and then does an experiment to measure it using a Laser Diode as source of light pulses and and Photo Diode as a light pulse detector.
This video goes over further details of how to carry out the experiment yourself using as little as $300 worth equipment and parts. Other ways of generating a suitable series of light pulses for measuring the speed of light are also covered, including pulsed LEDs, Xenon stroboscopes, Laser Distance Measurer tools, and a light chopper made with a dremmel.

[@ElectromagneticVideos]

PARTS LIST Here is the list of parts mentioned in the video: Laser Diode : Osram PLT5 522EA_Q LED Diode : Marktech Optoelectronics MTE5066NK2-UR Photo Diode : Advanced Photonix PDB-C156 Mounting Hardware : 323 Quick Release Clamp Adapter and Manfrotto 200PL-14 Plate Signal Generator : JDS6600 60MHz (or any of the identical ones!) Oscilloscope : Almost any 50Mhz Oscilloscope or better. Distance Measurer Tool : Mastercraft (Canadian Tire) 057-4691-6 If you do the experiment let me know how it went! And if you found alternate or better parts, also let me know and I will update this list.

[@syitiger9072]

Hay can u do a test with 2 6gauge stranded wire connected with an ideal red wire nuts up to 50amp please

[@ElectromagneticVideos]

@@syitiger9072 I just looked at the UL approved wires combination for the Ideal 76B which I think is the one you are referring to. It seems to be too small to be approved for two of #6 so probably not a good idea to test or use. I would be concerned that not all strands get properly secured. You probably should consider a larger wire nut or other connector type....

[@ThriftyToolShed]

Great video. Thanks for sharing the experiment details and knowledge with us.

[@ElectromagneticVideos]

Thanks so much! It was a fun thing to do!

[@MVVblog2]

I would have thought of using SPDIF optical cables, one very long and one very short. Without using lasers, simply using SPDIF hardware. But I have no idea if this type of standard hardware has the necessary speed to conduct the experiment.

[@ElectromagneticVideos]

What brilliant idea! Just did some googling. Came across this great app note : google ST AN5073 - I cant seem to get a simple link to it. Looks like symbol (pulse) rates of 15MHz rates are possible so much like my 100ns pulse. Down side is max length is 10m (30 feet) so probably a 40ns trip time (due to slower speed in a fiber). They say limitation is due to attenuation from the cheap fiber. May also be due to the thick fiber being multi-mode. That is, multiple zig-zag reflection paths inside the fiber end to end which will smear the pulse as distance increases. Must be within a few 10s of ns at 10m distance for the system to work. Digikey has two potential transmitters and receivers in stock: Toshiba TOTX1350(F) (Transmitter) CLIFF Electronics FCR684205R (Receiver) Less than $20 for the both. Swapping in a short and long cable as you suggest with a similar experimental setup as mine would be a great classroom demo. I also wonder if one could (without the fiber) use some lenses like I did to focus and concentrate the light on each each end and do an across room demo. As I recall from my own AV gear, the Toslink emitters are quite bright. I might try this in the fall sometime. Would be great if someone reading this tried it and told us how it went! Note: your comment came though twice - I will repost this as an answer both in case something weird went on with KZbin!

[@obagbemisoyejoseph212]

You are doing great, Sir.

[@ElectromagneticVideos]

Well thank you so much!

[@rokiedecentra9656]

Really useful, tried to measure the speed by shining a cheap laser diode from a sensor kit onto a photo diode from the same sensor kit over a ~6m + ~6m reflected distance. Picked up too much noise and couldn't see any time delay between the pulse of the function generator and the pulse I measured. Was quite a mess, will definitely revisit it. I didn't have a short distance and long distance... just one long distance. Was hoping the scope would pick it up but i think i am limited by the slow devices and noise...

[@ElectromagneticVideos]

Speed and noise was my problem too - found that many lasers and photodiodes don't have their speed listed and and not optimized for the speeds needed. At the top of the comments for this video is a pinned comment with parts I used. Is your photodiode a pin diode? That with a significant reverse voltage (9V or 18V) will drop the capacitance across the diode and give you the speeds needed. I was getting so much noise it was unusable until I soldered the photodiode leads right to the resistor and battery. I originally had 20cm long wires from the photodiode to the resistor and battery. Noise being picked up was unbelievable - all the switching power supplies etc sure make homes a noisy RF environment these days. Are you getting enough laser light on the diode? Without the magnifying glass concentrating the light, I did not get enough signal. You should be abler to measure light on/off voltage across the resistor with a multimeter as a low speed test to confirm you are able to detect the laser light. Hope this helps! Good luck!

[@buidelrat132]

The laser measuring device has a detector inside already, probing its guts with the scope might be easier than using a separate photodiode. Maybe let's tear down that Mastercrap unit?

[@ElectromagneticVideos]

And hopefully an amp driven by the diode. I was hoping that by showing the image of the device someone in the US or elsewhere might recognize it as being very similar or the same as a local store brand in their country and do some experimenting. On sale I got that one for $25.

[@MickHealey]

Oh, this is so tempting that I think I'm going to have to get involved. Thank you for the challenges. This is my first year after early retirement, so what better thing to keep me occupied. I have all the equipment, so it's only light emitter and detector costs for me. I have some ideas to ditch the laser.

[@ElectromagneticVideos]

Fabulous - what a neat retirement project! Did you see the comment below about using toslink parts? If you can figure out how to ditch the laser that would be great!

[@landonkryger]

I saw another youtuber AlphaPhoenix replicate Fizeau's setup with a 4 mile round trip and got an answer 99.3% accurate. Really interesting if you wanted to go full scale on this as well.

[@ElectromagneticVideos]

Just looked - very nicely done and nicely mechanical in the true Fizeau condition. Well worth looking at for anyone reading this! I'm probably not going to do it myself maybe inspiration for someone else to duplicate or use as a starting point. Thanks for pointing that out. The link to his video is here in case anyone wants to watch: kzbin.info/www/bejne/j36yaqiLqM-Ll6s

[@florinpetrache7834]

I think that if you use a laser focused in a focal point, passing the focal point through a rotating disc with a larger diameter and with very small and close holes, you can get much smaller pulses. You probably need a converging lens to make the beam parallel after the point focal.

[@ElectromagneticVideos]

I looked at that - couldn't find an easy combination of things that did this as well as pulsed laser. If you find a good way of ding this, I would be interested in hearing how you do it.

[@byronwatkins2565]

A LED makes a fast photodiode, but only at low reverse voltage (~6V). Its lens makes it directional and filters the light, but it also means that you have to be careful about focusing the light externally -- a focus angle larger than the LED's divergence angle will completely miss the diode. You can also use the oscilloscope's 1 MOhm input impedance to develop voltage from the diode's current, but the 'scope's input capacitance will increase the response time. Given the Dremel tool, you could mount a small mirror with the rotation axis in the mirror's plane. This will sweep the laser in an arc. An aperture or another mirror several feet away to sample this for a fraction of a degree of angle would provide a very nice pulse of light less than 5 us wide. More distance between the Dremel and sampling aperture shortens the pulse.

[@ElectromagneticVideos]

I have never tried a LED as a photodiode - I would be interesting to see how effective they are compared to a PIN diode optimized for detection. Have you tried it? How good was it compared to a purpose built one? Great idea about using the distance to an aperture to make the pulse short. I would be a bit afraid to of the mirror flying off at high speed if it came loose. Its funny you mentioned the spinning mirror. I was thinking about thinks like that yesterday and it dawned on me that the spinning scanner mirror from a junked laser printer could a great mechanism for that sort of thing. And its balanced and includes the motor. If anyone plans to try it, be aware that some laser printers (if not most these days) use a linear array of LEDs rather than a laser + mechanical scanner to draw on the photoconductor drum.

[@byronwatkins2565]

@@ElectromagneticVideos It is fast, but not very sensitive.

[@ElectromagneticVideos]

@@byronwatkins2565 Interesting!

[@gabest4]

Please excuse my silly question. Could a very good mobile phone camera replace a scope? 3840x2160 at 120fps has roughly 1ghz pixel frequency, or 1ns resolution. I have no idea how it really works, if it captures a whole line at once, the rolling shutter effect gave me the idea.

[@ElectromagneticVideos]

A very insightful thought! A lot of modern electronics does have the speed and capability of doing what we need - just not easily accessible as probably is the case in the phone camera. I think a lot of them handle line data in parallel these days to reduce the digitization speeds. Are you also thinking of the individual pixel sensors being Ghz fast? Unfortunately they are typically setup to store up charge during the period not being actually read to increase sensitivity or for shorter (but still long for our purposes) times for higher shutter speeds. Anyone have more insight as to how modern cell phone cameras work?

[@DaveEtchells]

The problem is the phone camera has a much longer total, exposure time over which it accumulates light/charge, so it won’t be able to discriminate times much shorter than 1/120s. The pixel frequency is just the clock speed of the readout from the shift register at the edge of the array.

[@h7qvi]

15ns response time corresponds to time constant of 15pF in parallel with 1k resistor. Use a 50ohm MMIC amplifier and 50ohm microstrip connections to short leads on the detector and you might get sub 1ns response time. Run a 50ohm cable to a 50ohm CRO input.

[@dl5244]

wow, I just watched a @zachstar video on the smith chart and how+why impedance matching helps for this reason

[@ElectromagneticVideos]

You know, there are a lot of easily available 50 Ohm LNAs that go from close to DC to 2GHz or 5Ghz or more. I wonder if they would would - they should have the BW for the speed.

[@ElectromagneticVideos]

Certainly - one needs to eliminate reflections with a 50 Ohm amp setup. Some scopes like my digital one do have built-in 50 Ohm resistors ...

[@dougmodlin2032]

Just watched your excellent videos! Thank you! I’m looking for a speed of light measurement that could be set-up next to a museum exhibit about Albert Michelson. We want to inspire students and their teachers so I loved your idea of designing the experiment to keep it simple and easy to visualize. I also liked your idea of using a laser measuring device as the laser source. It would seem that the device might be used to calibrate the DIY set-up since you can get the time by dividing the distance it measures by C. In the month since you posted your video have you learned anything more about what laser measuring devices work well and have you made any other improvements? Thanks again!

[@ElectromagneticVideos]

Thanks! What a wonderful thing you are doing! I havnt had a chance to do any more with it - just getting back to videos right now (half way though a halloween video -Jacob's ladders and and that sort of thing). I think the main issue with distance measurers is that they shut down after a few minutes. You might need to open one to attach wires to an external switch that can be used to periodically turn it on. Haven't experimented with any others. So far people who have been doing the experiment essentially have duplicated what I did. What about a mirrored laser scanner variant of the experiment? I guess you challenge is space - you could send the light down a long fiber. I will be trying that with the 500m of fiber I purchased this summer Email me if you get a chance - its hidden in the Electromagnetic Videos About page - maybe we can toss some ideas back and form - I'd be thrilled to help if I can!

[@dougmodlin2032]

@@ElectromagneticVideos thanks so much for your response and offer to collaborate. I will email you (assuming I can find it) 😀

[@ElectromagneticVideos]

@@dougmodlin2032 You found it!

[@steubens7]

this got me wondering about the photodiodes i've got from aliexpress, and which ones i could get from there. the bpw34 is really common & is like a little solar cell, it's slow though, 100ns. the bpw24r is in a TO-18 case with a lens and it's 7ns for about 4$

[@ElectromagneticVideos]

They both look like excellent possible candidates for the task: bpw34 : Just looked at the ams OSRAM BPW 34. The Mouser website (Mouse # 720-BPW34) has a datasheet thats seems to show 0.02 μs rise and fall with a 50 Ohm load. The capacitance is high probably due to the large area, but if you use two or three 9V batteries to run it at 18 or 27 volts you can get it down to 10pF or so and you can probably use a 1K resistor like I did for a more an output V easily readable on a scope. The bpw24r has a smaller active area and much lower capacitance. With the lens to focus the incoming light, properly aligned it can have can have a potentially much larger capture area. I would try them both!

[@fabimre]

Have you (or anybody here) thought about a beam-splitter recombination/phase detection merhid like the Michaelson Morley experiment? Of course then one has to first device a method to determine the wavelength of the laserlight precisely. Maybe as a secundairy experiment to enhance the accuracy?

[@ElectromagneticVideos]

Something like that would certainly be the way to do it if one was going for accuracy. A couple of commenters to the first "measure the seed of light" video I did mentioned it - one had done that in an undergrad physics lab in university. I wonder if there is some way to do it using minimal expensive equipment?

[@florinpetrache7834]

At magnetic amplifier ,with how many volts do you feed the circuit?I have 220v at the socket. Do you think it can be fed with a max 300v 3kw autotransformer?My toroidal transformers are 230v on the primary and 30v on the secondary, what voltage should I apply to the primary and how many turns should I add to each transformer? In your case, the 2 primaries are connected in parallel, I think. I saw a circuit on google with the primaries connected in series .How they must be tied to the end?your light bulb is incandescent (120v or 230v)or led and what light source i can use?

[@ElectromagneticVideos]

See the answer in the comments for that video here kzbin.info/www/bejne/gmWwfWNjhM5_q5Isi=oaSZ1J0xHJ8ZPM8-

[@williefleete]

That signal generator should have a “cmos” setting, which will be a square wave without going negative

[@ElectromagneticVideos]

Just checked - your right - in the same settings section as pulse. Funny - I never noticed it! Thanks!

[@florinpetrache7834]

the BNC 75ohm connectors are not probes, they only have BNC father on both ends for the signal generator at the ends. So the oscilloscope does not burn if I connect the generator directly with a voltage lower than 42v (for lisajous between 5 and 9v)?i can use BNC cables with clips at one end through probe or could I cut a BNC cable in two and connect the x1 probe to the exposed wires?

[@ElectromagneticVideos]

So you are connecting a signal generator or similar to the scope with a cable with BNC connectors on each end (or BNC on one end and clips on the other). Those types of voltages should be OK with most scopes as long as the input of the scope is high impedance which is true for most old er scopes. Newer scopes sometimes offer the option of the scope input being in either high impedance or 75 or 50 Ohms. If you have the scope set to those low input impedance, keep the voltage in to 3 or 4 volts. Note that normally scopes are used with the inputs set to high impedance.

[@florinpetrache7834]

I found an infrared laser diode of 115W, 895-915nm, 13.2v, and I don't know if I should buy it to create with light pulses, plasma in the air (that is, to ionize the air) in the focal point. Do you think it's worth buying , so do you think it can work?

[@ElectromagneticVideos]

Dont! Thats way to dangerous.

[@florinpetrache7834]

for osciloscope is good PM3082 4 cannels 100Mhz?

[@ElectromagneticVideos]

That should work well for it!

[@florinpetrache7834]

Is a 250mw red 650nm 5v laser diode or a 5mw 4.5v laser diode quite fast because I couldn't find a direct green diode. I guess the 5mw one is too weak, so is the 250mw one good?

[@ElectromagneticVideos]

The one I used was 20mW. 5mw could work if you too more care with focusing the optics than I did - also many photodiodes do better with red light than green so that would help. Speed is a different story - you need the specs of the diode. The one I used was rated for use at a 100MHz modulation frequency: 1/100MHz = 10ns so its switch on / switch off time is about half that or 5ns. There is really no way of knowing what a devices switching time is without the specs or testing it. The PLT5 522EA_Q laser I used is available from Digikey, Mouser and Newark for about US$15 so it might be easier to order one from them than go though the frustration of trying other ones. You do need a laser not much slower than that speed for the types of distance I was doing the experiment with.

[@timramich]

What causes laser light to have that glittery look? I never understood that. Is it because they're outputting a narrower band of light as opposed to other sources that are more broadband?

[@ElectromagneticVideos]

Upcoming video in that! Its because the light is coherent meaning that all the waves are synchronized with each other. Think of the waves from a single drop of water in a pond. The glitter you see is the constructive (bright areas) and destructive (dark areas) interference patterns. Look carefully at the glitters and move left or right - they generally dont move in the same way other things do at the distance they appear to be at. White light - or incoherent colored light is like the waves from millions of tiny drop falling in a pond. The waves form each individual drop forms the same sort of interference patters, but the patterns will peak in different places for the waves from each drop. All it all together and you dont see the interference patterns - they all smear together.

[@florinpetrache7834]

For Photodiode is good BPX65 with 12ns, dark current 1nA ,surface photodiode 1mmx1mm or should i buy SFH 206K or try both?

[@ElectromagneticVideos]

The SFH 206K has a much larger active surface area (7 mm²) so I would suggest you use it. The other other one with only 1mm² would require much (well 7x) the light intensity to achieve the same voltage output.

[@florinpetrache7834]

I bought a 35mhz philips oscilloscope almost like yours that has a problem that I don't know how to solve. I don't know if it has a technical problem or I don't know how to set it up. The spots don't appear from the end of the screen but appear inwards 1.5cm from at the edge of the screen up to the line, on the left side and on the right side. to the left the spot seems more intense (contracted), and to the right weaker and elongated. in the center it seems fine. Do you somehow know what it could have, or is it defective.

[@ElectromagneticVideos]

Is this what you are seeing: the oscilloscope trace does not reach the full extent from left to right on the screen, and seems to move faster right. So that is something wrong with the horizontal deflection system - the oscillator or the amplifier. A sawtooth waveform is used to move the beam left to right, and is often generated by charging a capacitor though a resistor, then emptying the charge and repeating. To keep the waveform looking like a sawtooth, the capacitor is only charged to 10% (approx) of the max applied voltage to the resistor before dumping. It could be that voltage to the resistor is low so you arnt getting full deflection and the top of the sawtooth is getting close to the lower max voltage as becoming rounded. Or something in the amp section also limiting the max voltage to the crt. So in the end, you need to either return it to where you purchased it and get your money back or have someone with electronics experience see if they can fix it. It probably is not worth paying for someones time to fix it unless the cost of that is really low where you are. So I probably would return it. or see if the sell will fix it. Thats really too bad - I know you ave been working on this a long time.

[@florinpetrache7834]

As a probe, the passive 150mhz probe is good; 10:1;10Mohm;12pf;1.2m or probe 0/450MHz;10:1:1ns;10Mohm;12/22pf, which is better? I have a lot of other possibilities and I don't know how it would be better to choose.

[@ElectromagneticVideos]

I would try one with a lower capacitance like the 12pf one, since the capacitance will slow rise or fall times from the diode. All of those speeds are fine - almost anything rated for 100Mhz or more should work. Good luck!

[@florinpetrache7834]

I found a green laser diode 510-530nm 10mw 6-7v, and I think it has PWM control mode 2000khz in condition to add 10uf capacitance duty cycle 50%. it is good this laser diode or could I try a 5mw red one?

[@ElectromagneticVideos]

What really matters is how how sharply it can be switched on or off. With pulse width control you might be able to make a suitably sharp pulse. Since it is more powerful, be really cautious that the light beam gets nowhere near anyones eye!

[@florinpetrache7834]

On the side of the BNC connector it says 1Mohm, 25pf. This means that I can use probes larger than 25pf, or can I also use probes of 12pf or smaller to do the experiment with the speed of light? Another question would be about the BNC connectors, 2 in number with a resistance of 75ohm for Lisajous pattern with a signal generator. My oscilloscope has the limit Vp=42v probe on x1 and x10 Vp=400v. BNC connectors (75ohm) are good if the signal generator is set to between 5v or 9v. I'm asking not to burn the oscilloscope

[@ElectromagneticVideos]

The values on the side of the BNC connector is what that connector/cable/probe is. So that probe has a capacitance of 25pf. Less capacitance is better (faster response time) so 12pf probes would work. The BNC Oscilloscope inputs: You usually can switch between 75 Ohms or infinite input impedance. 75 Ohms should only be used for direct connection to devices with an output impedance of 75 Ohms (ie video out of a VCR or signal generator) with a low voltage output (2 or 3 volts max). Any higher may burn out the 75 Ohm resistor in the scope. For use with probes like the 1Mohm, 25pf ones mentioned above, the oscilloscope should be set to infinite input impedance. The maximum voltage that can be used here depends on the specs of the scope and the probe. If you dont have the specs for both, I would not use more than 50V max for the x1 setting on the probe, and 10 times that for x10 setting. Hope that helps.

[@florinpetrache7834]

it is good an Osciloscope Philips dual beam PM 3214 0-25MHZ for this experiment?

[@ElectromagneticVideos]

Yes - the analog scope I used was the PM3215 which is the 50 Mhz version. Your 25Mhz should be fine. Sounds like you are close to doing the experiment - if you do, email some photos and the your results!

[@florinpetrache7834]

what is the name of your photodiode? how fast it is?is good SFH 206K (has 20ns).

[@ElectromagneticVideos]

I used the Advanced Photonix PDB-C156. I put a parts list at the top of the comments for this video in case you need other part numbers. Just looked at SFH 206K - it looks very similar to the PDB-C156 so it should work.

[@fisheye42]

At 25:00 instead of "spitting image" (exact likeness), it sounds like you said "splitting image." Was that an optics pun? 🙂

[@ElectromagneticVideos]

You got me on that one - I had look at the video at that point. I did apparently say "splitting image." I wish I was smart enough to have made a pun like that but I not. Just a blooper on my part!

[@konstantinjirecek970]

Most of the green lasers are in fact infrared laser diodes with some vawelenghth shortening crystals in front of them. Therefore tere is strong parasitic IR radiation from such lasers, sometimes more IR than visible light. Moreover Green light is delayed comparing to IR - therefore signal from green lasers is not good for such experiments. You can calculate all parasitic capacitances from the slope of incoming signal on oscilloscope that has time connstant approximately equal to R (1killohm) times Capacitance.

[@ElectromagneticVideos]

The laser I used is one of Osram's Direct Green Laser Diodes so it does not have that issue. Your comment is good caution for anyone considering using some other green laser type that might have dangerous IR emissions.

[@florinpetrache7834]

Do you still have the 50Mhz analog philips oscilloscope? I ask this because the person who wanted to sell it to me no longer wants to sell the 25Mhz one. I ask because only if and only if you want to sell it to me (you say the price). I already have 120 dollars, and for my birthday, maybe I'll make more. I still have to pay for the transport (probably postage) to Romania, where I live. Tell me if you agree.

[@ElectromagneticVideos]

Thats too bad. Sorry but I dont want to sell mine. Also shipping from Canada would be so expensive it wouldn't make it worthwhile anyway. Try looking on ebay or better yet, local online classifieds. Scopes like that often show up because everyone wants fancy new digital ones. One thing about the philips scopes - the selector push buttons do fail after a lot of use and are apparently hard or expensive to replace, so be sure to check them on any scope you are buying.

[@florinpetrache7834]

one of 20khz would be good? it has the option of min 0.020us=20ns,it is Russian, made in 1992.

[@ElectromagneticVideos]

20MHz you mean? Probbaly - I wouldn't go for a bandwidth lower than that though.

[@JohnJTraston]

A diode? You need to you tubes, buddy. And photo multipliers.

[@MVVblog]

I would have thought of using SPDIF optical cables, one very long and one very short. Without using lasers, simply using SPDIF hardware. But I have no idea if this type of standard hardware has the necessary speed to conduct the experiment.

[@ElectromagneticVideos]

What brilliant idea! Just did some googling. Came across this great app note : google ST AN5073 - I cant seem to get a simple link to it. Looks like symbol (pulse) rates of 15MHz rates are possible so much like my 100ns pulse. Down side is max length is 10m (30 feet) so probably a 40ns trip time (due to slower speed in a fiber). They say limitation is due to attenuation from the cheap fiber. May also be due to the thick fiber being multi-mode. That is, multiple zig-zag reflection paths inside the fiber end to end which will smear the pulse as distance increases. Must be within a few 10s of ns at 10m distance for the system to work. Digikey has two potential transmitters and receivers in stock: Toshiba TOTX1350(F) (Transmitter) CLIFF Electronics FCR684205R (Receiver) Less than $20 for the both. Swapping in a short and long cable as you suggest with a similar experimental setup as mine would be a great classroom demo. I also wonder if one could (without the fiber) use some lenses like I did to focus and concentrate the light on each each end and do an across room demo. As I recall from my own AV gear, the Toslink emitters are quite bright. I might try this in the fall sometime. Would be great if someone reading this tried it and told us how it went! Note: your comment came though twice - I will repost this as an answer both in case something weird went on with KZbin!

[@MVVblog]

@@ElectromagneticVideos Great! My thought was not so silly, I would like to repeat your experiment to my audience in Italy, I have many young people who follow my channel, I am sure they will appreciate it very much. Thank you for this valuable information. PS. The comment is double because I have 2 KZbin channels, I was uploading a video on the second channel but I commented as the first channel, something went wrong, you can delete one of the two comments.

[@ElectromagneticVideos]

@@MVVblog It certainly wasn't silly! Let me know if do repeated it and send me the link! Even if its in Italian, I'm sure I can figure out whats going on from the video. Are you going to try the SPDIF/TOSLINK version? No worries about the double comment!