If we asked you to name Alexander Graham Bell’s greatest invention, you would doubtless say “the telephone”; it’s probably the only one of his many, many inventions most people could bring to mind. If you asked Bell himself, though, he would tell you his greatest invention was the photophone, and if the prolific [Nick Bild] doesn’t agree he’s at least intrigued enough to produce a replica of this 1880-vintage wireless telephone. Yes, 1880. As in, only four years after the telephone was patented.
It obviously did not catch on, and is not the sort of thing that comes to mind when we think “wireless telephone”. In contrast to the RF of the 20th century version, as you might guess from the name the photophone used light– sunlight, to be specific. In the original design, the transmitter was totally passive– a tube with a mirror on one end, mounted to vibrate when someone spoke into the open end of the tube. That was it, aside from the necessary optics to focus sunlight onto said mirror. [Nick Bild] skips this and uses a laser as a handily coherent light source, which was obviously not an option in 1880. As [Nick] points out, if it was, Bell certainly would have made use of it.
The receiver is only slightly more complex, in that it does have electronic components– a selenium cell in the original, and in [Nick’s] case a modern photoresistor in series with a 10,000 ohm resistor. There’s also an optical difference, with [Nick] opting for a lens to focus the laser light on his photoresistor instead of the parabolic mirror of the original. In both cases vibration of the mirror at the transmitter disrupts line-of-sight with the receiver, creating an AM signal that is easily converted back into sound with an electromagnetic speaker.
The photophone never caught on, for obvious reasons — traditional copper-wire telephones worked beyond line of sight and on cloudy days–but we’re greatful to [Nick] for dredging up the history and for letting us know about it via the tip line. See his video about this project below.
The name [Nick Bild] might look familiar to regular readers. We’ve highlighted a few of his projects on Hackaday before.
Bell labs invented the laser. Just sayin.
Ah yes, the culpeper file wasn’t it ?
Why go looking for a 10,000 ohm resistor when an ordinary 10k would also do?
But the latter wouldn’t have the right precision ;-)
+1
Whoosh?
10k has too few zeroes. Needs moar them zeroes.
Light based communication made me think of 1984 Dune, early in the film there were light based communication
wow.
In the 1930s, there had been Lichtsprechgeräte (light phones).
https://www.kriegsfunker.com/radios/LiSpr80.html
And in the 1700s the Optical Telegraph. Which – as well as the inspiring the Clacks of Discworld fame – also gave us networking concepts like control characters, flow and rate control, data routing, packet priority, tokenised channel control, error correction, etc.
Fiberoptic before it was cool
Before transistors and valves, telephone signals were amplified along long lines by a carbon capsule amplifier that used the sound to vibrate a capsule of carbon granules just like the carbon microphone at the handset, only, it was passing a much larger current, which provided the amplification.
The selenium resistor is essentially working the same point, amplifying the weak signal from light to a much stronger electrical current. Now imagine if they had used this method to amplify sound on the telephone network: you could have a grid of selenium cells connected to different outgoing lines, and you could steer the beam of light to any of those cells using a mirror. Amplification and signal routing in the same device.
I spent 10 years doing workshops for children at the Alexander Graham Bell Museum in Baddeck, Cape Breton, Nova Scotia. I also made a replica of the light telephone which I showed to the visitors. Bell invented many other things which are shown at the Museum and a visit is well worth your time!
This. The (eventually man-carrying) tetrahedral kites were particularly impressive
https://www.scientificamerican.com/article/alexander-graham-bell-goes-and-flies-a-kite-for-science/
Well not only was the first wireless telephone it was also the first wireless transmission of audio at all (that I know of) since if predates radio. Also if you wanted to use it at night a lime light would have worked, now there’s your steampunk wireless.
If we asked you to name Alexander Graham Bell’s greatest invention, you would doubtless say “the telephone”
No. Because I learn history. Bell do not invent the telephone. Meucci was.
Yup. There were Antonio Meucci and Philipp Reis, too.
But Bell had money and patents, two things that matter the most in the US.
But it’s still weird that Meucci apparently isn’t being mentioned more often in US history classes considering he was half American (Italian who moved to US).
So it’s not as if he couldn’t have been sort of a national hero, too.
But that being said, we talk about a land that thinks that Edison was a real researcher.. ;)