Hey everyone, I guess it's been a while since I've done one of these. Life and the pandemic just kind of got in the way. I've still been working on projects. I just wasn't really in the mood to film them. I kind of needed the space to just zone out while I worked on stuff because projects are my way of de-stressing and this has really been a stressful year. But I'm really excited about the project I just finished. It's been kind of a long-term project for the past month and a half, two months. So I thought I'd film something and show you guys how it works. I don't know what I'm going to call it yet. I'm sure I'll have thought of a name by the time this video publishes because the video's going to need a title. But right now I'm just calling it the optical audio decoder. What it does is it plays back the optical audio track that's recorded onto 16mm film. I'll explain how that works. There's a little bit of technology there, but first I want to give you a little bit of background about optical audio or optical sound. As most of you probably know, when the film industry started, films were silent. But by all the 1920s, inventors and studios were experimenting with ways of adding sound to film. Since film records light information, the easiest way to do that was to record sound optically. And so what they did was add a little track down one side of the film where they could record that sound, as you can see right here. Last year, a friend of mine gave me a broken old 16mm projector that had belonged to his dad. He said, you know, if you want to fix this, it's yours. And so I took it and I fixed it. And I bought a spool of 16mm film. It was a movie about isotopes. I bought that at the flea market and I noticed that it had an audio track on it. And so as I looked at that film, I thought, you know, it would be pretty cool to play that back. My projector is an old one and it didn't have any way of playing back sound. So I thought it might be kind of neat to build something I could attach to the projector to play the sound back on that film I had bought. Ultimately, I got lazy and I didn't do it. I just kind of put that thing away and that projector sits up in my rafters now because I don't have a place, as you can see, my house is kind of a cluttered mess. But this summer, since we're under quarantine and I can't go anywhere or do anything, I've been hanging out in the workshop a lot and I started to revisit the idea of building something to play back the audio track on that film. The basic idea I came up with was to put a light source on one side of the film and a light sensor on the other side of the film. And as the film passes through them, that optical track will vary the amount of light hitting the sensor. And if that sensor can convert that light level back into sound, then we shouldn't theory be able to listen to it, right? Very simple idea. It's a lot more complicated in practice. It turns out and I'll explain why. One thing that's difficult about doing that is that the resolution of that audio track is very fine. There's a lot of sound waves. If you look at the track, there's little squiggles. There's a lot of sound waves cram into a very tiny area. And so you need a very fine resolution device to read that back. And so what I needed to do was find a way to make a very narrow slit that light could shine through so it would only capture a very, very tiny sliver of the film at one time. Front of mine suggested his name is Kenneth. Kenneth Finnegan, you can find him on Twitter. He's pretty great. Kenneth suggested that I try using a razor blade. I ended up using two and I three printed a little device to hold them. The other thing I needed to figure out was a sensor that would work for this. My first thought was to try a light dependent resistor because I have a bunch of them. I have a whole bag of them. But not very much light makes it through that tiny little gap between the razor blades. There's only a very, very minuscule amount of light that gets through. And light dependent resistors just simply aren't sensitive enough to that level of light. So that didn't work. Then I tried a photodiode which worked a little bit better. I actually started to get a little bit of sound coming out of this thing when I pulled the film through it. But it was really, really, really quiet and it was very muffled. A front of mine suggested I try a thing called an OPT101 which I had never heard of before. But it's a kind of trans impedance amplifier. And don't ask me how that works. I don't really get it. I'm not an electrical engineer and I don't understand electronic theory. But in essence what it is is a photodiode that's matched with an op amp and they're matched in some way that makes them particularly more sensitive than other kinds of light sensors. So I bought a couple of those on the internet and I wired one up to an amplifier and I could actually start to make out a human voice. And that was a really exciting moment for me because it kind of felt like I was resurrecting a ghost or like doing a say-ons. Like probably no one's heard that person's voice in decades and decades. And like I'm pulling this piece of film through this thing stuck in my vice and my garage and there's a voice coming out of it. And that was really, really cool. And really not to work was the hardest part. And really the rest of this build was just like the electrical and mechanical stuff to support the playback. Really all it is is it's that read head that's doing all the magic. And then there's a box that holds all the other electronics. So there's a stepper motor that has a big wheel on it. It's a 3-printed wheel. And the stepper motor wheel pulls the film so that the film loop goes around and around. The rest of the build was just getting all that mechanical stuff to work and getting it to look the way I wanted. I don't know. I was kind of trying to go for like 19, 20s, 1930s. I don't know. Radio punk. I really don't know what you call it. Like that look of electronics in the 1920s and 1930s when there was a lot of wood and there was a lot of like make a light. I designed it to play film loops just because I thought it would be a fun variation on the audio tape loops that a lot of musicians have used for making music. I don't really know what else to say about this project other than that I had a lot of fun building it. I've not invented anything. These are this is technology that's existed since the 1930s. I just recreated it myself in my own garage. But I really had a lot of fun making it. So with that said, I guess I'll just leave you all with some footage of it playing. So thanks for watching and I'll see you next time.