A Slide Viewer Makes An Excellent Case For An OLED Project

Sometimes when browsing the websites of our global hackspace community you notice a project that’s attractive not necessarily because of what it does or its technology but because of its presentation. So it is with the subject of this article, [Kris] needed a house temperature monitor and found a 1960s slide viewer made an excellent choice for its housing.

The monitor itself is a fairly straightforward Arduino build using a couple of DS18B20 1-wire temperature sensors and a real-time-clock module and displaying their readings on a small OLED screen. Its code can be found on this mailing list thread if you are interested. The display presented a problem as it needed to be reasonably large, yet fairly dim so it could be read at night without being bright enough to interrupt sleep.

A variety of projection techniques were tried, involving lenses from a projection clock, a magnifying glass, and a Google Cardboard clone. Sadly none of these lenses had the required focal length. Eventually the slide viewer was chosen because it was pointed out that the OLED screen was about the same size as a photographic slide.

Slide viewers are part of the familiar ephemera of the analog era that most people over 60 may still have taking up drawer space somewhere but may well be completely alien to anyone under about 30. They were a magnification system packaged up into a console usually styled to look something like a small portable TV of the day, and different models had built-in battery lights, or collected ambient light with a mirror. The screen was usually a large rectangular lens about 100mm(4″) diagonal.

[Kris]’s Vistarama slide viewer came via eBay. It’s not the smallest of viewers, other models folded their light paths with mirrors, however the extra space meant that the Arduino fit easily. The OLED was placed where the slide would go, and its display appeared at just the right magnification and brightness. Job done, and looking rather stylish!

We’ve not featured a slide viewer before here at Hackaday, though we did recently feature a similar hack on an Ikea toy projector. We have however featured more than one digital conversion on a classic slide projector using LCD screens in place of the slide.

Via Robots and Dinosaurs makerspace, Sydney.

17 thoughts on “A Slide Viewer Makes An Excellent Case For An OLED Project

    1. Damn. Beat me to it.
      I had a 5″ green CRT and a fresnel lens setup years ago, in actual use (on an old Vic-20…). Just the fresnels left now. I should lash up a new rig with a LCD like this. And maybe watch the movie on it. That would be doubly disturbing.

  1. cool!!

    I’ve been looking for a slide viewer for a thing kinda like Luke Skywalkers “binocular” device seen on Tatooine in Ep 4, A new Hope.

    I want to use a raspberry pi, GPS, IMU, pi camera, then overlay compass heading, inclination/declination data on screen.

    besides the viewer, my biggest hurdle so far is getting the video overlay working at a “real time” rate, all the gstreamer solutions have a shipload of lag.

    the best solution I’ve come up with so far is Mr Nootropics video experimenter shield for the Arduino.

    1. Could do it old-school: analog vidicon and a CRT. Zero lag, except for the update rate. Great fun, and easy to inject arbitrary graphics on top of the video signal.

      A modern CMOS camera might be a close approximation though, if you do no buffering (i.e., update the output device on a line-by-line basis as the data streams off the camera). The damned USB stack with modern cameras is a PITA though. Unless you want to get down and dirty with the driver or roll your own, you’re generally stuck with just the completed buffered frames, at least one frame period late, and often two (at least it looks that way with the DSI/Thorlabs cameras I use). And then the output framebuffer adds its own delay too, unless you drive your own display directly.

      1. I bought one of these

        great improvement over the “standard” pi camera, the lens that came with it isn’t real flash, but I picked up a 4mm, 6mm and 8mm lens from Jaycar, they are the last stock, for AUS$18.
        Getting a bit more light, through a glass lens really helps!

        One of the local auto shop chains had a 3.5″ LCD with CMOS camera for AUS$50, so I grabbed one to try. (you can never have enough cameras or displays!)

        I’ve had the Arduino video experimenter shield for ages now

        The raspberry pi composite signal goes into the VE shield, then into the LCD.
        I have an MPU9250 IMU on the pi, connected over i2c, as is the SeeedStudio Arduino Mega, so I’ll be send heading, inclination/declination, altitude data to the Arduino to overlay on the composite signal.

        The Raspberry Pi’s UART has an XBee connected to use for terminal session control.

        After reading the recent HaD article on open thread, it might get used for network access
        As I’ve said before I have a shitload of 60mW XBee Pro’s lying around, so I might as well use them.

        The other thing a friend of mine and I have been messing around with is WiFiBroadcast

        So we went and bought a few TP-Link TL-WN722N USB WiFi dongles.

        I’ll probably have to connect the EM-406 GPS with an FTDI USB cable, doing anything on an Arduino that is generating composite video is tricky timing wise.

        it’s all progressing “fairly” well, I’m breaking the whole thing into separate “modules”, getting each to work, then I’ll integrate the whole lot into a laser cut/3D printed case.

        And yes, it is going to be a biggish thing to lug around!! (but so was that thing that Luke had!!)

        One thing I really want to add is some kind of stereo sound input, not sure which way to go with that.

        I really should start blogging all this, just in case someone else wants to share in my “insanity”!!

        1. If you can live with the resolution, that Video Experimenter sounds perfect for this application.

          I have a large monocular that optically combines an internal compass and reticle with the viewed image. It works well, and the image is much higher quality than any cheap LCD or camera. Unless you really want the electronic image (like infrared or amplified?), that might be a simpler way to go.

          1. basically I want it to update rapidly, like in the movies!
            and I want recording capability

            the other functions, because it’s going to have GPS and an IMU

            – a Predict mode, where I’ll have up/down/left/right arrows on screen to “guide” you to the ISS
            – where is , I’ve tried this with 900Mhz XBee radios, EM-406 GPS units and Arduinos, to play “Where’s the dog?”

            I figure I’ll cram as much stuff as I can physically fit in my case, most of the slide viewers (if I can find one) are fairly big and you could fit a fair bit of stuff in them.

            (It’s a pity those lepton FLIR modules are so expensive…)

          2. Yes, partially reflecting mirror like Pepper’s ghost. (isn’t Prospero’s ghost the Krell? :-) )
            (note you can get glass that’s anti-reflection coated on one side only for this application: the uncoated side reflects about 5% of the light, the coated side much less, so you don’t get that annoying double image. A proper beamsplitter is heavier and costs more.)

            But even the little bubble LED displays are a bit too big for that application. You need a magnifying glass in front of them to make the image appear at the same distance as everything else in the monocular image (i.e., infinity), which (duh) magnifies them. For a small package (that you can easily heft) the focal length is short and so the magnification is high, making the apparent size of the LEDs huge. You can make more complex optics to minify the image, or you can just get a tiny OLED or similar display (like the Kopin CyberDisplay, $5 at Electronic Goldmine, but good luck getting it working). Or a Microview. Or a NKK SmartSwitch display.

      1. my friend and i went out and bought this camera

        the “genuine” pi camera is crap, mainly because of the crap plastic lens, that has a 3mm objective.

        the CS lens supplied is a little better, but I bought a 4mm, 6mm and 8mm for $18.
        A larger objective makes a huge difference!

        I’ve been using WiFiBroadcast and it works really well, the OSD stuff is for a specific board though.

        I have an Adafruit colour LCD, that works over SPI, so you need to use the framebuffer copy.

        A local autoshop chain had rear view 3.5″ LCD monitor/CMOS camera combos for $50, so I bought one. (you can never have too many displays and cameras!)

        raspistill and raspivid use the broadcom chip to do preview, so the HDMI/composite output is pretty straight forward.

        the overlay stuff I’ve been trying has LOTS of lag, but using an Arduino with the video experimenter shield works really well.

        I really wish the Pi had more than one UART though! I’ll probably end up using an FTDI cable to get GPS data into the Pi.

        Anyone have a good stereo input solution for the pi?

        If I’m doing all this work I might as well give it the ability to record sound with video

  2. Another ‘me too’. I’ve actually got the same Vistarama viewer in pieces on my workbench, with a 2.8″ TFT going directly behind the lens to give it a sort of CRT appearance on my desk.

  3. I’m currently seeing a lot of slide projectors in the local goodwill/thrift stores (the slide generation must be dying off). And i always wonder what I could do with a couple of those lenses and some RGB leds. A digital kaleidoscope?

    1. you’ll need to put the LEDs where the slide goes.
      I tried putting a wax paper screen in a 2 1/4 square double glass slide, then had my v1 two axis laser galvo thingy in where the lamp and condenser lens assembly went.
      it was ok, but not great, v2 was way better, but not linear

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