VIDEOS

Examples of video output from circuits I’ve built.

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EARLY VGA TESTS

Experimenting with video synthesis using composite video is challenging because the sync signal (which keeps the image stable on the screen) is encoded along with the image signal. If you try to process the image by e.g. passing it through filter circuits or feeding oscillators into it, the sync will get garbled and your video will look like scrambled Pay-Per-View cable TV. Working in VGA is a nice way to get around this. VGA has vertical and horizontal sync (Vsync and Hsync) on separate wires from the image signal, so you can tamper with the image without messing up the sync. The red, green and blue components of the image signal each are carried on their own wire, which allows fun colour mixing.

In this example, a composite-to-VGA converter box is providing the sync signals. The wires carrying sync are connected to an LCD monitor. Instead of the wires carrying the red, green and blue image signals from the converter, various electronic signals are being connected to the RGB pins on the monitor’s VGA input.

Here, the vertical lines are generated by a TS555 chip (a CMOS version of the 555 timer chip, similar to the standard varieties but with a higher maximum frequency). The Hsync wire from the VGA converter is connected to pin 2 (Trigger) of the TS555 through a signal diode. Whenever a new line is going to be drawn, the Hsync line spits out a pulse. This retriggers the TS555 so that its oscillation is always in phase with the display – in other words, its period of oscillation starts at the same point on every line. By contrast, if the 555 is not triggered, it will create spinning diagonal lines as it goes in and out of phase with the display.

The horizontal lines are being generated by an audio synth (a Korg Monotron) with its output plugged directly into the green channel of the monitor. Don’t forget to connect the grounds of all these devices together.

The VGA converter box I used can be ordered through Monoprice. Cheaper versions are also available on eBay and probably work just as well.

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SINGIN’ IN THE ACID RAIN

In these examples, a VHS copy of Singin’ in the Rain is played into the composite input of the composite to VGA converter box. The RGB outputs of the converter are passed through some homebrew circuitry before being fed into the monitor.

The vertical lines that conform to the geometry of the original video are generated by a TS555. Here, one of the colour channels of the original video is connected to pin 2 (Trigger) of the TS555. Every time there’s an abrupt change in the voltage of the original video signal (e.g. a transition from a dark region to a light region; an edge), the TS555’s oscillation period is restarted. The result is semi-vertical lines that “echo” the forms of the original video, repeating off toward the right-hand side of the screen.

In addition to being appealing in its own right, the video-triggered TS555’s output can be fed into logic chips like the 4017 counter/divider, the outputs of which can be sent to the RGB inputs of a monitor. Intricate strobing geometric effects can be achieved in this way (to be demonstrated in an upcoming video).

The colour-changing effects are being achieved by feeding the various signals (original video and TS555 output) into potentiometers, and then into 2N3904 transistors set up in the emitter follower configuration. The transistors act as buffers, allowing the processed signals to be sent for further processing or display without overloading the preceding circuitry. The transistors are hooked up to the RGB inputs of the monitor, so the potentiometers form a simple buffered mixer. Twiddling the pots results in changing colours.


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10 thoughts on “VIDEOS

  1. Hey,

    It’s very nice to see more and more vga experiments and diy video synthesis popping up across the internet. Your stuff looks great!
    I’m working on a very similar setup as yours. I even came up with the same idea of using 555 oscillators, but I used the normal NE555, which doesn’t seem to work nearly as well as the cmos version, so thanks for that tip.
    As far as I can see, the TS555 is the same as the 7555, which seems to be even cheaper. The only gripe I have with 555’s is that there seems to be no easy way to control both frequency and duty cycle. Do you have any ideas on this?
    I’m gonna upload some documentation on my stuff very soon, for now, here’s two video doodles I recorded from my ‘videophone’:

    http://www.schaefersimon.de/blosxom.cgi/projekte/videophone.warst

    It basically consists of one of those composite to vga converters you’re using, with a vga to composite converter right after it. So far, I’ve mainly concentrated on circuit bending these devices (they’re VERY bendable), and processing internal and external feedbacks through them. I haven’t really messed with the vga signal too much, yet. But I’m slowly getting started on that as well. Since I’m trying to build a self-contained unit, a major concern of mine is to use the least components possible. So I guess I’m gonna try your 2N3904 mixing variant instead of getting lots of bulky and expensive opamps…. How well do the transistors behave in terms of buffering? Do they distort the picture in any kind of way?

    Woooop,
    Simon (der Warst)

    • Hey Simon! Thanks for commenting. I’m familiar with your project from your threads over Muff Wiggler. It looks really awesome!

      I haven’t tested out the 7555s, but if you pick some up I’d be very curious to know how they perform, so keep me posted. As far as controlling frequency and duty cycle independently, I haven’t figured that out, but as noted elsewhere, I’m not an EE and typically just get ideas from other people’s designs. Are you familiar with Thomas Henry? He’s a prolific designer in audio synth DIY – notes on many of his designs are available at http://www.birthofasynth.com/, and PCBs for some of them can be found at Magic Smoke Electronics and over on the Electro-Music forum. The reason I bring him up here is that he designed a 555-based audio VCO that’s really versatile. Over on Muff Wiggler, Fonik has photos of a really nice build of it, and at Electro-Music he is (or was) offering the PCBs and front panels for sale at a very reasonable price.

      Here’s a video of the 555 VCO in action. It sounds amazing, particularly that hard-synced saw! So I wonder how it looks? This is something I’ve been wondering for a while – is it possible to convert modules designed for audio into video modules by swapping lower-bandwidth components (mostly the op amps, I guess) for faster ones? Anyway, the point is that there’s a lot possible with a “simple” 555!

      As far as your question about mixing and buffering with 2N3904s goes: firstly, regarding functionality, it’s been a while since I tested them out, and I don’t have a very good scope, but I remember that I was having some problems getting the 2N3904s to work reliably. I’ll set them up again soon and try to do a bit of a test, and will make a post out of that with some documentation. I’ll be getting a new digital scope soon which should help with this.

      Secondly, regarding “bulky” opamps, it’s actually sort of the opposite problem – they’re tiny! Most, if not all, video/high-bandwidth op amps being manufactured these days are only available in surface mount packages. I recently corresponded with Michael Egger from Anyma, the Swiss group developing the incredible Synkie open source modular vidsynth, and we talked about chips a bit. He said that their workhorse op amp for the past couple years has been the MAX4392, and recently they’ve been testing out the LMH6643MA. Both of these are available at Mouser for $2 each, cheaper if you buy in quantity. It’s pricy compared to 2N3904s, which I recently learned you can buy at Tayda Electronics for $0.02 each (!!), but still not that bad. I just received an order of both the MAX and LMH op amps – haven’t tested them out yet, but will report results ASAP.

      As I mention, these chips only come in SMT packages, but both the MAX4392 and LMH6643MA are available in SO-8 packages, which are the largest SMT IC size. Still a bit scary for someone like me who learned to build with through hole components, but there are tons of resources online for learning SMT soldering (check out this one from SparkFun), and there are also always SMT-to-DIP adapters (pricy, though!).

      • Hey, the MAX4392 looks interesting. I just found out that farnell sells then for 72p if you order more than 10, which seems pretty reasonable. I’m based in the UK, though, so I don’t know if that’s an option for you. Lars from LZX also recommended the AD8034, because I was looking for something you can use with single supply. I got a few samples, but I’m a bit hesistant about those because they’re around £3-4 each and I’m operating on a very tight budget…
        I’m actually starting to get used to SMT a bit. Well, as long as we’re talking SOIC, because that can still be handled with stripboard and dremeling… But I also got two samples of the AD8034 in SOT23-8 packages. This is where it gets a bit silly.

  2. Hi, this blog’s great, very useful info.
    I’ve just started experimenting with VGA (using VGA to BNC cables for H& Vsync) and I’d like to try your TS555 oscillator for vertical bars, do you know where I can find a schematic for something similar?
    I’ve seen Thomas Henry’s design but I’d need something simpler to start with.
    Thanks a lot.

    • Hey Martino! Thanks for your comment. I’ve been very slack about updating lately, but have been teaching myself Eagle and designing some modules. I’ll post the schematic for the 555 oscillator design within the next few days. It’s very simple, especially compared to Thomas Henry’s – in short, it’s your run of the mill astable 555 design. Hook up your input signal (one of the sync signals, an RGB colour channel, audio whatever) to pin 5 (CV input) and take the output from pin 3.

  3. Hey many thanks for your help, I’ve tried and it worked, exactly what I needed.
    Great to hear you’ll be soon posting your modules, I’ll surely try to build them.

  4. Hi!! This blog is very inspirational. Thanks!!!
    I have a question about the emitter follower transistor configuration in your post.
    I´ve looked for info about npn transistor in common collector (emitter follower )configuration that act as a buffer, but it´s not clear for me. (Sorry, brain limited aka little retarded)
    I connect original video signal to the base. I took the output from the emmiter.
    Where do I connect the collector? And grounds?

    Thank in advance.

  5. Hi Michael,
    I’m following an electronics class and i am very interested in analog video synthesizer.
    In class we are used to use a regular 555 as a timer with a 9v battery. Are you working the same way ….sorry im very new at this!
    Thank you for your time your experimentation looks really cool

    Matt

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