Hardware and Software for Mechanical Television System This document provides all the required information for being able to build / tweak a mechanical narrow band television similar to the prototype show in this Youtube video: http://www.youtube.com/watch?v=tslWfnsTwPg . Building-up and tweaking this kind of mechanical and electronic hardware requires some experience and a lot of patience. Electromechanical parts (speed response vs torque of the available motor , disc inertia and size) have an impact on the global system behavior, so that the prototype will not be “plug-and-play”. A lot of adjustment means have been implemented in the schematics to face this kind of issues. However, it remains possible that you will have to modify some values/components to match with your mechanical configuration, especially in the motor synchronization system (as in all other kinds of mechanical TV designs). If experienced in homebrew design but not familiar at all with NBTV and/or mechanical television, first have a look to this well documented website: http://www.earlytelevision.org/dupouy.html The design proposed in this document is modular so that it is possible to chose some parts from it, if not all of them, according to one's preferences: * Video synchronization extractor + Y / green extractor * Motor driving system disc synchronization with video * Vsync triggered stroboscope for an easy adjustment of vertical synchronization by the user. * Low loss LED anode voltage regulator (avoids thermal dissipation issues and reduces power consumption), made with very common components. * SECAM-like color decoder + audio separator, if willing to build a color TV (includes a PIC1F819). No particular design is proposed for the audio amplifier since any kind of audio amplifier (having an input impedance higher than 10K in case of a color system) can match for this purpose. For the prototype shown in the video I simply used as audio amplifier a small IC demo kit that I had saved from the trash at my workplace… Input signal and main features Like many other NBTV systems, this proposed piece of hardware handles a narrow band video signal stored in a specifically generated computer file. The file type is WAV, commonly used for audio recordings: A classical lossless 2-channel (stereo) recording file at 48000 spl/s. Therefore it makes sense to talk about pixels like in digital video, because the video signal sampling rate directly gives the number of produced pixels per second when scanning a line (even if you plan to reproduce this signal later with some custom analog equipment). In case of a black-and-white system: - The first channel is used for composite monochrome video (Vsync/Hsync/Lum) - The second channel is used exclusively for audio In this case where you don’t use the color decoder, you will have at least to insert this filter between the computer audio channel output and the audio amplifier input to suppress the color carrier superimposed by default by the software converter. (If the amplifier has no volume control, insert a 10K potentiometer - as a voltage divider - between the filter output and the amplifier input) In case of a color system: - The first channel is used for composite green video (Vsync/Hsync/Green) - The second channel is used for low-pass filtered audio + SECAM-like color carrier (alternatively providing the blue and the red color signals. No YUV optimization is handled at this time). Mechanical rasterizer, resolution and size The mechanical scanning system is based on a Nipkow's disc. However the electronics could be used to drive other mechanisms (drums, mirror screws...). But we will assume for paper simplification that a Nipkow’s disc is used. Experimenters willing to build their own Nipkow’s disc can use this helping SW tool: http://users.tpg.com.au/users/gmillard/nbtv/DXFNipkow.zip The electronics and the video generation software tools are designed to be compatible with 30-line and 60- line discs, while reserving the first line for a HSYNC signal. In other words, the first line sector is present on the disc (and the corresponding hole can exist) but is it always black, bringing the effective resolutions at 29 and 59 lines. The rasterization is horizontal like in classical video (unless the original video has already been rotated before creating the NBTV video), and its speed is 12,5 frames per second. The prototype shown in the Youtube video is based on a Nipkow’s disc spinning at 12,5 turns per second. It is relatively small, especially if dealing with 60 lines (*). (*) This experience helped to conclude that such a small disc featuring so many lines can only be built with advanced machining equipment. Even a printed template and a careful driller will not succeed into reaching a satisfying result. This is why generated pictures shown in the video are disappointing. Handmade discs should be 30-line discs with a diameter close to what can be seen in the video (27 cm) or 60-line discs, two times bigger if targeting an aspect ratio close to 1:1 and a reasonable picture size. Aspect ratio considerations The goal of building such a small disc was to optimize the ratio [Picture width] / [Disc diameter] by creating shrunk pictures on the disc which could be horizontally extended with the help of an anamorphic lens. However, this prototype particularity is just an example and all the stuff presented here can be used with more classical Nipkow’s discs, provided that some care is taken for the aspect ratio: The original video file to be processed by supplied software (detailed further) must have the same aspect ratio than the final picture to be created on the disc (directly depending on disc geometry). The video converting program will adapt the entire original images to fit in a NBTV video at 57x59 pixels (or 121x29 pixels for 30-line variant), whatever are the initial and the final picture resolutions. In other words, pixels may not be "squares" depending on what you do: With 60 lines the effective pixel shape proportions are almost the same than the disc-created picture proportions, while with 30 lines the ratio height / width is the quadruple. (Pixels are in fact more similar to small bars perpendicular to lines, like in the most current cases of 30-line television systems. Ideally the disc holes should have the same proportions and shapes but this is not possible). Controls, output devices and sensors a) External controls are - One user-controlled pushbutton for vertical synchronization adjustment (The original design of the Youtube video had a far too much complex system) - One user-controller potentiometer for fine adjusting the free run disc speed - One user-controller potentiometer for adjusting the sound volume (optional) - One power switch, of course ;-) b) Output devices or actuators are: - A white power LED in case of a black and white system, for disc lighting (video driven back light): For example, a 900mA LED - Avago ASMT MxE2 or Mx22. - An RGB triple LED in case of a color system, for disc lighting (video driven back light): For example, a 3x300mA RGB LED – Broadcom/Avago ASMT-MT100-00001 - The disc driving motor: A DC motor reaching the unloaded speed of 12,5 rps (750 rpm) at a voltage between 6 and 15V. - A simple LED used as stroboscope to help synchronizing the disc (any LED rated for 30mA pulsed) c) Sensor: An IR reflection detector SFH-9201 (Infineon / OSRAM) is used as optical sensor for disc speed control. Each disc revolution generates 30 pulses. So in case of a 60-line system it counts “double lines”. The synchronization system can handle an incoming video at 30 synchronization pulses per second as well as at 60 synchronization pulses per second (1 video pulse on 2 is then used). This small SMD component is mounted on a separate circuit board and protected from a too strong disturbing ambient light by a plastic cap taken from an old photo film box. The black and white cardboard counting track features 30 B/W cycles. Adjustments The schematic diagrams include many adjustable potentiometers (to be mounted on circuit boards) which are intended for system tuning and should not require further settings as soon as everything is properly working. Unless otherwise specified, all potentiometers tagged “Px” are these kinds of potentiometers that the user will not have to use. Power supplies The primary power supply shall be a DC voltage source within 12-16V. If the disc driving motor requires more than 9V5 for reaching the target speed, the low limiting power supply value will not be 12V but the required motor voltage + 2V5. In the schematic diagrams this power supply voltage is marked: “V DC IN (+)”. The post-diode voltage “VP” is provided (in this example) from the synchronization extractor schematic. This power source is used by circuits requiring power but without accurate voltage regulation. The regulated 9V voltage used by several different circuits is provided by a 7809 regulator mounted on the synchronization extractor. (This regulator location choice is also not mandatory). It is marked “P9V”. If used, the color decoder has its own power supply architecture: Directly connected on “V DC IN”, it has its own internal voltage regulator providing 5V through the source signal “VDD”. The only dependency that this circuit has from the rest of the appliance is the video synchronization signal (positive composite synchronization Hsync/Vsync from the synchronization extractor). By processing the SECAM carrier channel it is able to drive the red and blue LEDs directly. Other signals shared between circuits Wire terminating arrows tagged with signal names are signals: - Generated by the circuit if the arrow is oriented output-wise.