Hot answers tagged

47

Note how it says "330ns", a proper inductor would have a value in Henries. My guess is that this is an Analog delay line like this: Note how it has 3 connections of which one is ground which is connected to the tube and the shield. I actually came across one of these many many years ago, probably in some video equipment I scrapped for parts. At the time ...


38

First: What's critical isn't so much that there's a ground pin for each signal as much as that there's a ground pin near each color signal. The cross-shaped ground pin largely satisfies that requirement. Second: DVI doesn't prioritize high-quality analog video -- it's a Digital Video Interface, after all. The small loss of quality incurred by using a single ...


24

The analog TV signal was originally designed to be decoded with the smallest practical number of valves (tubes). Thus about half the signal space (30% of the signal amplitude and almost 30% of the time) is dedicated solely to synchronisation pulses easily detectable by analog valve circuitry, and the picture information is left with only the other half Any ...


23

I used to work at Panasonic on their In-Flight Entertainment systems, so I know a bit about this kind of stuff. This description won't be 100% technically accurate (some naming might be a bit off) but I am trying to write it so anyone can understand it. Hopefully this explanation helps... The "magic" behind it can be a combination of the following things: ...


21

This is not an answer, but I'm not allowed to submit a "comment". As for what this component does, separate processing/filtering of video luminance and chrominance introduce different (group) delays in the two signals. This can become noticeable in the TV picture (see, for example https://www.bbc.co.uk/rd/publications/rdreport_1973_35). The delay line ...


17

The HD-15 (aka DE-15) connector for VGA connection was compatible with hand-crimping of pins to conductors of coaxial elements of the multiwire connecting cable. That practically requires a two-pin set for each of R, G, B video signals, to accommodate a signal pin and ground (coaxial shield) pin. Those signals were not logic level, and lacked the noise ...


13

As others have said, PAL and NTSC are analog and have virtually no latency. This is extremely important when flying FPV drones at high speeds. Having latency will tell you where you’ve been, not where you actually are. I have a large video/photography drone (Yuneec Q500 4K). It transmits the video digitally on 5.8 GHz using the 802.11A protocol. (Just ...


11

An analog video signal is basically a waveform. It's 100% time based, and one frame takes a specific length of time to transfer, since that is how long the wave is. The wave itself takes a certain amount of bandwidth, which is basically how much data is held in that wave. It's possible to reduce the amount of bandwidth required through various filtering ...


11

You can compress analog video so it uses less bandwidth, at the cost of quality: slow scan television. Used to transmit live television from the surface of the moon, in blurry monochrome. These days we can have colour HD from the surface of Mars. It's worth looking at how the various digital compression techniques work in detail, but they all rely on ...


10

You are confusing the DVI connector with the cable. That "single" analog ground is a big honking ground, but what goes into a cable? The simplest is a DVI-A cable, which usually has a VGA connector on the other end. Internally, it will carry 3 color channels (red, green and blue) and 2 sync: vertical and horizontal. And guess what? A DVI-A cable will ...


9

Bluetooth is a half-duplex radio technology that has a peak raw data rate of 1, 2 or 3 Mbps, depending on the specific modulation scheme being used. In practice, an application can get at most about 200 KB/s of data throughput. Even if you reduce your video requirements to quarter-VGA (320 × 240) at 10 fps with 8 bits/pixel (768 KB/s), you'll still ...


8

Unfortunately in my experience what you'll quickly find is that video is obnoxiously difficult to manipulate without a lot of cpu power. Let's start from the beginning: how much video do you want? There are a lot of choices here, but start small. Let's say that, for simplicities sake, you wanted a 640x480 frame of 8-bit black and white video, at 24 frames ...


8

I understand that it's a lot to transmit, but let's focus on how to interface the arduino with the camera Arduinos are not suited for video streaming at all. Here are some of the reasons: At their best, they can only do 20 MIPS Don't have nearly enough ram They're only an 8bit processor The don't come close to having enough bandwidth to stream video ...


8

Your camera's sensor is probably saturating in daylight so attenuating the video signal would just mean that everything looks grey rather than white. The only cure is to use a lens fitted with an iris to reduce the amount of light entering the lens. Better still, fit an automatic iris lens which uses the video signal to adjust the iris aperture to keep the ...


7

I upvoted Nettle Creek's answer, but here is a quick explanation about why latency matters: Piloting a drone is a feedback system with you in the loop. As in any other feedback system, the usual Nyquist stability critera apply. Video latency adds lag in the feedback loop, and the effect is the same as on any other feedback system (you are the opamp): it ...


7

At worst the recording device will saturate (and the camera element may be damaged), but the playback device will only generate an intensity that it is capable of. There is no danger to vision that would not normally be present with the playback device.


7

The width of the HSYNC signal was 6 us, out of spec of 2.8 ... 5.3 us for AD725. The mother circuit had the location to source this signal (as video processor outputs 4.7 max, and prolongation of the pulse was introduced down the circuit), and I reused this signal. Now circuit works properly in both NTSC and PAL mode. Small dot crawling and ripple exists, ...


7

I found the answer to this some time ago, posting it here in the hope it will help others. The reason 1 byte is sent immediately on enabling DMA, is because a DMA request (DRQ) is still active from the last time that TIM8 ran. TIM8 keeps running and raising DRQ signals, even after all the bytes in the buffer have been written and DMA stops. TIM8 is gated ...


6

This 3M cable is available in 7 to 50 twisted pairs. Outer diameter for the 8 pairs is 5.84mm. Available from Digikey, not cheap. The ends shown seem to be untwisted, which often happens during stripping of the isolation. If you want to be sure the cable has enough twists (about 1 full twist every 5cm is nice), ask a sample from 3M. Make sure to check the ...


6

This patent refers to "rabbit ears" as distortions in the video sync pulse. You can see why they're called that from the shape below. http://www.patentgenius.com/image/5374960-2.html


6

You need to have the vertical sync at 60 Hz (minimum), but if you're concerned about the video dot clock speed, you can simply have fewer pixels per horizontal line. Many microcontrollers can generate VGA quite nicely if they have a hardware SPI controller, which can be configured to pump out the pixels, while the H and V sync signals are produced by the ...


6

This is going to be an extremely tedious project to get working. Here's how to do it, though: Sample the composite video signal at 5.5 MHz (the bandwidth of composite video) using a high-bandwidth ADC. Look for the line sync pulse. Once you've got that, you have a line of video in your buffer. Looking in your buffer, find the colorburst section of the ...


6

This is why VGA displays didn't happen until long after the Z80. Block graphics with sprites, or 1 bit per pixel monochrome graphics, or character ROM based display modes were the order of the day. Sometimes you could switch modes between them. Using character ROMs, the ASCII character code provided most of the address into ROM, with (scan line mod 10) ...


6

If you are interested in how digital video is sent there are a number of current standards which are relevant. As you mention VGA it is worth focusing on digital signalling designed to work between device and screen, rather than broadcast standards. Right now there are three standards for consumer devices and each has an excellent Wikipedia article: DVI, ...


6

Since you're using fairly low frequencies, this will be straightforward but tedious. What you'll need to do is to divide each channel into 3 segments - left,horizontal center and right, and bottom, vertical center and top. Then feed the 9 combinations (permutations, actually) to your 9 monitors. You make the 6 segments using op amps. Let's say, just for ...


6

Because the video is baseband. That means that it is NOT modulated onto a VHF or UHF carrier. You are asking to take the audio modulated onto a HF carrier and combine it with the baseband video signal. And then to demodulate the audio back into baseband at the other end of the cable. That has the deadly combination of costing more, plus being lower quality. ...


5

Even LCD monitors will not look as good as normal if you try to do the vertical refresh rate at 30Hz. Do be aware that LCD monitors do not have a memory that remembers all the screen display pixels from one vertical frame to the next. Instead the monitor will require a continuous flow of video data in order to see a persistent active screen image.


5

A simple solution could be a blinking LED in the video. If the perspective is static the LED could be in the scene, otherwise some (fixed) position in the frame. You trigger the LED and log this event with the datalogger. Then use something like simpleCV (OpenCV vs. Matlab vs. SimpleCV) to detect the blinking event, thus you know the significat frame numbers....


5

EDID is used, among other things, to query the monitor for the timings it would like. It isn't used to transmit any video information. I guess it's been so long that no one remembers, but VGA monitors back in the day had adjustments for the image location on the CRT. You could move it left or right, up or down, or scale it horizontally or vertically. More ...


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