Do any of you have the know-how to build...
 

A digital-to-analog converter? I certainly don't, but I'm wondering if any of you guys who know all those scary technical words like "Chroma demod" have thought about building you own converter box?

I mean is this the type of project that could be done ala the good ol' Radio Shack 100-in-1 electronics projects thing?

Do plans exist on the web? Certainly if you can build a nuclear bomb using smoke detectors and plans from the internet, it must be possible to build a converter!?

Discuss...:scratch2:

You could probably build one, but I believe you'd need certain microprocessors, various IC's and some surface mount stuff.

Since the convertor works with a digital signal, I highly doubt a radio shack 100 in 1 projects kit could be capable of being turned into a working convertor. I think the signal would have to be decoded, converted to analog, modulated, etc.

I was actually joking about the radio shack 100-in-1 thing. More thinking about the similar "breadboard" aspects.

Probably if you had the right components, and a schematic to follow, a breadbord convertor ***might*** be possible, though I really have no idea.

A google search turned up digital to analog convertor kits, but they aren't for television signals.

It could be done, but the cost of the parts alone would be more than a ready made converter. You'd need to have multi layer circuit boards made for the SMD and BGA components. You'd also have to write software to run on the micro controller. A degree in EE and software engineering would also come in handy.

Interesting idea, I wouldn't even know where to start with such a thing, but I wonder if it could be done with the old fashioned components we're all used to: tubes, caps, coils and such things, even if the converter had to be the size of a big tv-radio-phono combo set.

It's a little off topic, but has anyone found any particular converter good for tv dx? The one thing that dissapoints me the most about the switch to digital tv is I will not be able to dx with my old sets, since 1996 I've been living in apartments and been unable to put up an antenna, and it looks like by the time I will be able to have a place to put up an antenna, it won't be of any use to me anymore.

I should confess that the reason I'm posting is because I had an idea for an electronic product, and although I can totally visualize it, I'm certainly not at the level of electronic IQ to build it.

Do you mean a digital-TV-to-analog-NTSC converter? Those tuners are extremely complex overall, but devices like that are made from "building blocks" also known as integrated circuits and reference designs. I am sure that any number of AK members (maybe even I) could design one if we had the tools (design notes/specifications from the specialized chip manufacturers) and, especially, the time required to accomplish such a product. The cost would be absolutely prohibitive, by the way. The development/evaluation kits and license fees for the hardware and software you would need probably cost thousands of dollars, and we have not even begun to think about the value of the time to be put into the project-probably hundreds of hours, minimum.

Oh, if you meant any D/A converter, you could build a basic one with a few TTL ICs and some resistors. It would convert "digital signals" (say, 8-bit binary signals) into an analog voltage (say, zero to five volts) corresponding to the number of positive bits in the digital signal.

If you mean something in between these two extremes, ultimately the best way to do it is still to use existing D/A converter chips such as those made by Burr-Brown and customize the interface/control circuitry to accomplish your idea. Again, there are probably some AK members who could do a project like this, but don't count on it being inexpensive unless you can line up a few hundred or more customers in advance. Is this a closer answer to your question?

It could be possible to build a digital tuner but it would be pointless, since buying one would be cheaper. Now modifying a TV so it has a digital tuner, now that would be something. I’m not just talking about hiding the digital tuner inside the TV, I’m thinking more like modifying it so not only it has a DT, but also the front controls are fully functional.

Like for example, taking a Sony KV1946r (the one with the 14 channel neon displays) and modifying it so not only it has a digital tuner, its using the neon display to indicate what channel your on. Or taking a TV with a rotary tuner and modifying it so you can still use the same controls to change channels with.

Now that would be one hell of a project, don’t you think? :yes:

I don't see why you couldn't feed the IF output from a manual tuner into the IF input of a digital decoder. The channel bandwidth is the same as NTSC, but I don't know if the IF frequency is the same. It would be interesting to try it.

Since the digital signal is transmitted on regular uhf channels, would it be possible to have a digital decoder between the tuner output and the if strip of the tv?

Bill R

It would be very difficult to swap out the IF from a turret tuner into a digital stb (set-top box), without being a software engineer to rewrite the STB's firmware. A daunting task to say the least.

The ATSC digital signal has a program table that the stb firmware alias back to a specific frequency for the needed stream where it expects the "program" to be (ie CH 14.1, 14.2, etc. are "programs" on the stream). These are determined when the stb does a search of available stations (streams).

When you choose an ATSC program to watch, the stb's processor sets up the RF tuner to present the demodulation hardware the required stream, then the processor sets the demodulator to decode the correct program on the stream. There are a number of parameters passed to the demodulator, including screen resolution, audio and video program ID's etc.

Without this, there would need to be at least two actions to change the "channel" -that is, select a program. One would be to select the correct "turret" tuner's setting to present the stb the correct stream (ie select whatever RF channel the ATSC channel would be on), and then you would have to select the correct "program".

This assumes that the tuner you're attempting to interface to is stable enough for the 8VSB signal.

All the ATSC receivers I've used default to the main stream when tuned to a channel. From there you should be able to flip through the sub-channels by hitting channel up/down. A simple experiment would be to connect an ATSC receiver to the output of a cable box (or an old UHF converter). It would have to be the type of cable box that doesn't demodulate the audio and video.

In a word, no. The demodulator part can be squeezed into about a 1.5 to 4.5 inch high rack mount chassis using the latest FPGA (field programmable gate array) chips. The huge number of transistors (logic gates) are needed for the adaptive equalizer, since the digital signal must have all "ghosts" cancelled before the signal can be demodulated. At that point, you have a stream of digital bytes (MPEG Transport Packets), and you need an even more huge number of transistors to do the motion-compensated decoding of the MPEG bit reduction algorithms.
So, your closest hope would be to do a multi-layer PC board using the custom chips that have been designed for these tasks. What originally filled a series of a dozen or so 19-inch-wide by 6 foot tall racks in the early 90s now is on 3 or 2 or even 1 custom chips in a digital TV. The "Digital Terrestrial Converter Boxes" that qualify for the government $40 coupon will probably all have a single "system on a chip (SOC)" that takes the IF from the tuner and goes all the way to composite video and stereo audio for your old TV.
You could conceivably design at home a tuner system (RF, mixer and perhaps IF stages) to feed the above-mentioned digital stuff, but you still might have some difficulty if the SOC needs some particular interfacing.