Which video mod for composite?

[Dukes909]

Great! And don't forget the stripboard, too!

DesSony

Have some left over from an earlier project !

[dessony]

Great! I am eager to know the result from you!

As for the stripboard, Track, with its two end arrowheads, means copper strips. Is my artwork clear to you?

DesSony

[Dukes909]

Great! I am eager to know the result from you!

As for the stripboard, Track, with its two end arrowheads, means copper strips. Is my artwork clear to you?

DesSony

I think so although what I have is bare stripboard (not really sure what the proper term is) without any copper on it. I will just join wires (soldered) across between components. I do have a ton of this stuff that I bought for Arduino projects but find it a big hassle to connect adjoining rows (I am sure I am doing it incorrectly). Thank you for the help and your diagram!
https://www.amazon.co.uk/Prototype-Univ ... s9dHJ1ZQ==

[1024MAK]

Agreed. I also have the 210E version ULA and it outputs a fine video signal with a back porch pulse. No 555 required. All you need to get a good composite video signal is a simple transistor amplifier. The circuit mentioned at the end of the previous post should do just fine.

So the 210E version is the only one I can get away with the transistor amplifier? I will get the transistor ordered tomorrow, if I can find it anywhere . I think I have the rest of the components already. I look forward to 1024MAK's reply about the ULA differences if he can point me to them. I have a few other ZX81's and T-1000's I will convert when I know which mod for which ULA.
Cheers everyone
Dukester

Sinclair designed the ZX80 to work with black and white (monochrome) low cost television sets. These normally don’t care about whether the video signal includes the part of the signal that is called the back porch.

The ZX81, TS1000 and other localised versions are effectively an improved but lower cost version of a ZX80. Hence the original ULA chips in them also don’t have circuitry to generate the back porch part of the video signal.

However, Sinclair became aware of problems when these were used with some colour televisions. Hence the third and final ULA version had extra circuitry included in the ULA to generate the back porch. This is the 2C210E ULA.

Note that there is no such thing as a standard circuit for a television. Each designer creates their own circuitry. As a result, some colour TVs (both CRT and LCD) will actually work okay with ZX81 or TS1000 that have one of the earlier ULAs (2C158E or 2C184E). But the only way to find out is to try. Bizarrely some LCD TVs work differently with a composite video signal compared to their RF/VHF/UHF TV aerial input!

Most colour TVs however, do need to see the back porch part of the video signal, as they use the video signal level at this point to determine the ‘black’ video level. They then automatically calibrate themselves so that they can display a picture with good contrast. If the video signal is incorrect (which it will be for a 2C158E or 2C184E ULA) the TV will produce a very dark image with very poor contrast.

Note that a TS1000 can have either a 2C184E or a 2C210E ULA.

There is some further information on the difference variations in this post (this link is also in my sig.).

If your machine has a 2C210E ULA, then it does not need extra circuitry to provide a back porch. But if you want to modify it to output a composite video signal that is suitable for a TV or monitor, it is strongly recommended that a transistor buffer circuit is used. There are many variations of this. My design is in this topic (also linked in my sig.).

The transistor can be any reasonably high gain small signal NPN signal transistor (e.g. BC547C, BC548C, BC549C, 2N2222, 2N3904 etc.). But note that not all these have the same lead out (pin out). So you can’t put a 2N3904 directly in place of a BC548C in the same orientation as the connection order of the leads is different.

Mark

[1024MAK]

Great! I am eager to know the result from you!

As for the stripboard, Track, with its two end arrowheads, means copper strips. Is my artwork clear to you?

DesSony

I think so although what I have is bare stripboard (not really sure what the proper term is) without any copper on it. I will just join wires (soldered) across between components. I do have a ton of this stuff that I bought for Arduino projects but find it a big hassle to connect adjoining rows (I am sure I am doing it incorrectly). Thank you for the help and your diagram!
https://www.amazon.co.uk/Prototype-Univ ... s9dHJ1ZQ==

You have matrix board with copper pads.

Some of the other variations are:

• Plain matrix board (just holes drilled 0.1” apart but without any copper pads)
• Tri-pad. Groups of three holes with a copper PCB track linking them. Repeated over and over again.
• Strip board (stripboard). Also known as Veroboard (trade name). Each row of holes is linked by a continuous copper PCB track across the whole board.
• Various more complex designs of pads/tracks/holes, with power distribution PCB tracks - design intended for use with digital chips such as the 74 series or the 4000 series.

Note that in addition, the substrate can be SRBP / FR-2 / Paxolin (trade name) plus various other trade names. Or it can be fiberglass / FR-4. Other types are far less common.

The copper tracks / pads can either be just plain copper, or be tinned (actually HASL) and hence have a bright silver/grey colour.

Some have screen printing showing identification information.

Mark

[Dukes909]

You have matrix board with copper pads.

Some of the other variations are:

• Plain matrix board (just holes drilled 0.1” apart but without any copper pads)

Mark

Another great explanation, thanks. I have both the matrix board with and without. I have a hard time getting a line of solder across the ones with copper pads to join adjoining pads difficult. I am sure there is a vid on it that shows a better way than my putting a tinned bare wire across 2 or 3 and then adding more solder. Usually messy! .

[Dukes909]

Sinclair designed the ZX80 to work with black and white (monochrome) low cost television sets. These normally don’t care about whether the video signal includes the part of the signal that is called the back porch.

The ZX81, TS1000 and other localised versions are effectively an improved but lower cost version of a ZX80. Hence the original ULA chips in them also don’t have circuitry to generate the back porch part of the video signal.

...
If your machine has a 2C210E ULA, then it does not need extra circuitry to provide a back porch. But if you want to modify it to output a composite video signal that is suitable for a TV or monitor, it is strongly recommended that a transistor buffer circuit is used. There are many variations of this. My design is in this topic (also linked in my sig.).


Mark

Great background and explanation, thanks! Mine gives a poor picture on my LCD TV/monitor. The ancient RCA CRT I have is an even worse picture than this one. I will check the transistors I have to see if any will work. Thanks Mark!

[Moggy]

Personally I would go with Mark's design as I have found that the simple transistor mod doesn't give good quality display results when used on modern LCD type displays, being more suitable for CRT composite use.

[Dukes909]

Personally I would go with Mark's design as I have found that the simple transistor mod doesn't give good quality display results when used on modern LCD type displays, being more suitable for CRT composite use.

I do have a 2N2222 so I am good to go there but no female RCA jack..fiddlefaddle

[Dukes909]

So what is probably obvious to everyone except me.. Do I snip the 3 leads into the existing RF modulator and use the center one for the +5V source in Mark's design?