ZX8-CC8 and 2C158E ULA (PokeMon to the courtesy phone!)

[Moggy]

@Balford


Also for anyone else who has the oldest of the ULA's (2c158e)

Connected it to Karl's video jobby and tried it on a B/W CRT TV with AV input (yes they do exist) result perfect.
Then tried it on colour CRT TV AV input, perfect. Finally tried it on LG LCD set. White level perfect, black figures sharp and clear, but noticed some rainbow effect around the letters which I'm putting down to the fact I used the same tuning of Karl's video device for all three and perhaps whilst the CRT sets would accept anything without argument perhaps some fine tuning needed for LCD? Either way will be posting ULA to You in the morning Balford as I think you will make more use of it than me if only for scope readings to add the knowledge as it were.

Regards.

Moggy.

[balford]

I've seen some occasional rainbow ghosting effects off of my ZX80Core when its CCB is slightly out of adjustment, so I'd imagine some tweaking will be required

Again thank you very much Moggy, I'm in your debt I'll 'scope the output from this new ULA for all to see when I get my grubby mitts on it

B

[balford]

For those interested, here are a couple of photos of the patient in question:

As I received it:


I gave the case a quick clean, repainted the logo, replaced the membrane and missing feet:


Lastly, an internal shot for those who like PCB pr0n


B

[dinosaur]

Well - it depends on the quality of TV/monitor you use to display.

A 46" Sony LCD TV for me. And yes, you mileage may vary depending on your TV.

I was not happy with the transistor solutions and regardless of the speed of transistor and filter you do - this is not noise from the power supply this is voltage drop inside the ULA power lanes which is measurable and viewable at output pin 16.

Agreed about the ULA signal noise, and this is exactly what I wrote by the way...
Note that the transistor speed doesn't change a thing about the noise, but if you use a "generic" (BC547 & Co) transistor, its Ton/Toff, and most important, Ts are simply too large (up to 500ns for Ts with a BC547 against 20ns for a ZTX313 or 2N2369A), which will cause trailing effects on white to black transitions and may also degrade the sync.

Keep in mind that in the video signal 700mV is the difference between white and black and already 5-10% noise (35-70mV) can be seen on a white background.

The noise is not seen *at all* for me on the white: like I explained, the signal is in fact a little (*) too strong (over 1V peak-to-peak) and the white level saturates the video input of the TV, so whether there's 70mV more noise added doesn't change a thing (it's just clipped by the TV circuitry together with the excessive white level).

You can reduce this with individual contrast/brightness settings but when you connect it to a 42 inch plasma TV as I do, you can surely see those thin line pattern in the background and it is true that it is depending on the CPU usage during video display and you can see when the data is delivered for a character, when it is latched and so on. These actions do slightly voltage drops on the ULA output which is not as steady as it should be for a good analog signal.

Like I explained (and shown in the photo I posted), this is only seen on the black wide areas, as dark grey vertical lines, but they are barely visible even when using an excessively high brightness setting. For the best results, you'll want to push the contrast setting to the max and the brightness to the minimum (given the saturation, even with a minimum (0 !) brightness the ZX81 white screen stays very bright for me).

And of course I am not happy to change the default/custom settings of brightness and contrast on my home TV for just the ZX81 display.

My TV remembers a different setting for each input, and the AV1 input I'm using the ZX81 onto was unused, so not a problem for me.

(*) EDIT: quite stronger, actually: 2.2 Vp-p, measured on a scope, with black/backporch level at 1.1V and white level at 2.2V... For a result closer to the norm, I could probably replace D9 with two diodes in series(**), so to lower the signal by 700mV...

(**) EDIT 2: I tested the two diodes in series trick: with two 1N4148s, I get 1.6 Vp-p and I indeed can see the noise/vertical strips in the white background, but I also get a much deeper black. With one 1N4148 and one BAT85 (Schottky diode) in serial, I get 1.8V peak-peak, the white is saturated and noiseless again, and the black is still very deep (much better than with just one silicium diode); I adopted this latter solution, which definitely gives excellent results with my TV set (but your mileage may vary, depending on the AGC characteristics on the composite video input of your TV...).

[PokeMon]

Note that the transistor speed doesn't change a thing about the noise, but if you use a "generic" (BC547 & Co) transistor, its Ton/Toff, and most important, Ts are simply too large (up to 500ns for Ts with a BC547 against 20ns for a ZTX313 or 2N2369A), which will cause trailing effects on white to black transitions and may also degrade the sync.

I use logic gates (74LVC1G86 and 74LVC1G08) in ZX8-CCB with a typical delay of 3ns. Why use a transistor when you can get a complete circuit for nearly the same price/size.

And there is another feature, you can adjust the pixel size ratio between black and white and get them more equal when using another trigger point on the edges. So you can adjust the letter size a bit between stronger and lighter.

[dinosaur]

Note that the transistor speed doesn't change a thing about the noise, but if you use a "generic" (BC547 & Co) transistor, its Ton/Toff, and most important, Ts are simply too large (up to 500ns for Ts with a BC547 against 20ns for a ZTX313 or 2N2369A), which will cause trailing effects on white to black transitions and may also degrade the sync.

I use logic gates (74LVC1G86 and 74LVC1G08) in ZX8-CCB with a typical delay of 3ns.

Nice

Why use a transistor when you can get a complete circuit for nearly the same price/size.

The price of a 2N2369A is between 1 and 1.50 euros... I doubt you sell your circuit for such low a price... Beside, for a French ZX81, it costs nothing at all: the ZTX313 is already there and the only thing you have to do is to *remove* components to get a quite nice composite sync output instead of a shitty UHF output.

And there is another feature, you can adjust the pixel size ratio between black and white and get them more equal when using another trigger point on the edges. So you can adjust the letter size a bit between stronger and lighter.

Again, very nice. Don't take me wrong: your circuit is probably top notch, but I personally prefer the self-made solutions, and for a ZX81 with a good ULA (backporch present, strong/healthy signal on pin 16), there's little point in bothering with a more expensive solution when you can get a very decent (quite sufficient as far as I am concerned) result in 10 minutes.

[PokeMon]

Why use a transistor when you can get a complete circuit for nearly the same price/size.

The price of a 2N2369A is between 1 and 1.50 euros... I doubt you sell your circuit for such low a price...

So - when you take the logic gate you have about less than 50 Cent per IC. The whole price is about 7 EUR (GBP 5.80) but this is complete with 3 gates (logic IC's), pcb board, some passive components, trimmers and complete soldered, tested, adjusted with wires soldered to the board for easy use. So on the other hand not really expensive. But is okay to do the transistor mod, no problem. There is by the way another feature, you can easily invert the video signal with a jumper or even use a switch. Try that with your single transistor.

[dinosaur]

There is by the way another feature, you can easily invert the video signal with a jumper or even use a switch. Try that with your single transistor.

Don't dare me !

[1024MAK]

Is this a game of ping pong?

Mark

[Moggy]

Is this a game of ping pong?

Mark

I hope not such games tend to end badly.

I think it should be noted that whilst those who posses such skills are happy to go their own way Karl's little board is ideal for those of us who are users rather than doers, that why I bought three of the buggers!!

Plus at just over a fiver they are a bargain considering you are also paying for Karl's time in assembling them.