Paddle problems with Vic20..

Mikam73 · Post by **Mikam73** » Thu Aug 03, 2006 6:40 am

Wonder why object on screen shakes when I try paddle game with Vic20..

But when tryed same paddles at C64 Arkanoid did work just fine..

There was earlyer talk that paddles might go bad when they get old, but now it looks like that its more Vic20 problem..

I should try my other paddles too..

Jaicen · Post by **Jaicen** » Thu Aug 03, 2006 11:36 am

If the paddles work like the C64 ones then they're discharging a cap through the paddle to ground. It could be possible that the cap is damaged, but it's more likely that the pot needs a bit of a clean. Try that first as it's pretty easy to do. Bear in mind that some games may have a subroutine to 'de-bounce' the pot values to give a more stable operation.

Schema · Post by **Schema** » Thu Aug 03, 2006 12:27 pm

I ran into this too and wrote it up a while ago.

The problem was with the VIC itself. i.e the paddle on screen shook, even if I replaced the real paddle with a normal resistor! I used a resistor with the value of the paddle "halfway". So it is definitely not the paddles.

No idea what would be wrong in the VIC.

I have several more VICs now - maybe I should try them too for comparison.

Alan · Post by **Alan** » Thu Aug 03, 2006 12:54 pm

I've noticed this issue too. I would enjoy paddle games like Super Smash and Clowns much more if it weren't for the aggravating jitter. The same jittery paddles work fine on my Atari 2600 and even my C64.

There must be some component degrading in the VIC? Or is this a problem that has always affected VICs, even 20 years ago?

Schema · Post by **Schema** » Thu Aug 03, 2006 1:16 pm

This thread has a lot of deju vu

Might as well revisit it though.

I think something has degraded. I remember paddle games working just fine as a kid. I'm using the exact same VIC20.

There's a version of Clowns fixed to use a joystick somewhere.

Mikam73 · Post by **Mikam73** » Thu Aug 03, 2006 4:12 pm

Its intresting that paddles work ok with C64, but not with Vic20..

And I am sure it didnt shake like that old times.. Who would buy/play games, if it would shake like that.. Wonder how it do with Omega Race..

Arkanoid was fun with paddles.. I wish I could enjoy Clowns too.

Jaicen · Post by **Jaicen** » Thu Aug 03, 2006 4:44 pm

As it happens, I just got an old Grandstand 5000 pong type thing with the most jittery paddles you've ever seen! It has a great light gun/rifle thing tho. Still, it was pretty much free with the Plus/4 & Datasette I got for £5!!
No PSU but I built an adapter to use an regular C64 one. Works just great.

ral-clan · Post by **ral-clan** » Thu Aug 03, 2006 6:44 pm

I have found that Atari paddles that work just fine with an Atari 2600 are jittery with my VIC-20. I cannot say I have tried to clean them with contact spray inside the potentiometer yet. I will have to try that....however, the fact they work fine on the Atari but not the VIC points to some other problem, as experienced by the users posting above.

eslapion · Post by **eslapion** » Fri Aug 04, 2006 8:19 am

As pointed out, the problem is the VIC itself.

Basically, the resistor you put on the paddle port is used to charge a capacitor that is inside the VIC every 512 cycles or about 2000 times every second.

A configuration like that is very sensitive to any electrical noise. But there is a way to fool the 6560 into thinking the capacitor is charged at a specific time and therefore have clean paddles on the VIC.

Schema · Post by **Schema** » Fri Aug 04, 2006 8:58 am

eslapion wrote:But there is a way to fool the 6560 into thinking the capacitor is charged at a specific time and therefore have clean paddles on the VIC.

Are you going to give us a hint?

Jaicen · Post by **Jaicen** » Fri Aug 04, 2006 9:05 am

How about a simple series resistor?
Something very low in series would prevent small peaks from charging the cap perhaps.

eslapion · Post by **eslapion** » Fri Aug 04, 2006 6:08 pm

Schema wrote:Are you going to give us a hint?

Take a good look at how the 1351 mouse works, there is your hint.

Jaicen · Post by **Jaicen** » Fri Aug 04, 2006 7:07 pm

What's going on with this forum? It keeps crapping out when I post or push backspace! Anyway, for the second time:

From what I can tell, the 1351 reads the position of the X and Y axis relative to it's last position, and feeds that to the SID POT registers
The clever part is the use of a binary 'noise bit' which defines wether the mouse has moved or not by comparing a stored image of the previous sample. If the noise bit is off, the mouse hasn't moved and no change is transmitted, hence no jitter.
Now, how do we achieve that using a simple 470K pot?!

ral-clan · Post by **ral-clan** » Thu Dec 21, 2006 3:56 pm

So, can anyone come up with a simple mod we can all do to our VICs to make paddle games play well again?

From what I can tell, the 1351 reads the position of the X and Y axis relative to it's last position, and feeds that to the SID POT registers

And can a 1351 mouse be made to work on a VIC-20, or can it only be used with a SID equiped computer? I assume that it can be used on the VIC because the VIC I chip has a couple A/D convertors.....(as far as I know).

eslapion · Post by **eslapion** » Fri Dec 22, 2006 4:31 am

The interesting part is not that the 1351 mouse feeds information to the POT registers but how it does it from an electrical point of view.

If at a very specific point in time you want to fool the VIC or any other machine into believing that a slowly charging capacitor has reached its "threshold point" then all you have to do is connect that capacitor to a digital chip via a smaller value resistor.

In other words rather than have a potentiometer (the paddle) charge that capacitor at a certain rate and let the VIC decide when it feels it looks like it is charged enough, replace the resistor with a digital system that will make the capacitor LOOK like it is charged or discharged at a very specific point in time that YOU decide.

Essentially, that is what the 1351 mouse does and NO, this mouse does not work on the VIC because the timing for the paddles charge/discharge is not the same as the 64. Also, on the 64, up to 4 paddles are supported because POT X-Y on the SID is externally multiplexed by a 4066.