A Plea For A Solution To The Paddle Issue

orion70 · Post by **orion70** » Wed Mar 24, 2010 8:40 am

ral-clan wrote:There is a software fix, as has been used in Orion70's PONG port of a few years ago.

Erratum: PONG by Nippur72 and Nbla000

.

Vic20-Ian · Post by **Vic20-Ian** » Fri Mar 26, 2010 4:44 pm

ok, I have opened up the Vic and have been fiddling with the capacitors.

I snipped one of them and jitter increases in clowns, snipping both causes a restricted amount of travel so I think I am on to the jitter source.

A simple capacitor in series won't do the trick as caps in series lower capacitance, it will need to go in parallel or replace the current ones.

Unfortunately they seem to be like mini diodes and soldered in so one end of the glass is flush to the pcb so removal seems best.

The schematic says they are 0.01uF. I will try a range around that.

I will source a few capacitors to replace to current ones and report back next weekend if not sooner.

rhurst · Post by **rhurst** » Fri Mar 26, 2010 4:47 pm

Incredulous report!

Pedro Lambrini · Post by **Pedro Lambrini** » Fri Mar 26, 2010 4:59 pm

Just in case the caps are the problem: How easy is it to remove and replace these caps? Bear in mind I'm far from intrepid with these things! :p

Marstedt · Post by **Marstedt** » Fri Mar 26, 2010 5:11 pm

Is there a link to that schematic?

Vic20-Ian · Post by **Vic20-Ian** » Fri Mar 26, 2010 5:20 pm

later cost reduced model I am working on c20 and c21 next to joy port.

http://www.mainbyte.com/vic20/n_schematic.pdf

original model c13 and c14 - note sure where located but from potx to gnd and pot y to gnd

http://www.mainbyte.com/vic20/e_schematic.pdf

Should be easy to replace but is a motherboard out job. I just need to hunt for some capacitors, not easy ona small island with no Maplin.

Pedro - get thee to Maplin and get some 0.001uF, 0.0022uF 0.0047uF and 0.01 uF ceramic capacitors, 4 of each and we will give it a go Wednesday night.

amramsey · Post by **amramsey** » Fri Mar 26, 2010 7:10 pm

Other things to also experiment with -

* add cap filters to pin 7 of the port. Basically filter the power going out to the joystick so it isn't as noisy when it comes back thru the pot.

* Increase decoupling on pin 40 of UB7. If the 6560 has a noisy supply, the internal A/D will have noise no matter how clean you make the POTX and POTY inputs.

* Instead of removing the caps that were on POTX and POTY and replacing with different values, you might want to consider having a couple in parallel (ie- 0.001 and 0.01). That will filter noise at different frequencies.

Not sure how fast the POTX and POTY ports are sampled, but if you increase the capacitance too much it may be a problem.

Anyhow, I'm still on the road so no way to experiment on my machine to see what helps. Good luck!

Leeeeee · Post by **Leeeeee** » Fri Mar 26, 2010 10:25 pm

The capacitors on the POTX and POTY lines are part of the RC timing circuit, the paddles being the R part, that is used to determint the paddle position. Altering the value of these capacitors will alter the measurement range of the paddles.

I'm guessing that a good start for fixing the jitter would be to filter the +5V paddle supply with a series 100 ohm resistor and a parallel 470uF electrolytic capacitor.

This could be done on a short male/female adapter that goes between the VIC and the paddles saving modifying either.

Lee.

Vic20-Ian · Post by **Vic20-Ian** » Sat Mar 27, 2010 3:07 am

Great help thanks. I hadn't considered the power supply.

I especially like the external adapter idea as I just purchased a set of 50 female and 50 male 9 pin D connectors for <£12 for a maplin speech card rework using 8 bit baby and SP0256, it uses the adaptor for access to potx.

If the external power cleanup works I will aim to develop a low cost fix for about 20-30 Vics to go between port and paddles.

Vic20-Ian · Post by **Vic20-Ian** » Sat Mar 27, 2010 6:13 am

I now don't think it is the caps c20 and c21.

I replace c20 with 0.1uF and range changed but not jitter.

Seems like RC filter on the plug may be next thing to try.

Just thought I would let you know before anyone goes out buying capacitors etc.

nbla000 · Post by **nbla000** » Sat Mar 27, 2010 7:26 am

orion70 wrote:
ral-clan wrote:There is a software fix, as has been used in Orion70's PONG port of a few years ago.
Erratum: PONG by Nippur72 and Nbla000 .

I waited a bit before to reply, thanks for your clarification Orion

ral-clan · Post by **ral-clan** » Sat Mar 27, 2010 7:56 am

Vic20-Ian wrote:ok, I have opened up the Vic and have been fiddling with the capacitors.

Thanks for doing this. I appreciate your experimentation.

sjgray · Post by **sjgray** » Sat Mar 27, 2010 10:09 am

Just a shot in the dark, but has anyone considered that it might be the VIC chip itself that is the problem?...

Steve

Leeeeee · Post by **Leeeeee** » Sat Mar 27, 2010 10:37 am

I've considered it but there's not much that can easily be done if it is.

You could add extra filtering to the VIC chip supply and, if that doesn't help, add series resistors to the address lines and P01 to reduce the driving current. This could also help with reducing noise on the video output.

The problem with this is it means either modification to the VIC board or mounting the VIC chip on a small daughterboard with all the problems that entails.

Lee.

Vic20-Ian · Post by **Vic20-Ian** » Sat Mar 27, 2010 10:56 am

I hacked in a 0.1uF capacitor inside the paddles between the wiper and ground.

Jitter reduced but freaks out the scaling of the pot a bit. I didn't drop a resistor in series and it was not 470uF in parallel with supply.

I think you mean pin 7 - 100k - cap +ve - 470uF -- cap- ve - gnd

and tap the cap +ve point to go to the potentiometer supply side. Is this correct Lee?

Looks like a possible solution with Lee's suggestion of an adaptor. When I get the bits in the post next week I will try.