PROPHET64 & MSSIAH Userforum




Official information and support forum for
MSSIAH and all PROPHET64 versions.



You are not logged in.

#26 2006-08-08 16:11:07

firestARTer
Administrator
From: Germany
Registered: 2006-06-27
Posts: 579
Website

Re: Making Pots More Accurate

Thats the Job the capacitor is doing.


firestARTer - Gameboy - C64 - Atari Music
Hardware developing for your favourite homecomputer musicsoftwares
http://www.sidsyn.com
http://www.myspace.com/firestartermusic

Offline

 

#27 2006-08-08 16:13:46

AxiMaxi
PROPHET64 GURU
From: The Netherlands
Registered: 2006-07-09
Posts: 548
Website

Re: Making Pots More Accurate

firestARTer wrote:

Thats the Job the capacitor is doing.

You mean your additional cap?


If everything is under control, you're not going fast enough.

Offline

 

#28 2006-08-08 16:27:46

firestARTer
Administrator
From: Germany
Registered: 2006-06-27
Posts: 579
Website

Re: Making Pots More Accurate

Yep, it actualy decreases the need of the full resistor value. You can calculate this by some simple electronics calculations:

T = R*C
T = 470K * 1000pF (the capacity is taken from the original datasheet)
T = 0,47m

Then you use the formula to get the new capacity depending on your resistor: (lets take 200k for example)
C = T / R
C = 0,47m / 200k
C = 2,35 nF   ( but they are not possible to get, so 100K and 4,7nF are just fine, or you would have to use 2 x 4,7nF and put them in a row )

Thats for your education!!


firestARTer - Gameboy - C64 - Atari Music
Hardware developing for your favourite homecomputer musicsoftwares
http://www.sidsyn.com
http://www.myspace.com/firestartermusic

Offline

 

#29 2006-08-08 16:33:39

AxiMaxi
PROPHET64 GURU
From: The Netherlands
Registered: 2006-07-09
Posts: 548
Website

Re: Making Pots More Accurate

firestARTer wrote:

Thats for your education!!

Hey thanks!
I knew I'd get there in the end wink tongue

Now, please continue working on the MIDI interface big_smile


If everything is under control, you're not going fast enough.

Offline

 

#30 2006-08-08 16:35:41

firestARTer
Administrator
From: Germany
Registered: 2006-06-27
Posts: 579
Website

Re: Making Pots More Accurate

hehe....acutally i am waiting for the midi-software, until then i am doing some other cool things that you guy will like and organizing all the stuff for my forthcoming russia tour smile


firestARTer - Gameboy - C64 - Atari Music
Hardware developing for your favourite homecomputer musicsoftwares
http://www.sidsyn.com
http://www.myspace.com/firestartermusic

Offline

 

#31 2006-08-08 16:41:21

Jaicen
Centipede
Registered: 2006-07-14
Posts: 461

Re: Making Pots More Accurate

I'm assuming that T = time taken to charge the cap?
So what you're doing is adding a capacitor in parallel with those on the board, increasing the time constant (ie, it takes longer to charge to full voltage). Therefore it needs a larger voltage change to give the same values, pretty efficient. I'm assuming that the cap is wired from the wiper to ground?
What i'd be interested to know, since I can't actually find the datasheets, are if the capacitors used for this RC network are the same on the C64C board as they are on the original. Which caps are they? Got a link to the datasheet?

Offline

 

#32 2006-08-08 16:45:26

firestARTer
Administrator
From: Germany
Registered: 2006-06-27
Posts: 579
Website

Re: Making Pots More Accurate

Jaicen wrote:

I'm assuming that T = time taken to charge the cap?
So what you're doing is adding a capacitor in parallel with those on the board, increasing the time constant (ie, it takes longer to charge to full voltage). Therefore it needs a larger voltage change to give the same values, pretty efficient. I'm assuming that the cap is wired from the wiper to ground?
What i'd be interested to know, since I can't actually find the datasheets, are if the capacitors used for this RC network are the same on the C64C board as they are on the original. Which caps are they? Got a link to the datasheet?

No, actually the capacitor is nearly loaded at 5 T.
The SID datasheet is here:
http://stud1.tuwien.ac.at/~e9426444/sidtech.html

There are different capacitors in the C64's revisions. But working with the datasheets is just fine.


firestARTer - Gameboy - C64 - Atari Music
Hardware developing for your favourite homecomputer musicsoftwares
http://www.sidsyn.com
http://www.myspace.com/firestartermusic

Offline

 

#33 2006-08-08 16:52:27

basil faulty
Dan Dare
Registered: 2006-07-19
Posts: 73

Re: Making Pots More Accurate

a quick schematic would be cool!

Offline

 

#34 2006-08-08 17:00:07

firestARTer
Administrator
From: Germany
Registered: 2006-06-27
Posts: 579
Website

Re: Making Pots More Accurate

The 20th post here in this topic are the schematics


firestARTer - Gameboy - C64 - Atari Music
Hardware developing for your favourite homecomputer musicsoftwares
http://www.sidsyn.com
http://www.myspace.com/firestartermusic

Offline

 

#35 2006-08-08 17:09:44

basil faulty
Dan Dare
Registered: 2006-07-19
Posts: 73

Re: Making Pots More Accurate

Doh! Sorry

Offline

 

#36 2006-08-08 17:10:50

firestARTer
Administrator
From: Germany
Registered: 2006-06-27
Posts: 579
Website

Re: Making Pots More Accurate

smile no prob


firestARTer - Gameboy - C64 - Atari Music
Hardware developing for your favourite homecomputer musicsoftwares
http://www.sidsyn.com
http://www.myspace.com/firestartermusic

Offline

 

#37 2006-08-08 17:19:07

basil faulty
Dan Dare
Registered: 2006-07-19
Posts: 73

Re: Making Pots More Accurate

So, for my 470K pots I will need 1N caps?

Hey, I can use a calculator!!!

Offline

 

#38 2006-08-08 21:11:00

Jaicen
Centipede
Registered: 2006-07-14
Posts: 461

Re: Making Pots More Accurate

Ok you've lost me there, the cap is loaded at 5T?? So it takes five times the time co-efficient to charge the cap? That doesn't make a whole lot of sense.
Link's broken too..

Offline

 

#39 2006-08-09 23:38:19

basil faulty
Dan Dare
Registered: 2006-07-19
Posts: 73

Re: Making Pots More Accurate

OK...

I have new POTS (470K Linear, different brand)
I have 1N Caps
All wired up as per schematic above
I am using a different motherboard (252311 Rev.4)

STILL only half travel! In fact, the caps made it worse so I removed them.....

Offline

 

#40 2006-08-10 00:45:08

Jaicen
Centipede
Registered: 2006-07-14
Posts: 461

Re: Making Pots More Accurate

Ok, the link works again now it seems. Pretty straightforward, the caps are just tied to +v via the pots, so as far as I can see there's no need for an earth, the cap is already tied to earth on the PCB. The paddles don't need to be voltage dividers, they're simply acting as a current limiter.
According to the datasheets, the larger the cap is, the less jitter there is on the values. It would therefore be logical to assume that to keep the same time constant range with a larger cap, you would need less resistance.
In this case, it would require that if you double the capacitance to 0.2uF (2000pF), a pot of around 220K will give you roughly the same range with much less jitter (actually, 200K would be better, but they're hard to find as pots). The cap will need to be connected across pin 8  (ground) and pin 9 (the wiper of the pot). No need to mess with the PCB, just solder them on to the back of the D connector.

Last edited by Jaicen (2006-08-10 00:56:51)

Offline

 

#41 2006-08-10 02:09:18

Jaicen
Centipede
Registered: 2006-07-14
Posts: 461

Re: Making Pots More Accurate

I just did some experiments, and it seems that .1uF is about the size limit for the caps before the time constant becomes too large. I tried a .1uF in parallel with the onboard cap (across pins 8&9), but it gives 0 to max and nothing in between. I tried it with smaller value pots, down to 190K (470K + 680K parallel resistor), but to no avail. I found that using just a 200K pot gives a good range of values using virtually the whole rotation, but the jitter remains. Anybody got any ideas?

EDIT: I just re-read the first page of this discussion and can now see Firestarter's diagram which pretty much makes my earlier post redundant. Sorry about that!

Last edited by Jaicen (2006-08-10 12:11:12)

Offline

 

#42 2006-08-10 09:16:47

AxiMaxi
PROPHET64 GURU
From: The Netherlands
Registered: 2006-07-09
Posts: 548
Website

Re: Making Pots More Accurate

Just an idea, without theoretical background: why not remove the cap in the C64?


If everything is under control, you're not going fast enough.

Offline

 

#43 2006-08-10 13:22:15

Jaicen
Centipede
Registered: 2006-07-14
Posts: 461

Re: Making Pots More Accurate

Because that is harder than soldering a cap to an external port, that can be removed later, thus making it a reversible mod. Many people don't want to be de-soldering their motherboards!
For what it's worth, i've now settled on what i'd say is the best pot configuration possible without mods to the motherboard. That is a 100K pot, with a 472 (0.0047uF) cap across pins 8&9. I only use one pots so I haven't tried multiples, but since this is pretty much the same setup Firestarter is using, i'd assume that it would work fine. I get 95% usable rotation and a lot less jitter than without the cap.

Offline

 

#44 2007-08-24 18:19:29

klx300r
Nibbler
Registered: 2007-05-31
Posts: 42

Re: Making Pots More Accurate

Jaicen wrote:

Because that is harder than soldering a cap to an external port, that can be removed later, thus making it a reversible mod. Many people don't want to be de-soldering their motherboards!
For what it's worth, i've now settled on what i'd say is the best pot configuration possible without mods to the motherboard. That is a 100K pot, with a 472 (0.0047uF) cap across pins 8&9. I only use one pots so I haven't tried multiples, but since this is pretty much the same setup Firestarter is using, i'd assume that it would work fine. I get 95% usable rotation and a lot less jitter than without the cap.

Jaicen, could you please provide a picture of your mod and/or a simple sketch...Ive followed this thread and it sounds like your method is the way to go!

Offline

 

#45 2007-08-25 02:29:33

gossi
Rockford
From: Iceland
Registered: 2007-08-17
Posts: 50

Re: Making Pots More Accurate

When connecting the pots as described in the manual I get practically jitter free operation although the values max out at 50% rotation.
I find that if I skip the connection to pin8, the pots have a wider working range but they interfere with each other. That's unacceptable, so I reconnected pin8.

For me, maxing at 50% is not really a problem. With 5 bit values it's relatively easy to get the values you want in such a short span. Guess I'll have to live with it.

(unless of course somebody here has a real magic solution smile
btw, my 470k pots measure 440k

edit: I found out that connecting pin8 actually doesn't make any difference.  The reason the pots interfered with each other once I cut the connection to pin8 was that both pots were still connected together (using the same wire that went into pin8)

as soon as I cut the connection between the pots I revert back to 50% range but lose the interference.

Last edited by gossi (2007-08-25 04:06:14)

Offline

 

#46 2007-10-22 10:19:31

ktronik
Bloody beginner
Registered: 2007-10-22
Posts: 1

Re: Making Pots More Accurate

Just plugged in my 'cart' this weekend, & got a system up & running... so me Newby... but may have a idea you can try...

I grabbed 4 C64 paddles (500k pot), swapped the wires left to right ( to make turn the same way)


I put a 1meg trimpot 'across' the 2 wired pins on the 500k pot, I put the 500k pot to MAX on the 'port test' & just dialed in the 1M trimpot till the port meter backed off a tiny bit..I then gave back a wisker...I repeted for the other 3 paddles & now have all the 500k pots, 100% travel. ( on the bassline & monosynth ) I will try the caps as well to smooth them out...


while I was there I wired a 'midi' plug to the 'video' out, to this I taped video & audio. also ran 3 wires to pin 3, 5 & 2...added a SPDT (center off) toggle... this sends 'audio in' to A: ground (noise free mode) B: no where (normal mode) & C: audio out (feedback mode) via a 500k pot. another c64 paddle... no full travel but good for a start...

It looks a bit funny with 5 C64 paddles but all the mods are on the outside, so I can test different units to see the different feedback effects... so far, feedback is a MUST DO & works better on the 8580 than the other 65** 9v chip

As the toggle is 'in line' with the video / audio cable...the feedback pot (c64 paddle) is tapped off the toggle...


hope that helps someone do a quick & easy setup...

Ktronik

Offline

 

#47 2008-08-30 01:53:32

InactiveX
The Last Ninja
From: England
Registered: 2008-08-14
Posts: 280

Re: Making Pots More Accurate

I've been experimenting with pots and caps since getting a C64 last week.

Assuming here that 12 o'clock is with the pot at zero, clockwise to increase. Using GetLoFi's scheme, the best results I've had are with 100K linear pots, and using 4700pF capacitors between the pots and pin 8 on the joystick ports. Under these circumstances I get maximum values at between 7 and 8 o'clock, whilst the pot's full rotation is at 10 o'clock. I am happy with this.

I also tried using 470K pots with and without 1nF caps at the same locations. The capacitors made little improvement, and the range of rotation was not at all good.

With things as they are now, I also get very little jitter, but there is some at the tops of the ranges.

These are the parts I used and recommend, from Maplin UK, if anyone's interested:

Part No. JM74R 100K Linear Potentiometer

Part No. NO6CN 4700pF Polypropolyne Capacitor

Offline

 

#48 2008-08-30 13:59:18

R64
Pac-Man
From: Melbourne, Oz
Registered: 2007-01-26
Posts: 222
Website

Re: Making Pots More Accurate

Nice one dude - great work.

Another thing to watch out for, is that some SID chips (which houses the A/D converter for the pots) don't get a full range. So if you're really stuck getting it to run well you could try swapping your chips around.

Offline

 

#49 2008-08-30 17:40:42

InactiveX
The Last Ninja
From: England
Registered: 2008-08-14
Posts: 280

Re: Making Pots More Accurate

I'll bear that in mind - thanks R64.

I've just got a second C64 - I'm new to all this - and get the same results as with my first C64. The two SIDs have similar manufacturing date codes: 32/84 and 40/84, although the first was manufactured in Thailand and the second in Korea.

I hope to be getting a SIS2SID soon and am looking forward to doing the stereo mods.

Offline

 

#50 2008-08-30 23:29:50

Cybertronic
Bub
Registered: 2008-07-28
Posts: 154

Re: Making Pots More Accurate

So one is only half suppressed by a powerful force (Korea) and the other might have a penis (Thiland)?

Offline

 

Board footer

Powered by
© Copyright 2002–2008