analog joystick readings

[+grips03]

Today I use the multimeter to record Atari 5200 analog resistance:

 

pin 9 to pin 11

up = 16k

center = 280k

down = 426k

 

pin 9 to pin 10

left = 12k

center = 280k

right = 416k

 

I was wondering if up could be zero ohms and down could be infinite ohms?

 

This would reduce the parts needed for digital controller PCB.

 

 

[+grips03]

I went back and centered up the pots usings Pete's cart and looks like 350K - 380k is more in the center of the screen.

 

I think the Atari has a pot on the system to adjust as well. Is that under the front panel near the led?

[bohoki]

its easy enough to just make 500kohm the downs and rights if you let it go infinite the center drifts in some games i made a post about the actual triggering ohm ratings on various games

 

many games are different

 

what i did was wire in a 500k pot and just slowly rotate it till i got movement then turned off the system and used a multimeter

 

here is my h-value of some games so centered stick is anywhere between max for left and minimum for right all values in k ohm

max resistance for left|center|min resistance for right
gyruss 70||484
popeye 71||390
montezumas revenge * 1||427
wizwor 112||351
space invaders 124||365
digdug 128||394
pengo 172||367
choplifter 267||317 this one has a very tight center
kangaroo 186 323
berzerk 176 444
galaxian 152 351
pacman 153 394
ms pacman 183 322
mariobros 140 421
mr do* 1 470
centipede 155 349
pole position 172 298 very tight center
joust* 1 434
buck rogers 118 436
defender 98 453
qix 117 386

these are the absolute position games so i just locked down a dead center
super breakout 259k
missile command 260k
kaboom! 233k

Edited October 7, 2013 by bohoki

[+grips03]

its easy enough to just make 500kohm the downs and rights if you let it go infinite the center drifts in some games i made a post about the actual triggering ohm ratings on various games

 

many games are different

 

what i did was wire in a 500k pot and just slowly rotate it till i got movement then turned off the system and used a multimeter

 

here is my h-value of some games so centered stick is anywhere between max for left and minimum for right all values in k ohm

 

max resistance for left|center|min resistance for right

gyruss 70||484

popeye 71||390

montezumas revenge * 1||427

wizwor 112||351

space invaders 124||365

digdug 128||394

pengo 172||367

choplifter 267||317 this one has a very tight center

kangaroo 186 323

berzerk 176 444

galaxian 152 351

pacman 153 394

ms pacman 183 322

mariobros 140 421

mr do* 1 470

centipede 155 349

pole position 172 298 very tight center

joust* 1 434

buck rogers 118 436

defender 98 453

qix 117 386

 

these are the absolute position games so i just locked down a dead center

super breakout 259k

missile command 260k

kaboom! 233k

thanks for posting this. Are some really 1 or 1k ohm? they have a * next to them.

Edited October 7, 2013 by grips03

[foft]

The pot inputs charge a 0.047uF capacitor from 5v through - at least on atari 800 - on the 5200 there is a pot common line I believe is also 5v. The pot values read are the number of scan lines it takes to charge the cap from 0v to around 2.2v (Schmitt trigger input - see pokey data sheet).

 

One approach for a digital solution would be to do something like the Atari touch tablet. It rests at 1.8v then charges to 2.3v after a delay! So if you are reading a digital stick you convert the position to a delay.

[+grips03]

right now I'm going to use an analog switch, mapped into the resistance reading I got from the Atari controller. I'll make sure to at least cover the games listed above.

 

I might make another version that converts analog 10k pot joystick (think PS2 type controller). This version would be self centering and provide full analog support. Plan is use Arduino to analog read the 10K ps2 joystick type joystick and then i2c to a digital resistor with values to keep the Atari happy.

Edited October 7, 2013 by grips03

[bohoki]

the pot common provides enough power to light leds and run autofire circuits in my adapted pc joysticks

 

also when you use pin 12 for the pot common the system treats it like a trakball so i have a switch on one of my homemade sticks

[foft]

also when you use pin 12 for the pot common the system treats it like a trakball so i have a switch on one of my homemade sticks

Can you explain this please? I thought pot common was 5v with a variable resistor in the 5200 to fine tune. So I'm not sure I understand how the 5200 can tell if using pot common or 5v. Is it that pot common is enabled only when the stick is selected?

[+grips03]

I got my digital pcb today and tried some resistors, so far I like:

 

up/left = 59k

H/V center = 280k

down/right = 499k

 

Right now design uses 2x DG413, 7404, 7432, 7408. Plan is to switch the 74xx logic to a CPLD to reduce parts. It would be cool if CPLD could also be the analog switch that selects the right resistor. There are 6 resistors on the board, two of each size above. Keypad and fire 1 & 2 run directly as they don't need any logic or different resistor values.