Joy2BPlus question on modding a Genesis gamepad

[iscariot]

Hey, I was looking at the Joy2Bplus project and I saw a Quickshot genesis pad for $1.  I popped it open and looked at it, and it looks like it's a little different from a regular genesis pad.  The chip in this one is the M74HC157BI.  The pic of the genesis pad in the github has a marking for a chip marked 74HC157 on the PCB.  Are these one and the same?  I'd like to use this pad with my 800XL

[TGB1718]

The 74HC157 is a Quad 2 channel multiplexer, generally the extra letters signify ratings/package etc.

for use in a Joypad I don't think the type would have any bearing as long as you have the same physical

device

[iscariot]

What do you mean?  Sorry I've not done this before.  The innards of this controller is different--looks like the PCB has provisions for extra buttons. I can post a pic if that helps

[TGB1718]

Pictures always help 👍

[iscariot]

1 hour ago, TGB1718 said:

Pictures always help 👍

Here we go:

 

Note the extra pads on the PCB.  I'm guessing that Quickshot has a one-size-fits-all approach to wiring their controllers.  This is a Starfighter 3B controller BTW.  The controller shell is in 3 pieces, the back, the front, and this bezel that has the buttons.

[iscariot]

I was reading the github...do I need resistors if it's a genesis pad?

 

[TGB1718]

If your wanting to use more than 1 button, then I believe the "extra" buttons use the "POT" inputs on the joystick

port, if that's the case, then for those inputs I think you will need resistors to switch between a high resistance and

a low resistance when the button is pressed, you might have to change the values on that board as I think they are

too low a value.

 

For UP/DOWN/LEFT/RIGHT/TRIG there is no need for any resistors

[iscariot]

Yeah, I have those three buttons, I was thinking about making them work.  I need to get ahold of some resistors then.  Does that chip look like the same as the genesis one?  If so, what do I need to solder?  Just put the resistor in line with the wire?

[TGB1718]

For the Atari I don't think you need the chip, as for using the POT's as triggers, you need 

to rewire 2 X 1 Meg Ohm resistors to +5V, the other end of the resistor to POT A and the other to POT B.

The extra trigger switches each need to be wired across the 1 Meg Ohm resistors so when pressed

short the resistor out.

 

The UP/DOWN/LEFT/RIGHT/TRIG just need 0V connecting to one side of each switch and the other side

to the appropriate pins on the 9 pin D

 

Edited August 26, 2022 by TGB1718

[iscariot]

Ohhh Ok.

15 hours ago, TGB1718 said:

For the Atari I don't think you need the chip, as for using the POT's as triggers, you need 

to rewire 2 X 1 Meg Ohm resistors to +5V, the other end of the resistor to POT A and the other to POT B.

The extra trigger switches each need to be wired across the 1 Meg Ohm resistors so when pressed

short the resistor out.

 

The UP/DOWN/LEFT/RIGHT/TRIG just need 0V connecting to one side of each switch and the other side

to the appropriate pins on the 9 pin D

 

 

So basically the resistors are there to pull down the voltage across those two buttons?

[TGB1718]

58 minutes ago, iscariot said:

So basically the resistors are there to pull down the voltage across those two buttons?

No, the POT circuit is a C/R circuit, the charge on the capacitor is sampled by POKEY at given intervals and the voltage

converted into a number (can't remember the MAX/MIN values) but in the range 0 to 255.

 

The larger the resistance, the lower the voltage will be on the capacitor due to the longer charge time (5 * C * R for full charge)

and obviously lower resistance, the higher the voltage. Once read, the capacitor is discharged and it starts all over again

[ascrnet]

5 hours ago, iscariot said:

So basically the resistors are there to pull down the voltage across those two buttons?

please read the wiki to have your questions answered. 😉

[iscariot]

On 8/27/2022 at 2:20 PM, ascrnet said:

please read the wiki to have your questions answered. 😉

Yes, I am.  I have the schematic up, as well as the pictures, the problem is that the controller image of the mega drive controller is a little confusing.  It looks like the 74HC157 chip is removed, and then pin 1 is jumped to pin 13, and then 9,10,11,12 are all shorted to each other, but I'm looking at a zoomed image.  Is that correct?

[ascrnet]

9 hours ago, iscariot said:

Yes, I am.  I have the schematic up, as well as the pictures, the problem is that the controller image of the mega drive controller is a little confusing.  It looks like the 74HC157 chip is removed, and then pin 1 is jumped to pin 13, and then 9,10,11,12 are all shorted to each other, but I'm looking at a zoomed image.  Is that correct?

Now I understand your doubt, if they removed the chip and the photo does not look very good. Now I updated the git to put the reference to the forum where the change is applied and with better photos. I also put it here. 😉

[iscariot]

Thank you.  So it looks like pins 9 and 11, and 10 and 12 should be shorted...cool.  I plugged it in last night and it was telling me that it found a button three--hopefully this will resolve everything.

[ascrnet]

perfect, take pictures and tell us when it works so we can put it in the git and link it to this topic for people who find themselves with this same gamepad. 😉

[iscariot]

OK, well shorted the pins, and it shows buttons 1,2, and 3.  However, 3 isn't working despite being shown, and both left and right aren't working either.  I'm going to pull the controller apart and have a look at it.  Here's pics of what I did:

 

 

[ascrnet]

8 hours ago, iscariot said:

OK, well shorted the pins, and it shows buttons 1,2, and 3.  However, 3 isn't working despite being shown, and both left and right aren't working either.  I'm going to pull the controller

okis, I understand what happens is that it is not reaching the exact value for button 3. for this write this in Atari BASIC should give you as default value 228, and when you press the button three the value 1.

10 PRINT STICK(0),PADDLE(0),PADDLE(1):GOTO 10

there won't be two resistors in parallel ?

[iscariot]

Thanks.  What about L/R not working?  Did I get a bit of solder some place?

[iscariot]

OK, well I jumpered some of the pin holes and I have L/R/U/D as well as button 1 and button 2, however, I can't get the third button to work.  When I plug in the modified controller, and run the BASIC code above, it shows the second button sits around 19, and then jumps to 228, the third button sits at 1 no matter what I do.  I tried jumpering the pins, and soldering in a resistor, but neither worked.  I noticed that the voltage across the second button is like 3.5v, but the voltage on the third button is 5v.  Sorry I'm not as good with a multimeter as I probably should be here.  This particular controller was using a slightly different chip.

[+playsoft]

I have limited h/w knowledge, but this is how I converted my Mega Drive controller for joy2b+ use:

 

https://forums.atariage.com/topic/278884-2-button-joystick/?do=findComment&comment=4410098

 

The first step was to swap the wires coming from pins 5 & 7 around. The A8 provides +5V on pin 7 but the Sega controller expects it on pin 5. Also, pin 5 on the A8 is the paddle B input, which is what the third button uses.

 

It was easy to swap the wires on the Mega Drive controller as they are numbered on the pcb. You can't see them in the after picture but the green and light brown wires in 5 & 7 are swapped around.

 

[iscariot]

59 minutes ago, playsoft said:

I have limited h/w knowledge, but this is how I converted my Mega Drive controller for joy2b+ use:

 

https://forums.atariage.com/topic/278884-2-button-joystick/?do=findComment&comment=4410098

 

The first step was to swap the wires coming from pins 5 & 7 around. The A8 provides +5V on pin 7 but the Sega controller expects it on pin 5. Also, pin 5 on the A8 is the paddle B input, which is what the third button uses.

 

It was easy to swap the wires on the Mega Drive controller as they are numbered on the pcb. You can't see them in the after picture but the green and light brown wires in 5 & 7 are swapped around.

 

THanks.  I'm looking now.  However, this isn't an "official" mega drive controller, it's an aftermarket and uses a different chip, so there is some weirdness.

[iscariot]

On 9/8/2022 at 5:30 AM, playsoft said:

I have limited h/w knowledge, but this is how I converted my Mega Drive controller for joy2b+ use:

 

https://forums.atariage.com/topic/278884-2-button-joystick/?do=findComment&comment=4410098

 

The first step was to swap the wires coming from pins 5 & 7 around. The A8 provides +5V on pin 7 but the Sega controller expects it on pin 5. Also, pin 5 on the A8 is the paddle B input, which is what the third button uses.

 

It was easy to swap the wires on the Mega Drive controller as they are numbered on the pcb. You can't see them in the after picture but the green and light brown wires in 5 & 7 are swapped around.

 

THanks.  I'm looking now.  However, this isn't an "official" mega drive controller, it's an aftermarket and uses a different chip, so there is some weirdness.

 

Ok..I think I know what I was doing wrong--is there a pinout for the controller if you're looking into the controller connector on the controller and not the console?

[iscariot]

Ok, I think I have been looking at the wrong thing.  Is this correct:

 

 

[+playsoft]

Yes, that is the Atari pin-out.

 

The megadrive pin-out looks like this:

 

 

If you haven't swapped 5 & 7 around, when plugged into an A8 your controller will be drawing power from the paddle B input - which is what you want to connect the 3rd button to.