9 Pin Joystick To Usb Adapter
Aida Mazyck
I do not have a schematic so I'm just speculating. You have two separate wires for each ground input on the two separate ports. This is how it differentiates which controller input is pressed. Meaning basically that they aren't common ground, they are electrically isolated grounds, and actually a chip output. One thing you will learn in digital electronics is to never tie outputs together or you will damage chips. So more than likely what is going on is each ground is switched off and on opposite of each other at a high frequency.
So for example if you press fire on the Joystick A port, GND is cycling between low and high really fast. You have probably two NOR gates(depends really though could be an OR gate for active low instead of high I'm just speculating), one for Joystick A fire and Joystick B fire for the other joystick. And other NOR gates for the directions but I'm just using fire as an example here. So to trigger the fire for Joystick A, during the cycle when Joystick A ground is low, and fire is pressed that would make the output of that NOR gate high becaues both inputs are low(GND for joystick A, plus the fire input line going into that NOR gate for Joystick A), telling the computer that Joystick A fire is being pressed. The GND for Joystick B which is always an opposite level of Joystick A is tied into the other NOR gate along with the fire input line.
Without the diodes present you would be tying GND for Joystick A and B together(which are actually outputs not just a common ground) whenever two of the same buttons or same directions are pressed on the joysticks at the same time, which isn't good.
What I did here may make more since to some. You see that GND for each is a digital output for each and you don't want those to connect. If you press fire on each joystick at same time they will, or both downs, ups, and so ons. It will be bad for whatever circuit is swapping them low to high, you are shorting them out because while one is high the other will always be low.
Also want to reiterate that I'm not saying this is the exact setup on the TI99, this is what I would do if designing something similar, but I'm sure they have a similar setup of some type and I'm sure you need diodes.
I am pretty certain the diodes prevent one controller from interfering with the other as all of the control lines are tied together and polled using the power/return lines as selection.
However it is more to prevent damage to components I believe as apposed to one controller interfering with another. If you have 2 controllers pressing down, up, left right, fire at the same time or any other controller combination they really aren't going to interfere with each other more so than blow something if you do not use diodes. The two pins labeled for GND for Joystick A and B, are opposite high and low of each other at any given time(hence the polling you mentioned) and if you press fire or any other buttons that are same on the joysticks at the time you have one of those "GND" outputs in contact with the other while one is high and one is low, which would possibly blow something.
It won't blow anything. It's just to prevent crosstalk. Without the diodes the joysticks interfere with the keyboard scan and each other. It's the same situation as the Alpha Lock key preventing UP from working. (The joysticks are an extension of the keyboard matrix).
Yeah, I don't have a schematic I was just guessing, but yeah there would be a cycling and you are correct I'm sure, it probably goes to a transistor for each as well first before making it to the GND for each Joystick so instead each will cycle open, low instead of open, high but I didn't know for sure so to err on the safe side I figured I'd suggest the diodes, and my apologies to the other guy then because he was correct.
I can probably design a similar circuit with a 555 timer, a PNP and NPN transistor and it will work like you said to where each would be low/open opposite of each other to poll each controller going into a single port to have something to do for fun, and have an LED for each input for each controller. Like I said though not knowing the unit or having a schematic as far as I knew it could have been a chip output cycling from high to low for each, cause either would work but I should have known better that it was probably designed a little better than that. Thank you for the clarification.
Again I was thinking about how I would do it with an oscillating circuit using a timer chip I would need transistors because it would have a high/low cycle and if I wanted to do the same with the 555 I would need them for low/open instead. Everything would be internal on the I/O chip so I guess I was wrong when I said it probably had transistors for the outputs. Thank you for the links.
Looks like I was lying a lot and your instincts were better than I thought. While I know the keyboard side of it relatively well, I haven't directly interfaced to the joysticks much. I began to wonder when I remembered the 1-of-8 decoder, since that SHOULD have resulted in a high on the inactive pin. The schematics show that for the joystick selects only, the select signals run through a small circuit that changes them from high/low to open collector. The transistor is in fact there (along with a few resistors and a cap). Sorry about that! But that does answer one question for me anyway (that being "why is there no + voltage, anyway?") I guess TI was just trying to be cautious.
yeah i saw the transistors in the link you provided me in the pdf but they used two NPNs, the way I would have to do it with a single output alternating high/low to change to low/open alternating with two I'd have to use a PNP and NPN so they do have it designed different than I was originally thinking they would have.
I was thinking if two people press same button same time each controller it wouldn't matter as far as interference goes in the circuit like for example here with transistors low/open cycle, because the input would just see ground anyway and same button pressed on each controller anyway so why would it matter. But if the two cross they are seeing each others low at opposite halves of each cycle so it is basically like they are low constantly while each controller has same button pressed instead of low/open cycle, and even though the input on whatever chip will still see the input as low for each controller, it will not be at the low/open cycling it is expecting to see at whatever frequency and is instead seeing a constant low for whatever button was pushed and may cause some problems since it is expecting to see the low/open cycle for when a button is pressed for whichever input and not just constant on. So I can understand now how it may cause interference without diodes. I was more concerned at first with damage to components without them because I thought possibility of them each having a low/high cycle coming from a chip possibly(but that is cleared up now).
I picked up this joystick adapter recently for my detachable joystick model Odyssey 2 and it works perfectly. Highly recommend it to be able to use any Atari 2600-compatible controller with my Odyssey 2 and hard to beat the $16 price inclusive of shipping. Much to my surprise, they even included a second joystick adapter free of charge, though it's unclear to me if that was intended or not.
Yeah, the detachable joystick model is harder to find but they're certainly out there. Legend has it that that Magnavox got a lot of customer complaints about joystick failure and their repair department was swamped with joystick repairs, and since Magnavox felt the joystick failure was due to customers repeatedly yanking the joysticks out of the rear ports of the console, they revised the console to make the joysticks permanently attached.
Good rule of thumb is if the joysticks are silver in color, they are part of an early model detachable joystick console. The revised console with attached joysticks are always black with red fire buttons. Also, the bottom of the front of the console box of this early model will always say "The Ultimate Computer Video Game System...by Magnavox" NEVER "Odyssey 2. The excitement of a game. The mind of a computer." Note that that the former slogan being on a console box does NOT guarantee detachable joysticks, it's just that detachable joysticks will always have that slogan. Further, it's possible that resellers may pair early-gen consoles with later-gen boxes, but that's the general rule of thumb. Here's one example (not my listing).
Not a HUGE fan... But I live in a very small condo (with wife and son) and even though I have a lot of real hardware (most of it is in storage lockers) I like to use real controls with emulation or on the MISTer when I can.
Correct. I found them on eBay pretty cheap a few years back. I do have a pair of 2600dapters, but I also have the original Bliss Box when he made them by hand, then I got a Bliss Box 4Play. He makes the Blister for the Mister. I will probably get one some day, as I really like my case and already have the USB Hub.
I picked up a Wico Command Control Joystick adapter in a box of misc gear today, and was wondering how this thing actually works. It has a regular joystick pin connector that goes into a breakout box with two 9-pin joystick ports and it appears to be a digital to analog converter (officially for Atari-compatible Wico joysticks). I assume this means it would allow standard Atari joysticks to work with the 2e?
Software that uses the analog stick inputs to discriminate between "left, center, right" (and the corresponding states for the vertical inputs) could work with this type of adapter and a digital joystick. Any of the games with Lode Runner-style controls, for example. It would not work so well with flight simulators, or other software that uses the analog inputs actual value such as Dazzle Draw. My guess is that it simply uses pass transistors and fixed resistors to simulate the (left, centered, right) potentiometer states given the digital joystick switch positions.
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