Here are a few details about the 'disc load' and 'disc in' signals of the slot loader and how I have them working with the 'open/close' signals the Hitachi drive uses.
Every slot loader I've seen uses some form of optical sensor to detect the disc, this drive uses Reflective Sensors that are slightly staggered as ya can see here..
All these things are is an Optocoupler/Photocoupler, but it has to have something pass over it to turn on the Transistor part of it, so they're just switches when ya get right to it, the same thing used in a tray loading drive, just works a little differently is all. The first one is the 'disc load' and when the disc passes over it tells the drive to start the loading process, this translates to the same thing as ya pressing the tray on that type of drive and it starts to close on it's own.
The second sensor is the 'disc in' and is also used as a 'stop' sensor for when the disc is ejected, if the first sensor were used for both it would have to push the disc out that far to uncover the sensor and by that point the disc has fallen on the floor, likewise if the second sensor was used alone the disc would eject properly and sit like it's supposed to, but you'd have to force it in the drive to that point and that's no good either. To complicate it just a tad more both of these signals have to be used on one line to 'tell' the Logic board what state the 'tray' is in, so we need to get these 2 sensors to work together while doing different things.
There is also a 3rd mechanical switch on this drive that is used after the disc load cycle is complete, when a disc is inserted and it's run the full course of loading it up and getting everything out of the way this switch gets closed, ya can see it in the top right corner here..
Now the Hitachi uses 2 mechanical switches to tell where the tray is at. When the tray is open both switches are open (High), when the tray is closed both switches are closed (Low), when the tray is opening/closing one is open while the other is closed.
Now it was pretty obvious that the one switch of the Hitachi jived with that 3rd mechanical switch of the slot loader, when the tray is all the way in the one Hitachi switch is closed, when the disc is fully loaded in the slot loader that switch is closed, perfect match so nothing needs to be done there at all but to wire it up.
The Reflective Sensors though are the trick as they both have to be wired up to the same signal line and basically act as one switch to take the place of the other mechanical switch of the Hitachi. Since we can't just use one or the other, I guess ya could if ya liked your 360 to puke out discs onto the floor, we need to rig it up so this first sensor does it's job and then buggers off, enter the 555 chip that has more uses than ya can count. I used the OneShot Monstable circuit to be triggered off the first sensor there and then it's output is run to an NPN Transistor and acts as the second switch. Put the disc in the drive and it 'sees' it, the OneShot triggers and pulls the signal line low, this is the same as pushing on the tray of the Hitachi and causing the one switch to close so it starts to close the tray. This pulls the disc in and loads it, then finally closes the mechanical switch which is the same as the tray being closed all the way, but do ya see the problem here?
That alone doesn't cut it because after the OneShot times out the Transistor is turned off and the signal line goes High again, same as if the switch were open, but that can't be because if ya recall the Hitachi thinks the tray is opening/closing if one is open and the other closed, so here's where the second Reflective sensor comes into play.
It's wired up with a couple of Transistors, thing didn't want to work on it's own for some reason, but regardless it's used to take over holding the signal line Low when the OneShot times out, so that line stays Low like it should. This Sensor is also used when the disc is being ejected as when it's uncovered the signal line goes back to being High, same as if the tray hit the end of it's open cycle and the switch were opened, and the disc hangs there waiting for you to do something with it.
Now ya may be asking why use the OneShot in the first place since that signal line just has to go Low for it to work, good question, but remember that the line also has to go back High again to let the Logic board know that the tray is open all the way. If ya had both of these Sensors wired together on ejecting the disc it would have to clear both Sensors before it returned the line to the High state and stopped, but like described before using just the first Sensor causes the disc to be spit out onto the floor, not very kool. What the OneShot does is lets us use the first sensor to detect ya want to load the disc so it starts the process of 'pulling in the tray' then before it times out the second Sensor is covered and take over holding that line Low. Then the OneShot times out and does nothing, even if it were trigged over and over again it's not going to make any difference as the second Sensor is doing all the work now, so the OneShot is pretty much in there to use that first Sensor just for that one moment, then it's forgotten about until the disc is removed and is ready for the next disc to cross it's path.
Here's the schematic of the setup I used, the first Reflective Sensor (RS1) and OneShot are in Red while RS2 and it's circuitry are in Blue. The Sensors aren't drawn in the schematic but go Low when activated.
This post has been edited by RDC: Nov 22 2008, 03:59 PM
WIP Slot Loading Dvd Drive, Hitachi + iMac + A LOT of Time/Work = ???
Nov 18 2008, 04:20 PM
