Wednesday, November 30, 2011

Alarm clock project 1: initial opening and beginning research

This is the first post.
Second post: cutting
Third post: installing buttons and final look

My one complaint with my alarm clock is that the off button is very small. This is the button that turns the alarm off in the morning after it has gone to snooze a couple of times. So naturally you would want it to be big and accessible like the snooze button. But it's not. I thought it would be cool to modify the clock and add a big ol' mash-and-be-done button in its place and just solder the electrical connections to where the original button was. (Later I decided to throw on a bigger button for snooze while I'm at it).

Here's a bunch of the parts after it has been taken apart. The circuit board for the buttons was on the top, but you had to get to it from the bottom, so out comes everything in the way. Namely, the main "motherboard" and the CD player components.

And here's the rest of it! I still need the alarm clock, so I'm using the main circuit board while I'm working on this project. I have to use headphones and the clock's headphone jack since there's no speaker attached anymore. With the volume turned up they are loud enough to wake me up. The clock runs fine without the CD player attached. There's a transformer that takes the house current down to something reasonable, but it's still unnerving to handle a big messy open circuit that's plugged into the wall outlet...

Some inspirational parts:

On the CD player this gear is mounted by this unique piece of plastic (the curvy piece with three parts/arms). It's thin and designed to be flexible so that if the CD read head is driven too far and jams, this part shifts and flexes instead of breaking the gear.

This is how the radio tuner works. It shows which station you're on by this white, plastic-rubber piece. It curls up around the tuning wheel, to which it is attached. It curls and uncurls as you turn the wheel, moving right and left.

Here's a limit switch that has two flat, bendable contacts that are pressed together by a lever when the CD cover closes.
This is the opened position.

Closed position.

A similar switch on the CD player assembly. It's the black and clear plastic extending down from the circuit board in between the two motors. The two metal contacts are visible.
Open position.

Closed position.

Initial Project Pictures

Here is the front of the clock showing the size of the buttons. The button tops are a two plastic molds that press on small tactile switches.

Here is the power button area. I've drawn reference marks on scotch tape stuck on the clock. The paper is a stencil of the circuit board that goes underneath.
The shaded area with the X is the only area I can cut and put a button into. There is only a quarter of an inch of depth underneath that (the same size as the grid on the paper). This is not very big compared to what I had in mind, which was to cut away nearly all the available material underneath the power button and put a big ol' button there. Because of structural components that can't be cut away and the button circuit board's ribbon cable, that shaded part is all I have to work with.

I decided that's not enough and I'd have to find a different solution. There weren't any good buttons available that would be as big as that space but not very deep. I also didn't want an unsightly skinny or tall button. I began to think of other places were I could put a button and rout wires to it.
I realized that I could put a button right into the middle of the CD cover. I could leave out the CD player assembly and have lots of space to work with. I never listen to CDs on this clock anyway. Now that there's tons of room, I'm going to put another button for snooze.

I picked Adafruit's new arcade style buttons because they're cheap and look great. They're translucent and have room for an LED, so I might fit one inside and wire it to the button leads so that it lights up when pressed. Hopefully there will be the right kind of current to run the LED.
My other button option was this more boring one from Digi-key.

The total depth that extends down from underneath the button lip is 31.7 mm (from the details tab on the product page). It does not extend far enough to reach where the main circuit board is mounted. I've checked with the circuit board in place and there's tons of room for the button and routing the wire.

Here's another view. The short post is for mounting the CD player and the tall post is for mounting the main circuit board. The penciled line is the limit.

So now I will plan out the size of the buttons and where I'm going to mount them. Then when they come in I'll  inspect them more, cut the holes, mount them, solder them to wires and solder those to the contact points of the original buttons.

Friday, November 25, 2011

Taking apart a CD drive

A computer at home broke its CD drive, so after a new one was bought and installed, I nabbed the old one. I hoped to find interesting things inside and maybe I could use some parts for future projects. I'm researching and thinking about how I might use the moving frames as part of a plotter or something like that. The stepper motor and the moving frame for the CD read/write head could be pretty useful. Here are some pictures and descriptions.

All the main parts laid out, as viewed from the back of the drive (probably should have made them all face the camera :P ). The circuit boards are mounted underneath the cream-colored plastic frame, and the black CD tray slides into tracks on the top of the frame. I've taped the front cover of the drive to the tray for convenience and to keep track of it.

This next picture is the main mechanism for opening the the CD drive and sliding out the tray.

As you might expect, the tray is driven out by a rack and pinion. The driving pinion gear is the large black one in the upper corner. It is driven by a motor that normally pokes up through the curved, U-shaped space visible in the center (this drives the smaller black pulley with a rubber-band like belt).

The white plastic bar is instrumental for multiple things. When it is all the way to the left or right, the tray itself interacts with it and pushes it into the pinion gear, which moves it further. But then it gets moved out of the reach of both the pinion gear and the tray. It sits in one position or another (all the way right or left) until the tray moves the opposite way, interacts with it again, pushes it into the pinion gear, which moves it back the other way. More pictures of this later.

The CD read/write head and spinning motor frame is partially visible here (hereafter called the "rocker frame" for lack of a better name, because of the following description). This actually swings/falls down and away from the tray when it moves out. The front mechanism also involves this motion. When the white plastic bar moves sideways, it moves the rocker frame up and down. There are nubs in the frame that stick into the curved grooves in the white bar. These S-shaped grooves are also partially visible, since the rocker frame is in the down position.

If the CD drive jams, a paperclip can be poked through a hole in the front to open the tray. I've always wondered what it pushes inside. It goes through the square hole on the left and pushes the stubby, left-facing-L-shaped, white piece of plastic, which swings and pushes the white bar to the side by the straight bar it's a part of.

The small green circuit board is for burning LightScribe disks. They have tops that text or images can be burned into, I think with a laser.

A clearer overhead view of the front mechanism.

Here is a picture that includes a bottom view of the CD tray (as if it was flipped up). Here you can see the grooves that interact with the rest of the drive. This picture is annotated below.

The red parts interact with each other at later times than the blue parts. I'm not exactly sure when or in what way, exactly. But at the ends of the highlighted grooves in the tray there are angled parts that move the nubs on the white bar, so that's the basic idea.

A front view of the drive with one of the circuit boards laid into place. The previously mentioned piece of plastic that the paper clip pushes on is close to the hole now.

A view of the front mechanism circuit board. The center black square with the two buttons sticking up is used to see if the tray is fully in or out. See the next picture.

In the middle you can see those two buttons. They normally poke up farther through the cream-colored plastic frame if the circuit board was attached completely. The rectangular tabs on the white bar slide over the buttons and depress them in certain positions. The upper tab is close to one of these buttons in this picture.

A bottom view of the rocker frame, with the CD read/write head and spinning motor.

The rocker frame attaches to the main frame here with latches holding onto short axles for when it swings away from the CD tray.

The rocker frame taken out. Note the two black nubs mentioned earlier, now facing the bottom right corner of the picture. See the next picture.

Those nubs fit into these S-shaped grooves, also mentioned earlier.

A close up on the motor and screw gear that move the read/write head. I believe this motor is a stepper motor because it needs to be precise and because there are four electrical connections to it.

Here's a view of the read/write head. It's a precisely balanced laser with a lens. Notice the wires and silver metal blocks which appear to be magnets. I believe this is how the lens is precisely positioned.

Another view of the  lens.