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.

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