Techno-geek Roulette (or Who Makes the Coffee?)




This is a gadget made from recycled computer parts to give an absolute, unequivocal and irrefutable answer to that eternal office question - "Whose turn is it to make the coffee?" Each time the power is turned on, this wonderful device will randomly select a person to do the coffee-run.

Step 1: Bits and PCs

You will need the power supply unit (PSU), CDROM drive and a blanking plate from an old computer - The older the better. Also, a blank writable CDROM, a selection of small tools, a glue gun and a way of decorating the CD. If you're after accuracy, a protractor too.

The blanking plate is the 'L' shaped bit of metal you take out when you put a plug-in card in the PC. If you're like me, you've probably got dozens lying around until you actually come to need one - then you can't find a single one.

The CD drive must be a read-only type. Some drives work better than others for this. If you have a couple of old drives available, power them up in turn with a blank writeable CD in and see which one spins for longest before stopping. This will be the best drive.

The best type of blank CD to use is the type with a matte white topside which you can print onto with an inkjet printer. If you don't have printing capability, you could use permanent ink marker pens or enamel paint.

Step 2: Preparing the Power Supply

It's best to do this first, as the PSU will help us later. The simpler the power supply the better as more recent ones are harder to get working out of a system. The type which has a 20 way large connector is ideal.

Unplug all the power connections inside the computer and remove the power supply unit. You will usually find three screws on the back panel of the PC holding it. Once out, blow hard into the ventilation holes to remove the dust of ages.

Now you're into the PC, you can take out the CDROM drive (usually a couple of screws into the side) and a blanking plate from the back panel.

If the large connector from the PSU has a green wire in the position shown in the photo, connect a wire link to it, and to one of the black wires next to it. This is the lead which would go to the power switch and needs to be grounded to turn the supply on.

Step 3: Hacking the CDROM Drive

There are many, many different models of CDROM drive, but they are all put together in roughly the same way. Your drive may not be exactly like this, but it won't be too different.

What we want to do is to remove the cover and tray of the CD drive so we can see what's going on inside the drive. There is a low power laser in there, so don't look directly down on the assembly when it's running. Once we've got the disk on the laser light will be blocked.

With the PSU connected, turn on the supply and eject the tray. Turn off and disconnect.

Turn the drive over and remove the four screws underneath. Ease the bottom and the wrap-round top cover off the drive. Keep the flat bottom panel - we'll be using it again later.

Remove the tray. It may come out if you bend the middle upwards, or you may need to cut a plastic clip or two with wire cutters. Once you're done, it should look like the fourth photo.

Step 4: The Disk of Destiny

This is where you can unleash your creative talents. Mine are minimal, so I used the CDROM printing software which came with my Canon printer and a bit of clipart.

The important thing here is dividing the disk into the right number of segments. You can either eyeball it like I did, or use a protractor to get the exact angle for the lines. Divide the number of names into 360 to get the angle (e.g. 5 people is 360/5 = 72 degrees).

We are using a blank writeable CD so that the drive is aware that there is a disk in there, but can't make sense of it. It spins and spins, and eventually gives up, leaving the disk in a random position.

Note : Canon Pixma printers sold in the USA have the CDROM printing function disabled and do not include a tray, but you can enable the CD printing with the help of THIS instructable, and get a tray from eBay, or make one like THIS . (I'm in the UK, so mine was already enabled ;¬)

Step 5: Putting It All Together

Use cyanoacrylate glue (superglue) to attach the decorated CD to the drive spindle. We want the disk to sit flat, and hot-glue is too bulky for this. If the spindle isn't in the right position for the disk to spin freely, you may need to find the arm or plate which moves it. Don't force anything. Once you find the right part it should move easily and lock in place. The fourth photo shows where mine was. You may need to power up the drive and press the open / close button to get it to the right state.

Once the disk is attached, this button is going to be a liability, so carefully 'disable' it with a pair of wire cutters (and the power turned off).

Bend the blanking plate so that one end sits over the top of the drive, and the other just overlaps the disk. Cut it to length at the back, and draw on the arrow with a marker pen. Hot-glue the pointer in place (third photo).

Using more hot glue, stick the flat plate from the case to the back of the drive. This will give you a flat surface at the back. Now glue this firmly to the PSU so that that the pointer is pointing down (connector at the top) and the whole assembly sits solidly on the table.

You could cut off all the wires from the PSU except the ones to the drive. If you do this, you will have to cut and strip the green wire and then twist it together with a black wire. This should then be insulated. Make sure the other wires are cleanly cut with no stray whiskers.

Or you could drape and glue the wiring looms and connectors to the drive itself to make things look more interesting, like I did. Use the hot-glue gun for this.

Step 6: Who Makes the Coffee?

To work the gadget, leave it plugged in but with the mains wall switch turned off. At coffee time, turn on the power and wait with bated breath to see whose name stops under the pointer. Turn off the wall switch.

If the disk stops precisely on a dividing line, coffee duty will be decided by a round of 'rock paper scissors' between the two people indicated.

The selected person must now go and make the coffee, or, in the case of those unfortunate enough to have one, persuade the drinks machine to produce a beverage which is almost, but not quite, entirely unlike coffee.

As the Kaptin says below, this isn't limited to coffee making. With different disks you could replace throwing a dice, play roulette, make vital life decisions etc. Your imagination is the limit!

(Some drive motors seem to have a couple of dozen angles they prefer to stop at. If you're thinking of using more than ten or so sectors, don't use one of these as it will skew the randomness. You can feel it as a lumpyness when you turn the disk by hand.)

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    37 Discussions

    I'm thinking of doing this for a school project and I need to do a scale drawing and I'm not sure of how?


    9 years ago on Step 6

    Hey i have tried this but it didn`t last long as the cd drive fried if you know a sollution to this please email me back at Thanks that would be great

    2 replies

    Reply 9 years ago on Step 6

    Must have been a dodgy drive you were using which would have failed anyway. This isn't making it do anything it's not designed to do. It's just using the normal cycle it would go through if an unreadable disk is put in it. Try a different drive.

    dark sponge

    10 years ago on Introduction

    " produce a beverage which is almost, but not quite, entirely unlike coffee"

    -The Hitchhiker's Guide to the Galaxy

    I absolutely love that book!

    6 replies

    Reply 10 years ago on Introduction

    Yep, it was tea; I paraphrased the great Mr Adams. And machine tea is always at least infinitely worse than machine coffee. To keep that brain cell working it has to be the 'real thing'. (And I dont mean Coke - although that statement could open up a whole new box of frogs ;¬)

    dark spongeAndyGadget

    Reply 10 years ago on Introduction

    Oops, I forgot. I read the book awhile ago, and can't remember some of the details. Yes, it was tea.

    " produce a beverage which is almost, but not quite, entirely unlike tea"


    10 years ago on Introduction

    not sure if it has been said but you should mark a pointer on the cd tray inside the computer put the disk in and after a couple seconds open the drive and look where it is


    10 years ago on Introduction

    Could you the "Roulette" Inside your machine? By attaching the wires of the PSU to the cd-rom drive i think it's possible. Everytime it tries to read the disk, it starts spinning :)


    10 years ago on Introduction

    Suggestion - Get some little magnets and glue them on the dividing lines on the wheel (North pole facing outward). Now glue another on the pointer so that as the wheel spins this magnet (North facing in) repels the ones on the wheel. If the wheel stops near a line, the repulsion of the magnets will move it one way or another, guaranteeing no arguments. To be really sure you could put another magnet (South facing in) a bit away from the pointer so the wheel would stop in the middle of a segment. Magnets would have to be weak enough or far enough away so they did not prevent the wheel from starting when the power was turned on. To overcome the unevenness when slowing down (which you mentioned), you could increase the inertia by making the wheel heavier, and also allow some slippage between the shaft and wheel, or, after finding more preferred stopping places (eg 12) than people, divide the wheel into 12 segments, and mark some of them "spin again"...

    1 reply

    Reply 10 years ago on Introduction

    Thanks for the magnet idea, but I think I'll stick to 'rock scissors paper ;¬) It's only some motors which have the preferred stopping points - most don't. The one I used in the project has 24, so the six segments have 4 each. I aligned the disk so it couldn't stop on a divider. Actually, if the number of stopping points is not exactly divisible by the number of segments, it would be a way of biasing the result {evil grin}. If you use the more common motor type with no preferred points, this won't be an issue. The 'spin again' idea is a good one if you want a fair wheel and have the wrong number of people (and only that type of drive).

    my shop teacher used one of these to decide what would happen to you if you came to his class tardy.


    10 years ago on Introduction

    If this is a "pointless" contest, I'll vote.