Entering the correct combination on ths drive allows you to depress the button on the rear of the drive to extend the USB 3 plug for insertion into the USB port on a computer and look at the information contained on a 32Gb memory stick...

At least that is what everyone will think.. However entering the correct second 5 digit combination with the connector extended will allow you to access the secret 32Gb hidden drive within where the real information is stored.

That's 3 lines of defence

5 digit combination lock to extend the USB connector and look at the 32Gb drive contents
ignorance that a second drive exists
different 5 digit combination to access a hidden 32Gb drive

The shell protects the delicate electronics and inner workings from prying eyes. It is sealed with adhesive to prevent opening. The number rings are solid and the combination is hard coded.

Locking the drive is a simple matter of depressing the USB connector back into the housing.

Step 1: Void the Wty on Your USB Drives

I used 2 Kingston 32gb USB 3 type drives for this. I selected these for the local availability, size and price since I knew that I was going to be destroying them to make something great.

I pried the protective shell off to reveal the inner circuits.

These will both have to be modified by removing the VCC power pin from the circuit board. This is pin 2 in the case of the USB 3, 9 pin architecture. checking the datasheet for a connector will show this..

For sizing, one of the drive input connectors has to be removed... Carefully!!! I used a hot air style soldering iron for this and the connector literally fell off the board.

I used wire wrap style wires for this next part.

All of the drive pins connected together between the dummy and secret drives, with the exception of the power pin.

On the circuit board side of both drives there needs to be a wire connected to position 2, this is the VCC power for the drives. do not connect it to the power input from the USB connector it needs to be completely isolated from the power input.

A jumper wire is then soldered to pin2 of the USB connector. This wire will eventually feed the power back to the drives and also power the control circuitry, for now leave the power wires disconnected.

The mess of loose wires here has 6 wires not connected at both ends, 2 black 5V from the USB connector. 2 yellow for ground, and one white for power to each drive.

Step 2: Parts

Using the included files, print the parts needed for the drive.

There are 5 digit rings needed, 5 spacers, 2 end caps, 1 locking rail and 1 internal board holder

I have included 10 number combination rings here.

Step 3: The Digit Rings and Unlocking...

The digit rings have two unlocking features.

The first is the standard combination style lock which is just a space or opening in the inner ring.

The second is a bevelled lump which will provide mechanical input to the lock circuitry.

Step 4: Electrics, Circuit Description and Partial Assembly

I usually start the physical design first then make the electronics fit, this limited my choice of switches drastically and I had to use tiny tactile switches that were underrated for the tiny relay I needed to use.

to correct this I had to use the switches to drive a transistor to switch power for the relay coil to avoid burning out the switches which were rated for 1mA each.

The circuit uses the USB input power through 5 switches wired in series. There is a 1k resistor in series with the switches which drives a tiny transistor to activate the coil of a relay.

The relay in normally closed position will send USB input 5V to the dummy drive. When the switches are all closed and the relay coil activates, the relay will then shut off dummy power and apply power to the secret drive.

Each switch is held in place with adhesive in the selector ring as shown.

Each digit ring is then placed onto the selector ring taking care to slide the ring lump through the cutout. mind the orientation of the rings and note the opening combination.

It is easier to solder the switches together as each ring pair is glued to the next.

When all the rings are fastened together the circuit must be tested prior to final assembly.

Step 5: Mechanical Internals

The internal drive carrier is assembled as shown with an end cap and locking slide.

The locking slide has bevels on it so that the drive can be locked with the rings out of position.

Ideally the slide will have springs to hold it in place, I did use foam weatherstripping as a suitable replacement. The foam compresses to allow the slide to collapse and then springs back to its original position to pressure on the slide.

The rear of the carrier has a button cap attached which is the same colour as the housing. this has a flange to prevent the drive from retracting too far and also to prevent any physical access.

There are tabs for the USB drive to lock into place and a cutout for the relay.

The Dummy drive is placed in the cutout with the chip side down. a small insulation layer is placed then the secret drive is stacked on top of it. I used 2 side carpet tape.

These are all held in place using non conductive adhesive. I used hot glue but that is not an ideal solution.

Adhesive was also used to eliminate all loose and hanging wires.