Introduction

I previously made the remote mine and proximity mine from the movie and Nintendo 64 video game Goldeneye. The set would not be complete without the timed mine, so I spent many evenings designing and making the remaining prop.

It uses a rotary encoder to set the time, a 4 digit 7-segment display to present the time, LEDs to show the status, and a piezo buzzer to signal the countdown's completion. With many components in a small housing, I used a custom PCB for the electronics.

Materials and BOM

I reused many of the same parts from the previous mine builds.

PLA+

(1) Arduino Nano board

(8) 3/8" diameter x 1/4" height neodymium magnets

(4) 5 mm LEDs (blue)

(4) panel mount LED holders

(4) 120 Ohm resistors (0805 package)

(1) 150 Ohm resistor (0805 package)

(5) 10 kOhm resistor (0805 package)

(2) 10 nF capacitor (0805 package)

(2) SMD Headers

(1) Terminal Block

(1) 4 Digit 7-Segment Display

(1) Rotary Encoder

(1) Knob for Rotary Encoder

(1) Passive piezo buzzer

(1) SPST push button switch

Acrylic paint

Sandable filler and primer

JB Weld or similar epoxy

Krylon Matte Finish (1311)

I also used miscellaneous tools and consumables such as a soldering iron, wire, small gauge heat shrink, sand paper, and brushes.

CAD Design

The original CAD files were modified to have 4 equally spaced holes for LEDs, a hole for a rotary encoder, and a larger hole for a display. The LED and rotary encoder holes were straightforward, but the display needed provisions for mounting. Four posts were introduced and brackets were added so that screws could hold the display solidly in place.

Arduino Firmware and Circuit Design

The code was written for an Arduino Nano. It includes a driver for the chosen 4 digit 7 segment display.

Printed Circuit Board Design

Because of the small space inside the housing and the additional components compared to previous mine projects, the only way to get everything to fit was to use a printed circuit board. I laid out the circuit board in KiCad with a few key features.

1. First, I chose a 4-layer board to keep the form factor small without unnecessarily complex routing of traces.
2. Second, the display could be soldered to the board after it was fastened into the plastic housing.
3. Third, the Arduino Nano could be plugged into a socket. The socket allowed for soldering access to the display through holes.
4. Last, I wanted a connector block that all the wiring for the LEDs, rotary encoder, and power could easily plug into.

3D Print

All pieces were printed with PLA+. The lower housing and battery covers did not use support, while the upper cover did use supports.

Fill and Sand

Heavy coats of sandable primer were applied to the shells to fill the layer lines. The pieces were then sanded smooth with grits up to 600.

Paint

The pieces were painted with 4 coats of acrylic paint.

Clear Coat

Two coats of Krylon Matte Finish 1311 clear coat were applied to all the pieces.

Bond Magnets

The strong neodymium magnets were bonded to the shells using JB Weld.

Fasten Display to Upper Shell

The 4 digit 7 segment display was fastened to the upper housing using 4 screws and 2 3D printed brackets.

Solder SMT, Buzzer, and Connect Components to PCB

All the required surface mount resistors and capacitors were were soldered to the printed circuit boards. Afterward, the through hole connector block and buzzer were soldered.

Solder Display to PCB

The PCB was placed over the display pins which were just long enough to make good solder joints.

Solder Connectors for Arduino

Two 15 pin surface mount connectors were soldered to the PCB for the Arduino Nano to plug into.

Solder Wire Leads to LEDs and Rotary Encoders

Solid core wires were soldered to the LEDs and rotary encoders. Heat shrink was used to protect the joints. Likewise, connections to the 9V battery terminal and pushbutton switch were made.

Assemble

Components were inserted into their respective holes, and wires were plugged into the connector block. The Arduino Nano was also inserted into its sockets.

Enjoy

Like the other mines I've made, I made 2--one for myself and one for my brother who enjoyed Goldeneye as much as I did.