Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2613806.
This is a remix of Intentional3D's excellent Portal Gun:
https://www.thingiverse.com/thing:1100601
Video of remix in action: https://youtu.be/80xivC-9lMo
I modified to fit an Arduino Nano (using emccarron's nano mounting base) and added mounts for the Adafruit 7 Segment display but the original mounting is still available as well. Also, I split the handle from the base so each could be printed on a 200 x 200 bed separately and then glued together. I've also affixed tabs to the corners of the base and top to alleviate warping if printed in solid ABS. Finally, I've counter-sunk the top screw holes for beveled machine screws.
My version is powered by dual li-poly cells via a mini dc-dc converter module set to 5V.
The Nano program is my own original work due to the different display, arduino, and rotary encoder I used. I haven't decided whether to provide the source code. The reason is because I would also have to provide schematics for wiring which would bring out the electronics and SE geeks to "correct" my evil DIY methods. I kind of think that a major part of the enjoyment for these kinds of things is the innovation to figure out things for yourself and to customize for your own idea of how it should work. At any rate, here's a list of the components I've used for this particular build:
Arduino Nano: I used a clone that I don't even think is V3 so probably any Nano will work as long as the pins are standard, which I'd think they'd all be.
DC-DC Converter: https://www.amazon.com/gp/product/B01MQGMOKI/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
Display: https://www.amazon.com/gp/product/B00GJRW0DS/ref=oh_aui_detailpage_o05_s01?ie=UTF8&psc=1
LEDs: https://www.amazon.com/gp/product/B01CI636JU/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
Rotary Encoder: https://www.adafruit.com/product/377
Knob: https://www.adafruit.com/product/2056
Plastic LED Bevel: https://www.adafruit.com/product/2171
Batterys: This style but any similar will work (x2): https://www.amazon.com/gp/product/B01MQE0SI4/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
10/31/2017: Included Wiring Schematic. 03/01/2018: Included PortalGun1.ino