Originally Published: TUESDAY, JUNE 23, 2015 AT 12:10PM
Making a 3D-printed Sonic Screwdriver
In addition to the Tardis, the sonic screwdriver is probably the object most associated with The Doctor. The sonic screwdriver is a sort of all-purpose device that acts as a sensor, emitter, and interface to electronics. Its signature function, however, is its ability to unlock (almost) any door. When I realized that I could use a keyfob to make a sonic screwdriver that actually unlocked doors, I knew this was going to be my next project.
This sonic screwdriver is modeled on the most recent prop used in the Dr. Who show, commonly referred to as “the eleventh Doctor‘s sonic screwdriver”, though it is not exclusive to the 11th doctor. I didn’t have actual dimensions for the prop or any of the various toys and replicas that are commercially available. However, there is abundant reference on the internet and I attempted to make my screwdriver close to the actual prop without trying to exactly match every detail. I did not use actual measurements, proportions may not be quite correct, and the overall size was constrained by the components I used inside, and is thus significantly larger than the actual prop.
In addition to a recognizable outside (which I will refer to as the case), I had a few requirements:
- a green light that turned on when a button was pressed.
- a sonic screwdriver sound effect plays in a loop when the same button is pressed.
- the sonic screwdriver can unlock doors at my office via the HID card readers.
There are several guides to making a sonic screwdriver, each with a slightly different set of functionality. I didn’t find any that were exactly what I wanted to do, and most had more complex electronics for sound effects than what I settled on. I found this instructables guide most inspiring but still not particularly applicable to my design.
Since my sound effect was sufficiently simple I was able to use Adafruit’s Audio FX Sound Board. This saved me a lot of time and is quite small for a microcontroller with its capabilities, but it was still the limiting factor in how small my sonic screwdriver could be (it is noticeably larger than the actual prop).
- A sound file to play (The one I used is here, adapted from this Youtube video).
- A speaker (I bought this one, and this one also looked promising). It’s surprisingly hard to find a small enough 8 Ohm speaker.
- A green LED (I got this pack of 100. Nice because it comes with the appropriate resistors and is available in other colors)
- A button. I got a set of these to play with
- An Adafruit Audo FX Sound Board. This little board is surprisingly versatile and incredibly simple to use. No coding, bootloading, or complex wiring necessary. I would highly recommend this for a large variety of prop type projects.
- A battery. It has to be at least 3 Volts (I tested with up to 4.5 Volts) and be able to provide enough current. Three 1.5 V watch batteries in series were not enough. I used a battery very similar to this duracell battery.
- Some wire, a soldering iron, electrical tape or heat shrink
- Paints. I used acrylic paints from Golden Paints for the metalic colors (“Iridescent Copper” and “Iridescent Pearl”) and Blick brand acrylics from the Blick art store for the matte colors (“Mars Black”, “Emerald Green”, and “Titanium White”. I’m sure you can find similar acrylic paints at a local art store or online.
- A 3D printer (I used a Form 1+).
- There are 3 stl files: case top, handle, and handle base. There’s also a Form file if you want to print on a Form 1+.
- A Key Fob (or other RFID type chip) that already opens the door you want your sonic screwdriver to open.
- A heat gun (if you’re going to mod a keyfob, see section 3 below)
- An OnShape account (if you want to modify the case models. At the time of writing you can sign up for free access to the beta but it takes about a day to get activated)
1. Print The Case
Print out the sonic screwdriver components. I used a Form 1+ with Grey Resin. If you wish to make changes to the models, the OnShape document is here. An account is required, but you can sign up for a free account and then access, view, and copy that document to make your own changes.
One modification you may wish to make is adding holes for the speaker. The speaker is quite loud outside the case, but once the screwdriver is all closed off it’s much quieter. You may want to add some holes to the upper case before printing, or you could try drilling them after.
The effects board would barely turn on when I had the LED in series with it. Presumably there was too much of a voltage drop. So I just wired them in parallel. You do have to have a battery that has sufficient current to drive both circuits.
The wiring diagram is as follows:
It will be difficult to wire everything up first and then get everything in the case. Nevertheless, it might be useful to see the actual components wired together, so here’s an image:
Assembling the components, perhaps with minimal soldering, could also be useful for testing that you know how everything goes together, but keep in mind that if you do this you’ll have to take it apart to perform the final assembly.
3. Fob Key (optional)
My office has standard HID fob keys. The full key does not fit inside the sonic screwdriver, but I discovered that it is possible to roll these fob keys to make them small enough without breaking them.
Split open the case by running a razor blade along the seam and prying it open. One side is just the case, the other has the electronics (a wire coil and an incredibly tiny chip) and the other side is just a case.
Cut off the loop and, very carefully, the excess plastic around the coil. Wire snips cut through the soft plastic very easily. Still, if you break any of the incredibly fine wires in the coil, the fob will no longer work.
Test that the fob key still works with your door. Now use a heat gun to heat the plastic until you can start to bend it. It’s easier if you wear a heat-resistant glove because then you can continue to apply heat while bending the plastic against a surface like a tabletop. The plastic should soften but not melt. Be careful to not overheat or bend too sharply. I recommend bending in small increments and testing the key fob after each manipulation. If you accidentally cause one to stop working, you’ll get a feel for how much stress it can take.
I was surprised by how resilient thes fob keys were, but the more distorted they are, the shorter their range is. I went through a few before I was able to get one that fit in the screwdriver and still activated the door through the case.
4. Sound FX Board
Perhaps the best part of the Sound FX board is how easy it is to load sound files. Connect it to your computer with a micro-USB cable and the board mounts as a standard USB drive. Then you can drag and drop the file through your system’s file browser.
My file is
T02HOLDL.wav which means it will play on a loop (
L) while pin 2 (
T02) is connected to ground (
HOLD). Adafruit has a much more detailed discussion of file naming and loading in their product tutorial.
NOTE: Some cheap micro-USB cables will deliver power to a device (e.g. for charging) but do not have the data lines necessary to actually move files to and from the device. If your Sound FX board does not appear as a USB drive when you connect it to your computer, you probably have one of these power-only USB cables. Adafruit sells a micro-USB cable.
For my circuit design I wanted the sound to play whenever the Sound FX board had power, so solder a wire connecting ground and pin 2.
Solder the resistor to the annode of the LED (the longer lead), then add lead wires that are long enough to reach through the sonic screwdriver. The ground wire needs to reach the battery ground, so should be longer than the fully assembled screwdriver, and the wire connected to the resistor needs to reach out of the top section of the screwdriver and connect to the lead coming off the button.
Once the LED is wired, push it up from the inside throught the hole at the top of the screwdriver. I applied some super glue around the edge of the hole from the outside to hold the LED in place.
2. Keyfob (optional)
Insert the keyfob or equivalent into the top section of the screwdriver case. Be sure to test that it still unlocks the door from within the screwdriver. Once you’re sure the position is correct, find some way to secure it in place, such as glue or tape.
Since the Sound FX board only goes in the bottom of the handle section of the case, make sure that the speaker leads will reach out of the top section of the case and through the handle section. This way you can thread the leads through the handle section and solder them to the Sound FX board while it’s outside the case. Glue the speaker in place inside the top section of the case. At this point the top section of the case should have the two speaker leads and the two LED leads coming out of it.
Solder one wire to one side of the button, long enough to reach out of the handle and attach to the battery. Solder two wires to the other side of the button. One needs to reach out the bottom of the handle to provide power to the Sound FX board. The other can be shorter: it only needs to go out the top of the handle and get connected to the LED’s lead. The button sets in from the outside, so put the wires through the hole that will hold the button, thread them out the appropriate openings, and place in the button. Use some glue to hold the button in place.
5. Final Connections
Solder the speaker leads to one of the amplifier channels on the Sound FX board.
Solder the Anode lead wire from the LED to the short wire coming out the top of the handle from the two-wire side of the button.
Solder the long wire from the two-wire side of the button to the Vin hole in the Sound FX board.
Connect the lead wire from the single-wire side of the button to the positive terminal of your battery. Connect the Sound FX board’s ground pin and the LED’s cathode wire to the negative terminal of your battery.
I didn’t have good contacts for the battery and was getting impatient, so I soldered directly to the battery. This was both difficult and dangerous (because lithium batteries can catch fire and/or explode). It would be much better to use electrical tape to hold contact pads (e.g. pieces of conducive tape) that are in turn soldered to the wires. If you do try to solder to the battery, I found I hald to scuff up the negative end with a file before the solder would stay on. This, too, was probably a dangerous solution.
6. Finish Assembly
Test that everything works now that you have it all wired together.
Carefully push the Sound FX board into the case handle, curl the excess length of any wires and push them into the case, then connect the three pieces of the case. Mine press-fit together nicely, without modification, but you could sand them if they’re too tight or add some glue if they’re too loose.
I applied accrylic paint directly onto the printed part. I had to apply two coats to the silver parts and several coats to the white handle. You could spraypaint with some primer first, which would help the paint last and perhaps require fewer coats.
Here’s an image of my fully assembled, painted screwdriver.