Introduction: Mjolnir: Thor's Hammer!
Summon the lightning and thunder as only Thor can! Or at least wield something that is really bright and really loud.
Parts & Qty
Thor Hammer x1 (Adult hammer preferred)
Momentary pushbutton x1
PVC end cap (threaded) x1
PVC to male thread x1
Lock washer x2
SPDT switch x1
Computer speakers (active speakers) x1pr
LiPo battery, 12V, larger than 500mAh x1
XT-60 male adapter x1
Heat shrink tubing (assorted sizes) x1 set
Prototype board (minimum size: 5cm x 9cm) x1
Arduino (Pro) Mini x1
LM2596 Voltage regulator set for 5V output x1 (or similar)
DFPlayer Mini (not MP3-TF-16P) x1
Micro SD Card x1
IRL (logic) type MOSFET x2
*Acrylic sheet (1/4" to 1/2" thick) Custom size (see bottom of list for selection considerations) x2
Small pieces of acrylic for mounting, 1" wide 3" long, x4
Leather or Leather-type fabric, 1-1/2" wide 18"-24" long
3/8" Threaded rod coupler x2
Black or gray hinges, 1-1/2" long x2
Bolts that fit hinges and speakers (black) x12
Nuts that fit bolts (any color) x12
Hook up/lead wire kit, 22ga solid tinned x1 set
Resistor, 10k Ohm x1
Resistor, 1k Ohm x1
LED, 10W x4
1/2" x 1/2" Heat sinks x4
Safety glasses (it's at the top of the list for a reason)
Spray paint (metallic grey)
Black paint or paint pen
Solder 63/37 .020"
Solder braid or pump
Helping hands with magnifying glass
Contact glue (E6000)
Clamps, minimum 2
Aluminum foil (optional)
Laser engraver or other etching means
Bandsaw or jigsaw
Sewing machine (if needed for handle strap)
Hot glue gun
Hobby knife set
Ruler or measuring tape
USB to TTL serial cable (or similar)
Audacity (freeware) to edit sound files
How to (de)solder
How to tin a soldering tip
How to use a sewing machine (or know someone who does)
Basic understanding of electricity
(V=volt) (A=amp/ampere) (W=watt)
Basic knowledge of circuit components (to identify amplifier parts)
Power tool safety (specifically bandsaw or jigsaw)
*Acrylic unit weight per square foot: (12" x 12") or per 30cm x 30cm:
1/4" (6mm) thick = 1.4 lbs (.65kg)
3/8" (9mm) thick = 2.1 lbs (.97kg)
1/2" (12mm) thick = 2.9 lbs (1.31kg)
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Step 1: Have an Idea Turn Into a "Go Big or Go Home" Moment
Not sure this project could be considered easy after looking at the long list of parts, tools, and knowledge. This whole endeavor started out with my wife wanting to dress up like Black Widow for a (family friendly) company Halloween party about 5 years ago. You know, do something nice for the kids. I had no issue with that...until she wanted me to dress up as Thor. You see, I hadn't fully embraced my inner nerd at that time. So I got the costume and Mjolnir (the hammer), but I felt like something was missing. If I'm the god of thunder, then I wanted some lightning and thunder. So the idea was born.
Well, time constraints limited me to poster board cutouts and spray paint. It was a little unwieldy since each piece was 3 feet long making the entire thing about 6-1/2 feet. So the Halloween party came, the kids loved us, and it was over. The hammer and costume went into the closet, but the thought of summoning lightning and thunder lingered. As fate would have it, the area I currently live in hosted its first comic con, and so I went because I'd never went to one. I wore a simple Superman shirt with a small cape on it. I was amazed at some of the other costumes I saw, and then I became determined to do better next year.
Step 2: Turn the Idea Into a Proof of Concept Circuit
I learned some electronics knowledge and soldering skills about 15 years ago that I dabbled with from time to time. The basic concept I wanted was LEDs flashing and some speakers playing thunder. However, I wanted to see lightning - not blinking lights. This led me to searching the Internet which led me to some really great Instructables. I wanted bright/flashing lights to edge light some etched acrylic, and the 20W LED-Strobe developed by einyaa seemed to meet those needs. I had never worked with an Arduino and coding before, but the Instructable provided enough information to stumble through it. I purchased the parts and built the circuit. I even managed to tweak the code to generate a random number of blinks on the LEDs. ***WARNING: This produces a very bright light that you should not look directly at without shaded eye protection (or point it away from you).*** See the before and during pictures above.
However, this only got me part of the way. I still needed thunder, and I had a microcontroller that I thought should be able to be the brains of syncing light and sound. I scoured the Internet for syncing light and sound. Didn't find much that was helpful until I just searched for lightning and thunder. Then I found the Instructable by davebodnar for lightning & thunder in a castle for a model train layout. He did a very detailed Instructable that I only had to tweak to meet my needs.
I also used the IRF540N MOSFET/LED combo from einyaa (it works but not for the right reasons) versus the IRL520 MOSFET (use this one or other suitable logic-level MOSFET) that will also work with the 20W LED array. The pinouts are the same for both. I bought a few IRLs that should be arriving soon to swap out. The "L" designation is for logic - the MOSFET gate opens fully at 5V (output of microcontroller) with minimal heat generated in the MOSFET. My lightning only flashed for 14 seconds, and I didn't have an issue with heat from the 10V gate on the IRF540N that only receives a 4-5V signal from the microcontroller. Any longer though, and I can't tell you what will happen. Better off sticking with a logic-level MOSFET.
I wanted very loud claps of thunder so I took apart a pair of 3W computer speakers that already have an amplifier built in (also called 'active speakers'). I found the necessary connection points for the DC voltage on the amplifier board since a batter only puts out DC voltage. You can figure out the amount of voltage needed by looking at the speaker wall wart. It should have a sticker showing the output (ex: 12VAC or 7.5VDC). To get DC voltage (VDC) from AC voltage (VAC), you need a bridge rectifier. If the wall wart isn't already DC, then the amplifier board has 4 diodes (small, black cylinders with a stripe on one end). I used a multimeter to find the output of the rectifier and soldered in new, sturdier wires. I had to order the DFPlayer Mini (has DFPlayer Mini written above the SD card slot and not MP3-TF-16P). The latter is a cheaper version that I couldn't get any of the 3 I bought to work (hardware or library issue). I couldn't find any 1GB - 8GB micro SD cards that were cheaper than a 16GB micro SD card, so I bought a 16GB card. Maybe I can use it in another project or expand the sound library on the hammer.
For the thunder, I used Audacity (freeware) to edit a thunder file and load it on the micro SD card. The file has to start out with 0001 (needs 4 digits), but you can add an underscore and extra after it (eg. 0001_thunder.mp3, 0002_roar.mp3, etc). Also make sure to copy the files to the SD card in the order you want them to play....something about file allocation. Audacity may not be the simplest program, but it is intuitive enough to figure out how to at least clip and convert a sound file.
I used a LM2596 Voltage regulator set for 5V output, but you can use any 12V to 5V converter than can handle at least 2 amps. I had connected the LiPo battery to the RAW pin on the Pro Mini, but it fried the circuit during testing and troubleshooting (oops). Now I run 5V to Vcc. The LEDs and speaker amplifier were both 12V.
With all the pieces gathered, I set up the circuit on a breadboard. Forgot to take a picture, but it finished looking roughly like the above Fritzing picture. The DFPlayer Mini has an internal 3W amplifier built in that can drive a speaker. I wanted something a little more powerful so I connected the computer speaker amplifier signal inputs to the DAC_L and DAC_R pins. I couldn't get any lightning when I sampled off the DFPlayer DAC pins to A0 and A1 on the Pro Mini. After talking it over with a buddy, we figured that the DAC outputs don't provide the same strength signal as the SPK output (internal amplifier). I moved the sample wires back to SPK_1 & SPK_2 and it worked. You could also try reducing the values (666 & 750) in the code to find the right setting, but I was in a hurry to finish.
Below is (or should be) the code I used. Tested and tweaked it once everything was on the breadboard.
Step 3: From Flashing to Lightning
Still with me? Hopefully. So far all I had was a flashing light with some speakers. A quick Internet search found plenty of info on etching acrylic/plexiglass/polycarbonate. The 10W LEDs have about a 1/2" wide surface so I figured anything from 1/4" to 1/2" should work. Went to a local shop that cuts custom pieces of anything from acrylic to wood (searched for 'plexiglass supplier'). After hearing about the project, they were happy to donate some scrap from the drop bin. I needed a 12" x 12" piece but got a little more than that. The only thing they had though was 1/2" thick piece. This stuff was challenging to work with. I'm looking at 1/4" or 3/8" the next time I edge light acrylic.
I have a friend with a 25W laser engraver that was excited to see the final product. I picked out a lightning pattern I wanted, and he converted it into a file he could etch on the acrylic. TIP: Find a picture first, then add a rough outline around the lightning careful to avoid angles a bandsaw can't cut. My hammer has a 4" face, so we made the base of the lightning 3" wide and extend 5/8" so I could mount some other acrylic pieces to hold it in place. TIP: Weigh your pieces after you cut them so see how much support is needed. After 3 passes, the laser would not cut all the way through the acrylic. However, it did very nicely on getting a deep etch of the lightning using full power and half speed. The outline roughly followed the shape of the lightning, and we put some slight angles in there to throw light in more directions. We tried using a coping saw to cut out the shape, but it generated so much heat that the acrylic fused back together. We had way more success using a bandsaw. Then, I sanded the edges with a belt sander. TIP: Try to avoid points and sharp edges on the lightning as this stuff can do real damage if it accidentally bumps into someone (especially kids).
Step 4: Preparing the Hammer and Handle
Please keep in mind that most of this was done the day before the comic con and extending into the wee hours of the morning. It isn't pretty, but it worked.
I cut the hammer apart using a hacksaw blade because I didn't have access to a power tool at that time. Looking back, I'd probably cut just the top out so I can place everything inside without having to add a hinge, nuts, and bolts. Either way, don't use a hacksaw. It was an ugly cut. Used some small black nuts & bolts to secure the hinges (and later the speakers). Scored the plastic surface of the hammer with some sandpaper where the magnets & coupling nuts would be located so the glue would stick better. I found it easiest to stick the nut onto the magnet to get an idea of where to mount them. Used a lot of contact glue to secure the coupling nuts and magnets to the inside of the opening. Clamped them down for a bit while I worked on other things. Later ran a bead of hot glue later just to make sure they won't come off.
Laid everything out into a configuration I was happy with and marked the outline of the speakers. Cut out and smoothed small openings to allow sound to project out. Using hot glue, I covered the openings with the computer speaker covers that I cut down and painted metallic silver. There was a plastic mesh on the speaker cover that I trimmed down with wire cutters and carefully peeled back some extra material. Then I mounted the speakers using more of the black nuts and bolts.
I used hot glue to mount the amplifier board to the top of the hammer to decrease the amount of wire needed to run to the speakers. Soldered the Pro Mini, DFPlayer Mini, resistors, and MOSFETs onto a 5cm x 7cm prototype board. Cut out a small rectangle using a hobby knife to fit the on/off (SPDT) switch on the bottom of the hammer where the handle mounts. This switch turns the main power to the circuit on and off.
I drilled a hole in the threaded part of the handle and the recessed portion of the hammer with a 3/8-in drill bit. I used a hobby knife to shave off and smooth the opening to as large as it could go. NOTE: You only need to do this if you want to run the battery charging cables to the bottom of the handle. You can make a smaller hole if you just want to run the pushbutton wires. At this point, I feel obliged to remind you that testing the circuit is a good idea before continuing.
I used a hacksaw to cut the very bottom of the handle. I took the handle with me to the hardware store and found a PVC to male-threaded adapter and a female threaded end cap. Sorry, don't remember the sizes, but the adapter was a very tight fit. Still glued it in place though.
Used a Dremel to grind down some ridges on the end cap and created a diamond pattern with a few dots. Doesn't need to be perfect since most people focus on the hammer. Just needs to give the impression of something that is not a PVC pipe fitting. Some threads were showing after I screwed on the end cap so I used the Dremel to grind the exposed threads. Spray painted the PVC metallic grey after roughing up the surface with sandpaper. Then I dabbed a black paint pen in some of the holes and smeared it around with a cloth to give it some contrast.
I had a friend sew some studded material into a strip that I attached with a bolt, flat washers, lock washers, and nuts. It'd also work with a leather strap, but I couldn't find any free/cheap pieces. A dab of plaint paint covers up the bolt and washers nicely.
Then there was the 1/2 inch acrylic lightning bolts. That was a challenge. They were heavy so I opted to glue two 1in x 3in pieces to the base of the lightning so I could mount it on the inside of the hammer. I made sure everything was flushed before I glued and clamped it. While those were drying, I cut a 1/2in notch into the bottom part of the hammer and a small notch on the top piece. I used a scrap piece of acrylic to make sure the lightning would fit. Once the glue dried, I dry fitted everything and trimmed the top part of the hammer a little more so I could get it closed. Then, I glued and clamped the lightning pieces into the hammer....and waited for it to dry.
To finish the lightning, I used duct tape to secure the LED arrays to the acrylic because hot glue wouldn't hold it. I removed any excess tape on the acrylic surfaces and put aluminum foil on it with spray adhesive to prevent light from escaping. You can probably use the aluminum tape but make sure you cover the LED array with electrical tape to avoid shorting the wires. Heck, to be honest, you probably don't even need to cover it at all since the LEDs are so bright.
Step 5: Have at Thee Knave!
As 3 a.m. quickly approached, I turned off the hot glue gun and soldering station. There wasn't much more I could do before I got up at 7 a.m. I was really impressed with how it turned out considering I had to figure it out as I went along. The lightning/thunder caught a lot of people off guard...or maybe it was the hair. Meh, who knows.
This was my first in-depth Instructable. Going to submit this for the Halloween contest. If you like it, then hit the vote button please. I gladly welcome any comments, suggestions, and questions below.
Participated in the
Halloween Contest 2018