Recently I published an instructable for gathering Rare Earth Magnets From Old Hard Drives. In the comments section, Ventifact made a comment that the platters from the HDD would make good Heliographs.
One definition for heliograph is "a signaling device by which sunlight is reflected in flashes from a moveable mirror."
That got me thinking about signal mirrors and how well the platters would work for that purpose. While the platters will work right out of the drive as a signal mirror, there is room for improvement.
Changes I decided to make:
1) add instructions on how to use a signal mirror, in case someone never has.
2) add a way to attach the mirror to other gear
3) protect the mirror finish for when it is needed.
Signal mirrors are a great survival tool because they are light weight, easy to use, never run out of batteries, don't rely on radio or cellular signal to work, and they work at tremendous distances.
I found a youtube video that claims to be a signal mirror working at a distance of 43 miles. While I can not verify the distance, it is obvious that the signal mirror can be seen from an amazing long distance.
Step 1: Tools
Platter(s) from a Hard Drive - it's a good idea to have more than one in case mistakes are made
Drill and bits
Packing Tape - We will get to this in a little while
Proper protective gear is always a good idea. For this instructable I can not stress how vital they are (hence the bold print). Keep reading, I'll explain.
Step 2: Danger Will Robinson
I wanted to attach a split ring to the mirror to make it easier to attach it to other gear. In order to do that I need to drill a hole in the platter to pass the split ring through.
As I have mentioned in previous Instructables, the platters inside hard drives are typically made from either aluminum or glass/ceramic that is coated in aluminum.
The problem is they look exactly the same, and until you start drilling into the platter it is difficult to differentiate one from the other.
As you can see the first two platters I tried to drill were coated glass and they shattered ( yes that shard popped up toward my face before landing back on the scrap wood I was drilling on. the larger shard flew off onto the patio table).
The third platter I drilled was aluminum. Now that we have a platter with a hole in it we can proceed.
Step 3: Instruction Label
In case anyone is wondering, circle label templates come in many sizes. 3.75" diameter is NOT one of those sizes, at least not that I could find.
I was able to find a template for 3.3" diameter which actually worked out great because that gave me room to attach the label to the platter without gluing it.
Step 4: Poor Man's Lamination
Grabbing the packing tape mentioned in the "Tools" step, it is time to make that label one with the platter.
Take the time to apply the tape carefully to avoid bubbles.
Tape past the edges of the platter will make it easier to line up the tape, it also helps to avoid any fingerprints on the sticky side of the tape.
Anyone that has ever handled one of these platters can tell you that they will attract dust and fingerprints like nobody's business. Adding a layer of tape to the mirror side will help to prevent scratches and keep the dust and fingerprints to a minimum. If you are ever in a situation where you need to use the mirror to signal, you can use it as is or you can peel off the tape and have a pristine mirror surface to work with. It will work either way.
If for some reason the mirror side gets badly scratched or otherwise damaged, you can always peel the instruction label off of the back side of the platter and use that side to signal with.
Step 5: Adding Bells and Whistles
I added a bit of gutted 1100 paracord as a lanyard.
I was wiping off the mirror before calling it done, and I realized that the lens cloth was just the right size to make a pouch to keep the mirror in.
A few quick passes on the singer sewing machine and my signal mirror now has a fancy protective sleeve that will clean it off without scratching the finish or leaving lint behind.
Step 6: How to Use
Hold the mirror (instruction label towards you) close to your eye and look through the hole in the center.
Hold your other hand up making a "V" with your index and middle finger, arm fully extended. (peace sign)
Sight on your target so it is between the "V" of your outstreched hand.
Move the mirror side to side so the reflected light from the mirror is passing back and forth over your fingers to signal your target.
You want to move the mirror for two main reasons.
1) a flashing light is more noticeable than a steady reflected light
2) you want to get the attention of the person you are signaling .. not cause them permanent retinal damage.
If you need to use the signal mirror, in a non hostile environment, don't be discouraged if you don't see any signs of civilization. Sweep your light from your signal mirror along the horizon.
Signal flashes can be seen even when you cannot see the aircraft, boat, or other means of rescue.
Modern distress signals are based on groups of three. A distress signal can be three fires or piles of rocks in a triangle, three blasts on a whistle, three shots from a firearm, or three flashes of a light, in succession followed by a one-minute pause and repeated until a response is received. Three blasts or flashes is the appropriate response.
If you want to signal using Morse code, SOS is three short, three long, three short, signals. . . . - - - . . .
Illustrated images from: