# MacGyver Season 1 Episode 17 Science Notes: Ruler

Propane tank flame thrower

Take a propane tank and bicycle tube. Cut the bike tire to make it a hose and connect it to the propane tank. Use a road flare to light the gas—boom. There is your flame thrower.

Oh but wait. It’s just a dream. Bozer’s dream. The flame thrower wasn’t real anyway.

Listen in on a landline phone

Who uses a landline now anyway? Oh well. They want to use a landline then it’s possible to listen in. Actually, this isn’t even that difficult. Check it out.

Here is another version.

You just need a capacitor and maybe an inductor. You could grab these from a radio or something like that.

But wait. I made a mistake. While going over this hack, I said something like this:

“Yeah, this is pretty easy. Just get the capacitor and earpiece (or radio) and then tie it into the wiring box”

Here’s what that looks like.

I just want to point out this small mistake (that you would never notice) just in case you saw it. You don’t actually “tie” the lines—that’s just a term we use in circuits to mean “connect”.

Bomb radius calculation

There’s a bomb in the truck. Where should you park it so that no one gets hurt? Yeah, this is a tough calculation. However, tough has never stopped MacGyver before and it won’t stop him now.

Here is my rough calculation and explaination.

Bombs are complicated. But usually it is the pressure produced by the explosion that will get you. We can come up with some pretty useful models to calculate their impact. First, there is the Hopkinson-Cranz Scaling Law (this is a real thing). With this law, the acceptable distance can be calculated based on the explosive weight.

$\mathrm{Range} = (z)(\mathrm{weight})^(1/3)$

In this expression z is a factor that depends on the type of distance with 14.8 being the distance factor for a public traffic route. That means that 2 kilograms would need 18.6 meters (60 feet).

Infrared face jammer

OK, it doesn’t actually jam your face. That would be weird. MacGyver wants to prevent the security cameras from recognizing their faces. So he takes some infrared TV removes and pulls out the IR LED lights. Normally these flash on and off so that the sensor on the TV can “see them” but humans can’t.

He mounts these IR LED lights on some sun glasses with a battery to power them. When a security camera sees the face, it just gets blinded by the IR light since many video cameras can also detect IR.

If your phone camera doesn’t have an IR filter (most now do) then you can actually see the light flashing on a TV remote by pointing it at your phone.

Oh, so this could really work. It just depends on the type of video cameras. Some people even put stuff like this on their car license plate so that police cameras can’t see them.

Car jacking

How do you open a locked car door? One way is to jam a wedge into the door. This will pull the door out just a little (by bending it) so that you can get a stick in there. The stick then can be used to push the “lock” button.

In this case, MacGyver uses something for the wedge—maybe a shoe horn or a door stop. Then a monopod is extended to click the lock button.

DIY soldering iron

You might have missed this one. But as MacGyver is building his stuff for the last mission, he needs a soldering iron. He takes the heating element out of a hair dryer and connects it to some stuff. That works.

Fake noses

Need a disguise? How about DIY latex to make a nose? Yes, this seems plausible. Here’s how to do it.

DIY keypad cracker

MacGyver makes a quick circuit board that can crack a keypad by using a brute force method that goes through all the combinations. This is from a different episode, but it’s the same idea.

If you want to play with one yourself, here is an online version of the code.

DIY police radio

Well, it’s just a radio. MacGyver needs a speaker and a transmitter. Really, a radio transmitter is essentially the same thing as a radio receiver—OK, not really but sort of.

Instead of going over the way MacGyver did it, how about a real actual radio you could build yourself? Here is a spark gap transmitter from simple parts (and awesome).

Here is a more detailed explanation of the spark gap transmitter from one of my WIRED posts.

# Adventures in Spark Gaps

I wanted to build a spark gap transmitter—you know, for fun.  However, things didn’t start off so great.  Here is how it went down.

My first plan was to build this.

I like it, but it uses an ignition coil and some other thing.  However, check out the receiver.  That’s awesome.  It’s a coherer receiver (I think) and it basically detects a spark with those two bolts in the plastic sleeve.  There should be some iron filings or something in between the bolts.  When a spark is detected, the filings jump the gap and make it a conductor.  I’m not sure why the LED light is connected to a 9 volt battery though.

After that, I just did some google searches for spark gap transmitter and attempted to build the designs I saw.  None of them had capacitor values, so I just had to guess.  But they didn’t work.

I honestly thought I knew how to do this.  I tried a step up transformer with a capacitor.  Nope.  Actually, I was getting a spark on the battery side but not the step up voltage side.  How did I even pass physics courses?

Here is my attempt with a transformer.

Finally, I found a page that used an electromechanical bell.  That works.

I decided to build my own oscillator from scratch.

Homework (for me)

• Make this more solid (the connection to the steel plate is iffy.
• Could you replace the steel plate with a paperclip?
• Can you change the buzzing frequency by adding weights to the oscillating bar?
• Use a step up transformer to get BIGGER SPARKS.
• What about an antenna?
• Build a coherer detector.