# Genaille’s Rods: When Paint Sticks Do Math

What is a hacker, if not somebody who comes up with solutions that other just don’t see? All the pieces may be in place, but it takes that one special person to view the pieces as greater than the sum of their parts. As [Chris Staecker] explains in the video below the break, Henri Genaille was one such person.

When French mathematician Edouard Lucas (himself well known for calculating the longest prime number found by hand) posed a mathematical problem at the French Academy, a French railway engineer named Henri Genaille developed the rods we’re discussing now.

Genaille’s Rods are designed to perform multiplication. But rather than require computation by the user, the rods would simply need to be laid out in the correct order. The solution could readily be found by just following the lines in the correct pattern. This might sound a lot like cheating, and that’s exactly what it is. No manual math needed to be done. Genaille also created rods for doing long division, which we’re sure were every bit as enthralling as the multiplication rods. Demonstrations of both are included in the video below.

While Genaille’s Rods have gone the way of the slide rule, we can’t help but wonder how many engineers and scientists carried around a set of marked up wooden sticks in their pocket protector.

If designing and building manual mathematical machines is something that you think really adds up to a good time, check out this post on how to design and build your own circular slide rule!

# Polar Planimeter Quantifies Area By Plotting Perimeter

These days it’s hard to be carry the label “maker” or “hacker” without also being proficient in some kind of CAD- even if the C is for Cardboard. But before there was CAD there was Drafting and its associated arts, and one couldn’t just select a shape and see its area in the square unit of your choice. So how could an old school draftsman figure out the area of complex shapes? [Chris Staecker] introduces us to the polar planimeter, a measuring tool created specifically for the purpose and explained in full in the video below the break.

The polar planimeter being discussed is a higher end unit from the 1960’s. Interestingly, the first polar planimeters were invented in the early 19th century even before the math that describes their function was completed. A lever is placed in a fixed position on one end and into the planimeter on the other. The planimeter itself has another arm with a reticle on it. The unit is zero’d out with a button, and the outline of the shape in question is traced in a clockwise fashion with the reticle.

What makes the polar planimeter capable of measuring in multiple dimensions is the fixed arm. The fixed arm pivots around, allowing the planimeter to track angle changes which affects the output. So, the planimeter isn’t just measuring the length of the perimeter, but the size of the perimeter. The final measurement is output in square inches.

Overall it’s a really slick tool we didn’t know existed, and it’s fascinating to see how such problems were solved before everything could be done with a mouse click or two. Be sure to check out this 100+ year old reference set to round out your knowledge of past knowledge. Thanks to [Zane] for the great tip!

# Fixing A Broken Bandsaw With A Custom Steel Part

When a large bandsaw broke down due to a cast iron part snapping in two, [Amr] took the opportunity to record the entire process of designing and creating a solid steel replacement for the broken part using a (non-CNC) mill and lathe.

For those of us unfamiliar with the process a machinist would go through to accomplish such a thing, the video is extremely educational; it can be sobering both to see how much design work happens before anything gets powered up, and just how much time and work goes into cutting and shaping some steel into what at first glance looks like a relatively uncomplicated part.

# Speech Synthesizing Valentine From 1991

Back in 1991, a young [Backwoods Engineer] and his new wife went to a Valentines day get together. One of the conditions of the shindig was having the guys make – not buy – a Valentines day card. Go big or go home, he though, and after a few days he had a talking Valentines day card that would become one of his wife’s most treasured possessions.

The early 90s were a different time; in case you haven’t yet been made to feel very old yet today, 1991 is closer to 1970 than 2013 is to 1991. Likewise, the circuitry inside this heartfelt talking token of appreciation bears more resemblance to something from a 1970s electronics magazine than an Arduino project of today.

The project is powered by an old Intel MCS-48 microcontroller attached to one of the old speech synthesis chips Radio Shack used to sell. These are, in turn, connected to a programmable logic chip and a masked ROM that translates English words into phonemes for the speech synthesizer.

The entire device is constructed on a hacked up piece of perf board and a few wire wrap sockets; sturdy construction, even if the battery compartment has been replaced a few times.

As for what the talking valentine says? “”OK!  Hello, I am a Talking Valentine Card.  “Love Is A Many-Splendored Thing” and in this case also needs batteries!” You can check that out after the break.

# Old School LED Light Show

Building LED arrays that can display all sorts of different patterns is pretty easy these days. Hook up an Arduino, do some charlieplexing, and off you go. When [Viktor] was younger he didn’t have all those fancy schmancy microcontrollers and circuit simulation software you kids have these days. In fact, last we heard, he had to walk to school uphill both ways – in the snow.

That didn’t stop him from building this gem of a project back in 1987. His LED chaser/light show does not use any microcontrollers at all, rather it relies on an EPROM to store predefined display programs. A series of switches are installed on the front of the flasher, allowing him to easily switch between the programs, and a pot is mounted to the front of the device to control the speed of the LEDs.

His light show is pretty slick, even for a project built over 20 years ago. Sometimes you just can’t beat a good, old-school hack.

Continue reading for a video demonstration of [Viktor’s] programmable light show.

# ITalkman Refrigerated Franken-phone

[Jani] over at MetkuMods was commissioned to build a prize for an on-air contest held by MTV3 in Finland. Well known for some of his previous work, he was a natural choice for this project. The only stipulation for the build was that it contain three specific items: a Mobira mobile phone, an Apple iPhone, and a refrigerator. For those of you who don’t know, a Mobira Talkman is an old-school “mobile” phone built by Nokia in the 80’s that weighed in at 11 pounds, and was far from convenient to use. In this case however, the size of the phone is an advantage since he was able to gut it and use the frame to make up the body of the refrigerated compartment. He sacrificed a soft-side portable heater/cooler bag, removing the built-in peltier cooler and associated components, later grafting them onto his Talkman case.

The next task was to add the iPhone to the Talkman. Rather than have the old handset sit there uselessly, [Jani] decided to mount a small Bluetooth hands-free module inside the handset, allowing it to answer calls, adjust the volume, and change music tracks on the iPhone. The iPhone was put in a hard plastic case, then mounted to the Talkman handset where the keypad and display used to reside.

All in all, the iTalkman is a pretty cool looking device, though we wouldn’t want to be tasked with lugging that thing around all day!