# Arduino + Geometry + Bicycle = Speedometer

It is pretty easy to go to a big box store and get a digital speedometer for your bike. Not only is that no fun, but the little digital display isn’t going to win you any hacker cred. [AlexGyver] has the answer. Using an Arduino and a servo he built a classic needle speedometer for his bike. It also has a digital display and uses a hall effect sensor to pick up the wheel speed. You can see a video of the project below.

[Alex] talks about the geometry involved, in case your high school math is well into your rear view mirror. The circumference of the wheel is the distance you’ll travel in one revolution. If you know the distance and you know the time, you know the speed and the rest is just conversions to get a numerical speed into an angle on the servo motor. The code is out on GitHub.

# Newton’s Cradle for Those Too Lazy to Procrastinate

Desk toys are perfect for when you don’t want to work. There’s a particularly old desk toy called the Newton’s cradle. If you don’t know the name, you’d still recognize the toy. It is some ball bearings suspended in midair on strings. If you pull back, say, two balls and let them swing to impact the other balls, the same number of balls on the other side will fly out. When they return, the same number will move on the other side and this repeats until friction wears it all down.

We think [JimRD] might be carried away on procrastination. You see, he not only has a Newton’s cradle, he has automated it with an Arduino. According to [Jim], this is his third attempt at doing so. You can see the current incarnation in the video, below.

# Modified Servo Adds Focus Control to Telescope

Scanning the heavens with a telescope is a great way to spend long, clear winter nights, but using a manual telescope can get to be a drag. A motorized mount with altitude and azimuth control is basic equipment for the serious observer, but adding a servo to control the focus of your telescope is one step beyond your average off-the-shelf instrument.

Having already motorized the two axes of the equatorial mount of his modest telescope as a senior project, [Eric Seifert] decided to motorize the focus rack as well. His first inclination was to use a stepper motor like he did on the other two axes, but with a spare high-torque servo at hand, he hacked a quick proof-of-concept. The servo was modified for continuous rotation in the usual way, but with the added twist of replacing the internal potentiometer with an external linear pot. Attached to the focus tube, the linear pot allows [Eric] to control the position and speed of the modified servo. Sounds like controlling the focus will be important to [Eric]’s planned web interface for his scope; we’ll be looking for details on that project soon.

We like the simplicity of this solution, and it’s a trick worth keeping in mind for other projects.  But if fancy steppers and servos aren’t your thing, fear not — astrophotography is as easy as slapping a couple of boards together with a hinge.

# Raspberry Pi and Alexa Make Teddy Ruxpin Smarter than the Average Bear

Behold the unholy union of Amazon’s Alexa and that feature-limited animatronic bear from the 80s, Teddy Ruxpin. Alexa Ruxpin?

As if stuffing Alexa inside a talking fish weren’t bad enough, now Amazon’s virtual assistant can talk to you through the creepy retro plush thanks to [Tinkernut]’s trip down memory lane. Having located a Teddy Ruxpin on eBay for far less than the original \$70 that priced it out from under his childhood Christmas tree, [Tinkernut] quickly learned that major surgery would be necessary to revive the Ruxpin. The first video below shows the original servos being gutted and modern micro servos grafted in, allowing control of the mouth, eyes, and nose via an Arduino.

With the bear once again in control of its faculties, [Tinkernut] embarked on giving it something to talk about. A Raspberry Pi running AlexaPi joined the bear’s recently vacated thorax with the audio output split between the bear’s speaker and the analog input on the Arduino. The result is a reasonable animation, although we’d say a little tweaking of the Arduino script might help the syncing. And those eyes and that nose really need to get into the game as well. But not a bad start at all.

This isn’t the first time that Teddy Ruxpin has gone under the knife in the name of hacks, and it likely won’t be the last. And the way toy manufacturers are going, they might just beat us hackers to the punch.

# Real-Time Planet Tracker With Laser-Point Accuracy

Space. The final frontier. Unfortunately, the vast majority of us are planet-locked until further notice. If you are dedicated hobbyist astronomer, you probably already have the rough positions of the planets memorized. But what if you want to know them exactly from the comfort of your room and educate yourself at the same time? [Shubham Paul] has gone the extra parsec to build a Real-Time Planet Tracker that calculates their locations using Kepler’s Laws with exacting precision.

An Arduino Mega provides the brains, while 3.5-turn-pan and 180-degree-tilt servos are the brawn. A potentiometer and switch allow for for planet and mode selection, while a GPS module and an optional MPU9250 gyroscope/magnetometer let it know where you are. Finally a laser pointer shows the planet’s location in a closed room. And then there’s code: a lot of code.

The hardware side of things — as [Shubham Paul] clarifies — looks a little unfinished because the focus of the project is the software with the intent to instruct. They have included all the code they wrote for the RTPT, providing a breakdown in each section for those who are looking to build their own.

# DIY Mini Printer is 95% Wood, Prints Tiny Cute Images

This little DIY 64×64 graphical printer by [Egor] is part pen plotter in design, somewhat dot matrix-ish in operation, and cleverly designed to use unmodified 9G servos. The project page is all in Russian (translation to English here) but has plenty of photos that make the operation and design clear. Although nearly the entire thing is made from laser-cut wood, [Egor] says that a laser cutter is optional equipment. The first version was entirely cut with hand tools.

Small DIY CNC machines driven over a serial line commonly use Arduinos and CD-ROM drive guts (like this Foam Cutter or this Laser Paper Cutter) but this build uses its own custom rack-and-pinion system, and has some great little added details like the spring-loaded clip to hold paper onto the print pad.

The frame and parts (including all gears) are laser-cut from 4 mm plywood and the unit is driven by three small servos. A simple Java program processes images and an Arduino UNO handles the low-level control. A video of everything in action is embedded below.
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# Blynk with Joy

Last time, I talked about how my storage situation and my cheap nature led me to build an RC joystick controller with a cell phone app and an ESP8266. The key to making this easy was to use the GUI builder called Blynk to make a user interface for an Android or Apple phone. Blynk can communicate with the ESP8266 and makes the project relatively simple.

## ESP8266 and Arduino IDE

The ESP8266 Blynk code is straightforward. You do need to set up the Arduino IDE to build for the ESP8266. That can vary by board, but here’s the instructions for the board I was using (from Adafruit; see below).

Depending on the type of ESP8266 device you are using, you may need a 3.3 V serial cable or some other means of getting the firmware into the device. For the Adafruit device I had, it has a 5 V-tolerant serial connection so a standard USB to serial dongle plugs right in. There’s also two switches on my device. To get into bootload mode, you have to push the one button down, hold it, and then press the reset button. Once you release the reset button you can release the other button. The red LED half-glows and the device is then waiting for a download.
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