Fail Of The Week: Don’t Tie Those Serial Lines High

Fail Of The Week is a long-running series here at Hackaday. Over the years we’ve been treated to a succession of entertaining, edifying, and sometimes downright sad cock-ups from many corners of the technological and maker world.

You might think that we Hackaday writers merely document the Fails of others, laughing at others’ misfortunes like that annoying kid at school. But no, we’re just as prone to failure as anyone else, and it is only fair that we eat our own dog food and tell the world about our ignominious disasters when they happen.

And so we come to my week. I had a test process to automate for my contract customer. A few outputs to drive some relays, a few inputs from buttons and microswitches. Reach for an Arduino Uno and a prototyping shield, divide the 14 digital I/O lines on the right into 7 outputs and 7 inputs. Route 7 to 13 into a ULN2003 to drive my relays, tie 0 to 6 high with a SIL resistor pack so I can trigger them with switches to ground. Job done, and indeed this is substantially the hardware the test rig ended up using.

So off to the Arduino IDE to write my sketch. No rocket science involved, a fairly simple set of inputs, outputs, and timers. Upload it to the Arduino, and the LED on pin 13 flashes as expected. Go for a well-deserved lunch as a successful and competent engineer who can whip up a test rig in no time.

Back at the bench refreshed by the finest British pub grub, I started up the PC, plugged the shield into the Arduino, and applied the power. My sketch worked. But wait! There’s a slight bug! Back to the IDE, change a line or two and upload the sketch.

And here comes my fail. The sketch wouldn’t upload, the IDE reported a COM port error. “Damn’ Windows 10 handling of USB serial ports”, I thought, as I’m not a habitual Windows user on my own machines. Then followed something I’ve not done for quite a while; diving into the Windows control panel to chase the problem. Because it had to be a Windows problem, right?

arduino-serial-pinsThe seasoned Arduinisti among you probably spotted my fail four paragraphs ago. We all know that pins 0 and 1 on an Arduino are shared with the serial port, but who gives it a second thought? I guess I’d always had the good fortune to drive those pins from lines which didn’t enforce a logic state, and had never ended up tying them high. Hold them to a logic 1, and the Arduino can’t do its serial thing so sketches stay firmly in the IDE.

I could have popped the shield off every time I wanted to upload a new sketch, but since in the event I didn’t need all those inputs I just lifted the links tying those pins high and shifted the other inputs up the line. And went home that evening a slightly less competent engineer whose ability to whip up a test rig in no time was a bit tarnished. Ho hum, at least the revised sketch worked and the test rig did its job exactly as it should.

So that’s my Fail Of The Week. What’s yours?

Header image:, CC-BY-ND via MarkusJenkins

2013-09-05-Hackaday-Fail-tips-tileFail of the Week is a Hackaday column which celebrates failure as a learning tool. Help keep the fun rolling by writing about your own failures and sending us a link to the story — or sending in links to fail write ups you find in your Internet travels.

Small Experiments in DIY Home Security

[Dann Albright] writes about some small experiments he’s done in home security.

He starts with the simplest. Which is to purchase an off the shelf web camera, and hook it up to software built to do the task. The first software he uses is the free, iSpy open source software. This adds basic features like motion detection, time stamping, logging, and an interface. He also explores other commercial options.

Next he delves a bit deeper. He starts by making a simple motion detector. When the Arduino detects motion using a PIR sensor it gets a computer to text an alert. After the tutorial begins to veer a little and he adds his WiFi light bulbs to the mix. Now he can send an email and change the color of the lights.

We suppose, that from a security standpoint. It would really freak a burglar out if all the lights turned red when they walked into a room. Either way, there’s definitely a fun weekend project in playing around with all these systems.

Gear Clock Uses Stepper Motor

[Rjeuch] liked a wooden clock he saw on the Internet, but the gears were produced with a proprietary software tool. So he built his own version. Unlike the original, however, he chose to use a stepper motor to drive the hands.

The clock’s gears aren’t just for show, and the post does a good job explaining how the gears work, how you might customize them, and how they fit together. The clock’s electronics rely on an Arduino.

Continue reading “Gear Clock Uses Stepper Motor”

Home Made Pen Plotter

As someone who started using computers in the last century, I find the current resurgence of pen plotters somewhat nostalgic. The difference, of course, is that this century it is easier to make your own, which is what [Miguel Sanchez] is doing.

Inspired by the Axidraw, he is making his own pen plotter. He’s made great progress so far, creating a design that looks quite simple to build. His design is driven by an Arduino Uno with a stepper shield, a couple of NEMA 17 stepper motors and a servo to raise and lower the pen. Throw in a few rods, a belt or two and a number of 3D printed parts, and you’ve got a decent looking pen plotter.

He originally started with laser cut components, but shifted over to 3D printing as the design evolved. It’s not as fancy as the HP pen plotter I used to print out rude words in giant letters with in my youth (a HP7475, I think), but it is a neat build. Check it in action in the video below.

Continue reading “Home Made Pen Plotter”

Arduino Quadcopter Game Uses Serial Monitor

Every new generation of computers repeats the techniques used by the earlier generations. [Kim Salmi] created an ASCII-based quadcopter simulation game using an Arduino that displays on the Arduino serial monitor. The modern twist is the controller: an accelerometer supplements the joystick for immersive play. And of course there are flashing LEDs.

An Arduino Uno provides the processing power and drives the serial monitor. A joystick and a Hitachi H48C accelerometer are mounted on a breadboard and wired to the Uno. The tilting of the accelerometer controls the height and left-right motion of the quadcopter on the screen. The joystick sets the the ‘copter in hover mode and lowers a ‘rescue’ line. Another LED warns when the maximum height, the vertical limit of the screen, is reached. The joystick also selects one of the three quadcopters, which have different performance characteristics.

There’s a video after the break. [Kim] provides the source code so  you use it as a reference for handling the joystick and accelerometer inputs.

More proof that what is old is new.  Continue reading “Arduino Quadcopter Game Uses Serial Monitor”

Atomic Arduino (and Other) Development

Even the most die-hard Arduino fan boys have to admit that the Arduino development environment isn’t the world’s greatest text editor (they’d probably argue that its simplicity is its strength, but let’s ignore that for now). If you are used to using a real code editor, you’ll probably switch to doing your Arduino coding in that and then use the external editor integration in the IDE.

That works pretty well, but there are other options. One we noticed, PlatformIO, extends GitHub’s Atom editor. That makes it cross-platform, powerful, and with plenty of custom plug ins. It also supports a range of platforms including Arduino, many ARM platforms, MSP430, and even desktop computers running Linux or Windows.

Continue reading “Atomic Arduino (and Other) Development”


Servos are extremely versatile actuators used in a large number of applications which need controlled mechanical movement. The usual way of driving them is by using a PWM output from a micro-controller. But if you’re building a robot or a drone which requires a large number of servos, then it makes sense to add smarts directly to the servo.

[Alvaro Ferrán Cifuentes] did just that by building IntelliServo – an add on board which makes regular servos smart by giving them enhanced capabilities as found in high-end versions. His approach is different compared to other takes on this theme. The IntelliServo is designed to replace the electronics in any regular servo and is not limited to any particular make or type. Once upgraded, it’s possible to read the servos position, temperature and current consumption. This allows interesting uses, such as controlling one servo by moving another one, or detecting collision or stalling by monitoring the servo current. Multiple servos can be daisy-chained and controlled over I²C from a micro-controller, or over USB directly from a computer. Each board features an LPC11U24 32-bit Cortex-M0 micro-controller, a DRV8837 motor driver, a TMP36 temperature sensor and a PCA9508 I²C repeater.

The project is open source and the Github repository contains the board design, Arduino library and examples, servo firmware and mechanical parts as well as use instructions. It’s a modular design which allows using either an external controller or running it directly via the on-board micro-USB socket. Check out the videos after the break to see the IntelliServo in action.

Continue reading “IntelliServo”