ARM Board Transmits FM

There is more than a casual link between computer people and musicians. Computers have created music since 1961 when an IBM7094 sang the song Daisy Bell (later inspiring another computer, the HAL 9000, to do the same).

[Vinod.S] wanted to create music on an STM32F407 Discovery board, but he also wanted it to play on his FM radio. He did it, and his technique was surprising and straightforward. The key is that the ARM processor on the Discovery board uses an 8MHz crystal, but internally (using a phase-locked loop, or PLL) it produces a 100MHz system clock. This happens to be right in the middle of the FM radio band. Bringing that signal back out of the chip on a spare output pin gives you the FM carrier.

That’s simple, but a carrier all by itself isn’t sufficient. You need to FM modulate the carrier. [Vinod.S] did the music playback in the usual way and fed the analog signal via a resistor to the crystal. With some experimentation, he found a value that would pull the crystal frequency enough that when multiplied up to 100MHz, it would produce the desired amount of FM deviation. You can see a video of the whole thing in action, below.

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The Internet of Linux Things

The Linux Foundation is a non-profit organization that sponsors the work of Linus Torvalds. Supporting companies include HP, IBM, Intel, and a host of other large corporations. The foundation hosts several Linux-related projects. This month they announced Zephyr, an RTOS aimed at the Internet of Things.

The project stresses modularity, security, and the smallest possible footprint. Initial support includes:

  • Arduino 101
  • Arduino Due
  • Intel Galileo Gen 2
  • NXP FRDM-K64F Freedom

The project (hosted on its own Website) has downloads for the kernel and documentation. Unlike a “normal” Linux kernel, Zephyr builds the kernel with your code to create a monolithic image that runs in a single shared address space. The build system allows you to select what features you want and exclude those you don’t. You can also customize resource utilization of what you do include, and you define resources at compile time.

By default, there is minimal run-time error checking to keep the executable lean. However, there is an optional error-checking infrastructure you can include for debugging.

The API contains the things you expect from an RTOS like fibers (lightweight non-preemptive threads), tasks (preemptively scheduled), semaphores, mutexes, and plenty of messaging primitives. Also, there are common I/O calls for PWM, UARTs, general I/O, and more. The API is consistent across all platforms.

You can find out more about Zephyr in the video below. We’ve seen RTOS systems before, of course. There’s even some for robots. However, having a Linux-heritage RTOS that can target small boards like an Arduino Due and a Freedom board could be a real game changer for sophisticated projects that need an RTOS.

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When Are 8 Bits More Than 32?

Whenever we write up a feature on a microcontroller or microcontroller project here on Hackaday, we inevitably get two diametrically opposed opinions in the comments. If the article featured an 8-bit microcontroller, an army of ARMies post that they would do it better, faster, stronger, and using less power on a 32-bit platform. They’re usually right. On the other hand, if the article involved a 32-bit processor or a single-board computer, the 8-bitters come out of the woodwork telling you that they could get the job done with an overclocked ATtiny85 running cycle-counted assembly. And some of you probably can. (We love you all!)

redblue_pillWhen beginners walk into this briar-patch by asking where to get started, it can be a little bewildering. The Arduino recommendation is pretty easy to make, because there’s a tremendous amount of newbie-friendly material available. And Arduino doesn’t necessarily mean AVR, but when it does, that’s not a bad choice due to the relatively flexible current sourcing and sinking of the part. You’re not going to lose your job by recommending Arduino, and it’s pretty hard to get the smoke out of one.

But these days when someone new to microcontrollers asks what path they should take, I’ve started to answer back with a question: how interested are you in learning about microcontrollers themselves versus learning about making projects that happen to use them? It’s like “blue pill or red pill”: the answer to this question sets a path, and I wouldn’t recommend the same thing to people who answered differently.

For people who just want to get stuff done, a library of easy-to-use firmware and a bunch of examples to crib learn from are paramount. My guess is that people who answer “get stuff done” are the 90%. And for these folks, I wouldn’t hesitate at all to recommend an Arduino variant — because the community support is excellent, and someone has written an add-on library for nearly every gizmo you’d want to attach. This is well-trodden ground, and it’s very often plug-and-play.

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Tiny USB Morse Code Beacon

It is reasonably easy to make a microcontroller spit out some Morse code. What makes [pavlin’s] take on this project interesting is that it resides on a tiny USB board with an ARM processor. The design for the board is available with single-sided artwork suitable for production using simple methods like toner transfer.

The STM device has a built-in USB bootloader. It can also act as a serial port, which makes the project very simple. The only external parts are a speaker and an optoisolator. The program provides a command line interface over the serial port that you can use to program the message and set other options like speed and the delay between messages. The code is available on GitHub.

You might argue that a beacon shouldn’t need a USB port, and we’ve seen an alternative that fits the bill. If you want a much larger Arduino-based keyer, we’ve seen those, too.

Back to the Drawing Board

Ever try signing your name with a mouse or a trackball? Not so easy. You could buy a graphics tablet with a pen. [Rahul Ramakrishnan] has a different approach. He took two 10-turn pots, and attached some strings and a washer. A pencil goes through the washer, and a BeagleBone Black reads the pots to determine what it is drawing on the paper. A couple of retractable badge lanyards keep tension on the string.

This ingenious design would be easy enough to replicate with any microcontroller that can read the two pots. The only awkward part is the need to press a button down when you want the device to treat the pencil as down (see the video below). It would probably be easy to rig up some switch on the pencil to make operation a little smoother.

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Pi Zero Video Card Via Bare Metal Programming

Rolling your own synthesizer is no small feat, which is what [Thomas] has taken on with his project “Nerdsynth”. [Thomas] has an impressive amount of data on his site covering the overall design and progress of the project, but that isn’t what piqued our interest. [Thomas] has an on-board TFT display to navigate the versatile Nerdsynth’s menu nerdsynth-sketchbut he wanted to add video output to  do some video sequencing. After some investigation and poking around the available options he decided to tackle yet another sub-project (textbook scope-creep).

[Thomas] chose to do to some bare metal programming on the Pi Zero to use it as a video card for video output. By following a tutorial  from Valvers and modifying an SPI driver from Microelecroniki he was able to clone the video on an external monitor. This is a step in the right direction and we’ll have to keep an eye on his site for updates about video sequencing on the external display.

You can check out a recent demo of the Nerdsynth in action after the break, sadly you’ll have to settle for a pic of the cloned screen (below) until [Thomas] posts another update.


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PS/2 Keyboard for Raspberry Pi

A lot of people can bake a cake. Sort of. Most of us can bake a cake if we have a cake mix. Making a cake from scratch is a different proposition. Sure, you know it is possible, but in real life, most of us just get a box of cake mix. The Raspberry Pi isn’t a cake (or even a pie), but you could make the same observation about it. You know the Raspberry Pi is just an ARM computer, you could program it without running an available operating system, but realistically you won’t. This is what makes it fun to watch those that are taking on this challenge.

[Deater] is writing his own Pi operating system and he faced a daunting problem: keyboard input. Usually, you plug a USB keyboard into the Pi (or a hub connected to the Pi). But this only works because of the Linux USB stack and drivers exist. That’s a lot of code to get working just to get simple keyboard input working for testing and debugging. That’s why [Deater] created a PS/2 keyboard interface for the Pi.

Even if you aren’t writing your own OS, you might find it useful to use a PS/2 keyboard to free up a USB port, or maybe you want to connect that beautiful Model-M keyboard without a USB adapter. The PS/2 keyboard uses a relatively simple clock and data protocol that is well-understood. The only real issue is converting the 5V PS/2 signals to 3.3V for the Pi (and vice versa, of course).

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