[Ken Shirriff] Demystifies BeagleBone I/O

If you have ever spent a while delving into the bare metal of talking to the I/O pins on a contemporary microprocessor or microcontroller you will know that it is not always an exercise for the faint-hearted. A host of different functions can be multiplexed behind a physical pin, and once you are looking at the hardware through the cloak of an operating system your careful timing can be derailed in an instant. For these reasons most of us will take advantage of other people’s work and use the abstraction provided by a library or a virtual filesystem path.

If you have ever been curious enough to peer under the hood of your board’s I/O then you may find [Ken Shirriff]’s latest blog post in which he explores the software stack behind the pins on a BeagleBone Black to be of interest. Though its specifics are those of one device, the points it makes have relevance to many other similar boards.

He first takes a look at the simplest way to access a Beagle Bone’s I/O lines, through virtual filesystem paths. He then explains why relying so heavily on the operating system in this way causes significant timing issues, and goes on to explore the physical registers that lie behind the pins. He then discusses the multiplexing of different pin functions before explaining the role of the Linux device tree in keeping operating system in touch with hardware.

For some Hackaday readers this will all be old news, but it’s safe to say that many users of boards like the BeagleBone Black will never have taken a look beyond the safely abstracted ways to use the I/O pins. This piece should therefore provide an interesting education to the chip-hardware novice, and should probably still contain a few nuggets for more advanced users.

We’ve seen a lot of [Ken]’s work here at Hackaday over the years, mostly in the field of reverse engineering. A few picks are his explanation of the TL431 voltage reference, a complete examination of the 741 op-amp, and his reverse engineering of the 1970s Sinclair Scientific calculator.

We appreciate [Fustini]’s tip on this story.

BeagleBone Black image: BeagleBoard.org Foundation [CC BY-SA 3.0], via Wikimedia Commons.

Introducing The Teensy 3.5 And 3.6

Paul Stoffregen has built a new Teensy. The latest in the line of very powerful, USB-capable microcontrollers is the Teensy 3.5 and 3.6 development boards. It’s faster, more capable, and bigger putting even more pins on a solderless breadboard.

The first Teensy was one of the first Arduino compatible boards with native USB. The Teensy 2.0 was even better with support for USB keyboards, mice, and MIDI. Even today, the Teensy 2.0 is the de facto board to use if you want to build anything like a USB keyboard. The Teensy 2.0 was followed by the exceptionally powerful Teensy 3.0, the first 32-bit Arduino compatible board, and thanks to Paul’s contributions of a pile of Arduino libraries, doing cool stuff faster has never been easier. Since the launch of the Teensy 3.0, its successors, the 3.1 and 3.2 have launched. If you want the power of an ARM microcontroller with the deepest Arduino library support, there’s only one board you should consider.

Like the launch of the Teensy 3.0, Paul is Kickstarting the launch of the latest Teensys with a crowdfunding campaign. Let’s dig into everything these new boards have to offer.

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Etching a PCB In Ten Minutes.

Most circuit boards any maker could need for their projects can be acquired online at modest cost, but what if you need something specific? [Giorgos Lazaridis] of pcbheaven.com has designed his own etching bath complete with a heater and agitator to sped up the process of creating your own custom circuit boards.

[Lazaridis] started by building a circuit to control — in a display of resourcefulness — a fish tank heater he would later modify. The circuit uses a PIC 16F526 microcontroller and two thermristors to keep the temperature of the etching bath between 38 and 41 degrees Celsius. The fish tank heater was gingerly pried from its glass housing, and its bimetallic strip thermostat removed and replaced with a wire to prevent it shutting off at its default 32 degrees. All of it is mounted on a small portable stand and once heated up, can etch a board in less than 10 minutes.

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Bluetooth HID Gamepad And HC-05 Serial Hack

“Which came first, the chicken or the egg?” Don’t bother us with stupid questions, they both co-evolved into the forms that we now serve up in tasty sandwiches or omelets, respectively. “Which came first, the HC-05 serial-flash-hack, or the wireless Bluetooth Gamepad?” Our guess is that [mitxela] wanted to play around with the dirt-cheap Bluetooth modules, and that building the wireless controller was an afterthought. But for that, it’s a well-done afterthought! (Video below the break.)

It all starts with the HC-05 Bluetooth module, which is meant to transfer serial data, but which can be converted into a general-purpose device costing ten times as much with a simple Flash ROM replacement. The usual way around this requires bit-banging over a parallel port, but hackers have worked out a way to do the same thing in bit-bang mode using a normal USB/Serial adapter. The first part of [mitxela]’s post describes this odyssey.

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Electroshock Timer Will Speed Up Every Game of Settlers of Catan

The fun of playing Settlers of Catan is only matched by the desire to punch your friend when their turn drags on with endless deliberating. [Alpha Phoenix] has solved that quandary of inefficient play by building the Settlers of Catan: Electroshock Therapy Expansion.

[Alpha Phoenix] is holding back on the details of the device to forestall someone trying this at home and injuring themselves or others, but there’s plenty to glean from his breakdown of how the device works. An Adafruit Trinket microcontroller connects to a single pole 12 throw switch — modified from a double pole six throw rotary switch — to select up to six different players (with the other six positions alternated in as pause spaces) and the shocks are delivered through a simple electrode made from a wire hot glued to HDPE plastic from a milk jug. The power supply is capable of delivering up to 1100V, but the actual output is much less than that, thanks to its built-in impedance of about 2.5M Ohms, as well as added resistance by [Alpha Phoenix].

To define what constitutes a ‘long turn,’ the Trinket calculates the mean of up to the first 100 turn lengths (instead of a static timer to accommodate for the relative skills of the players in each game) and zaps any offending player — and then repeatedly at a set time afterwards — to remind them that they need to pick up the pace.

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Two Pins for the Price of One

One of the most common problems in the world of microcontrollers is running out of resources. Sometimes it’s memory, where the code must be pared down to fit into the flash on the microcontroller. Other times, as [Fabien] found out when he ran out of pins, the limitations are entirely physical. Not one to give up, he managed to solve the problem by using one pin for two tasks. (Google Translate from French)
During a recent project, [Fabien] realized he had forgotten to add a piezo buzzer to his project. All of the other pins were in use, though, so his goal was to use one of the input pins to handle button presses but to occasionally switch to output mode when the piezo buzzer was needed. After all, the button is only used at certain times, and the microcontroller pin sits unused otherwise. After a few trials, he has a working solution that manages to neither burn out itself nor the components in the circuit, and none of the components interfere with the other’s normal operation.
While it isn’t the most technically advanced thing we’ve ever seen here, it is a great example of using the tools at your disposal to elegantly solve a problem. More than that, though, it’s a thorough look into the details of pull-up and pull-down resistors, how microcontrollers see voltage as logic levels, and how other pieces of hardware interact with microcontrollers of all different types. This is definitely worth a read, especially if you are a beginner in this world.

Jump In When The Water Is Just Right With A Wireless Swimming Pool Thermometer

[David]’s family acquired a swimming pool. While it’s not his favorite activity in the world, every now and then he’ll indulge in the blue plastic bin full of water occupying previously pristine land in his backyard.

As he says, cool beer is pleasant, but cool water tends to put a damper on the experience. Rather than do something pedestrian like touch the water himself to discover its temperature; he saw an opportunity for a fun little project in a wireless temperature monitor.

The heart of the device is a Telecom Design TD1208 which runs on the French SigFox network. For a small fee any device on the network can send up to 140 12byte packets of data a day. Not a lot, but certainly acceptable for the Microchip MCP9700 temperature sensor it uses. He got the board up and running, and even made his own custom helical coil antenna.

The case was 3D printed out of PLA. It’s a tiered cylindrical bobber. The wider top section floats on the water and the base acts as a ballast, holding the battery and sensor.  The bobber is powered by a combination of  a questionable Chinese lithium battery, charging circuit, and solar panel. [Dave] was keen to point out that the battery is, technically, water cooled.

He wrapped up the code for the bobber and used SigFox’s SDK to build a nice web interface. Now, when the rare mood strikes him, he can remain inside if the conditions aren’t right for a swim.