Execution Tracing On Cortex-M3 Microcontrollers

March 9, 2015 by Brian Benchoff 14 Comments

The higher-power ARM micros have a bunch of debugging tools for program and data tracing, as you would expect. This feature – CoreSight Trace Macrocells – is also found in the lowly ARM Cortex M3 microcontroller. The Cortex M3 is finding its way into a lot of projects, and [Petteri] wondered why these debugging tools weren’t seen often enough. Was it a question of a lack of tools, or a lack of documentation? It doesn’t really matter now, as he figured out how to do it with a cheap logic analyzer and some decoders for the trace signals.

There are two trace blocks in most of the Cortex M3 chips: the ITM and ETM. The Instrumentation Trace Macrocell is the higher level of the two, tracing watchpoints, and interrupts. The Embedded Trace Macrocell shows every single instruction executed in the CPU. Both of these can be read with a cheap FX2-based logic analyzer that can be found through the usual outlets for about $10. The problem then becomes software, for which [Petteri] wrote a few decoders.

To demonstrate the debugging capability, [Petteri] tracked down a bug in his CNC controller of choice, the Smoothieboard. Every once in a great while, the machine would miss a step. With the help of the trace tool and by underclocking the micro, [Petteri] found the bug in the form of a rounding error of the extruder. Now that he knows what the bug is, he can figure out a way to fix it. He hasn’t figured that out yet. Still, knowing what to fix is invaluable and something that couldn’t be found with the normal set of tools.

Logic Noise: Sawing Away With Analog Waveforms

March 9, 2015 by Elliot Williams 14 Comments

Today we’ll take a journey into less noisy noise, and leave behind the comfortable digital world that we’ve been living in. The payoff? Smoother sounds, because today we start our trip into analog.

If you remember back to our first session when I was explaining how the basic oscillator loads and unloads a capacitor, triggering the output high or low when it crosses two different thresholds. At the time, we pointed out that there was a triangle waveform being generated, but that you’d have a hard time amplifying it without buffering. Today we buffer, and get that triangle wave out to our amplifiers.

But as long as we’re amplifying, we might as well overdrive the amps and head off to the land of distortion. We’ll do just that and build up a triangle-wave oscillator that can morph into a square wave, passing through a rounded-over kinda square wave along the way. The triangle sounds nice and mellow, and the square wave sounds bright and noisy. (You should be used to them by now…) And we get everything in between.

And while we’re at it, we might as well turn the triangle wave into a sawtooth for that nice buzzy-bass sound. Then we can turn the fat sawtooth into a much brighter sounding pulse wave, a near cousin of the square wave above.

What’s making all this work for us? Some dead-boring amplification with negative feedback, and the (mis-)use of a logic chip to get it. After the break I’ll introduce our Chip of the Day: the 4069UB.

If you somehow missed them, here are the first three installments of Logic Noise:

Continue reading “Logic Noise: Sawing Away With Analog Waveforms” →

Ask Hackaday: The Many Uses Of Microwaves

March 9, 2015 by Will Sweatman 73 Comments

When most think of a microwave, they think of that little magic box that you can heat food in really fast. An entire industry of frozen foods has sprung up from the invention of the household microwave oven, and it would be difficult to find a household without one. You might be surprised that microwave ovens, or reactors to be more accurate, can also be found in chemistry labs and industrial complexes throughout the world. They are used in organic synthesis – many equipped with devices to monitor the pressure and temperature while heating. Most people probably don’t know that most food production facilities use microwave-based moisture solids analyzers. And there’s even an industry that uses microwaves with acids to dissolve or digest samples quickly. In this article, we’re going to look beyond the typical magnetron / HV power supply / electronics and instead focus on some other peculiarities of microwave reactors than you might not know.

Single vs Multimode

The typical microwave oven in the millions of households across the world is known as multimode type. In these, the microwaves will take on typical wavelike behavior like we learned about in physics 101. They will develop constructive and destructive interference patterns, causing ‘hot spots’ in the cavity. A reader tipped us off to this example, where [Lenore] uses a popular Indian snack food to observe radiation distribution in a multimode microwave cavity. Because of this, you need some type of turntable to move the food around the cavity to help even out the cooking. You can avoid the use of a turn table with what is known as a mode stirrer. This is basically a metal ‘fan’ that helps to spread the microwaves throughout the cavity. They can often be found in industrial microwaves. Next time you’re in the 7-11, take a look in the top of the cavity, and you will likely see one.

Multimode microwaves also require an isolator to protect the magnetron from reflected energy. These work like a diode, and do not let any microwaves bounce back and hit the magnetron. It absorbs the reflected energy and turns it into heat. It’s important to note that all microwave energy must be absorbed in a multimode cavity. What is not absorbed by the food will be absorbed by the isolator. Eventually, all isolators will fail from the heat stress. Think about that next time you’re nuking a small amount of food with a thousand watts!

Single Mode microwaves are what you will find in chemistry and research labs. In these, the cavity is tuned to the frequency of the magnetron – 2.45GHz. This allows for a uniform microwave field. There is no interference, and therefore no hot or cold spots. The microwave field is completely homogenous. Because of this, there is no reflected energy, and no need for an isolator. These traits allow single mode microwaves to be much smaller than multimode, and usually of a much lower power as there is a 100% transfer of energy into the sample. While most multimode microwaves are 1000+ watts, the typical single mode will be around 300 watts.

Power Measurement

Most microwave ovens only produce one power level. Power is measured and delivered by the amount of time the magnetron stays on. So if you were running something at 50% power for 1 minute, the magnetron would be on for a total of 30 seconds. You can measure the output power of any microwave by heating 1 liter of water at 100% power for 2 minutes. Multiply the difference in temperature by 35, and that is your power in watts.

There are other types of microwaves that control power by adjusting the current through the magnetron. This type of control is often utilized by moisture solids analyzers, where are more precise control is needed to keep samples from burning.

Have you used a microwave ~~and an arduino~~ for something other than cooking food? Let us know in the comments!

Thanks to [konnigito] for the tip!

Convert A Rotary Phone To VOIP Using Raspberry Pi

March 9, 2015 by Theodora Fabio 19 Comments

There’s something so nostalgic about the rotary phone that makes it a fun thing to hack and modernize. [Voidon] put his skills to the test and converted one to VoIP using a Raspberry Pi. He used the RasPi’s GPIO pins to read pulses from the rotary dial – a functional dial is always a welcome feature in rotary phone hacks. An old USB sound card was perfect for the microphone and handset audio.

As with any build, there were unexpected size issues that needed to be worked around. While the RasPi fit inside the case well, there was no room for the USB power jack or an ethernet cable, let alone a USB power bank for portability. The power bank idea was scrapped. [voidon] soldered the power cord to the RasPi before the polyfuse to preserve the surge protection, used a mini-USB wifi dongle, and soldered a new USB connector to the sound card. [Voidon] also couldn’t get the phone’s original ringer to work, so he used the Raspberry Pi’s internal sound card to play ringtones.

The VoIP (SIP) was managed by some Python scripting, available at GitHub. [voidon] has some experience in using Asterisk at his day job, so it will be interesting to see if he incorporates it in the future.

[via Reddit]

Glowing LED Cubes From The Future

March 9, 2015 by Rich Bremer 28 Comments

Sometimes people don’t believe you when you tell them something. You may have to go out of your way to convince those skeptics. Well, [AlexTheGreat] was having a hard time convincing people that he was from the future. He thought building some cool looking glowing LED cubes would help his story.

Underneath the fancy exterior covering is a cube made from pieces of clear acrylic sheet that are hot-glued together. There isn’t much inside the cube, just an LED, resistor, button cell battery and an on/off switch. A hole in one of the cube sides allows access to the on/off switch. Once all the components are verified to work, the interior of the cube is filled with hot glue to diffuse the light.

The exterior is thin sheet metal cut into cool shapes and bent around the plastic cube. Like the rest of the components, these metal covers are held on with hot glue. They do a great job of blocking the LED light ensuring it shines out of the creatively arranged gaps. We’re not sure if these will convince anyone that [AlexTheGreat] is from the future but they are certainly darn cool looking!

USB Powered CD Lamp

March 8, 2015 by Rich Bremer 13 Comments

[Artificial Intelligence] has made a desk lamp out of parts he had kicking around in his parts bin. Most recognizable are the 4 CDs that make up the base and the shade. To start this project, [Artificial Intelligence] sketched out a circular pattern on one of the CDs and marked 7 locations where the LEDs will be. Holes were drilled at those marked locations, the LEDs inserted and hot glued into place. Each LED has its own current limiting resistor soldered in a series configuration.

[Artificial Intelligence] mentions the resistor value was determined by a nice LED resistor calculator he found online, ledcalc.com. Then each LED/resistor combo was wired together in a parallel configuration and covered up by another CD to clean up the look and protect the wiring.

The base, like the top, is also made from 2 CDs, but this time there are 5 AA batteries underneath the CDs. These batteries don’t power the lamp, they are only used as a counterweight to prevent the lamp from tipping over. A USB cord runs to the lamp base, goes through an on/off switch and then up a pair of large-gauge solid core wire before connecting to the LED’s in the top of the lamp. The thick solid core wire acts as the only support for the lamp shade and LEDs. Since it is still just wire, the lamp can be bent to shine light in the most convenient position, as any good desk lamp would be capable of.

Combination Lock Made Out Of Paper

March 8, 2015 by Bryan Cockfield 9 Comments

Most projects we feature are of the metal/wire/wood variety, but there is an entire community devoting to making very interesting and intricate things out of paper. Imgur user [Criand] has been hard at work on his own project made entirely out of paper, a combination lock that can hold a secret message (reddit post).

The motivation for the project was as a present for a significant other, wherein a message is hidden within a cryptex-like device and secured with a combination that is of significance to both of them. This is similar to how a combination bike lock works as well, where a series of tumblers lines up to allow a notched shaft to pass through. The only difference here is that the tiny parts that make up the lock are made out of paper instead of steel.

This project could also be used to gain a greater understanding of lock design and locksport, if you’ve ever been curious as to how this particular type of lock works, although this particular one could easily be defeated by a pair of scissors (but it could easily cover rock). If papercraft is more of your style though, we’ve also seen entire gyroscopes and strandbeests made of paper!