Direct Digital Synthesis (DDS) Explained by [Bil Herd]

One of the acronyms you may hear thrown around is DDS which stands for Direct Digital Synthesis. DDS can be as simple as taking a digital value — a collection of ones and zeroes — and processing it through a Digital to Analog Converter (DAC) circuit. For example, if the digital source is the output of a counter that counts up to a maximum value and resets then the output of the DAC would be a ramp (analog signal) that increases in voltage until it resets back to its starting voltage.

This concept can be very useful for creating signals for use in a project or as a poor-man’s version of a signal or function generator. With this in mind I set out here to demonstrate some basic waveforms using programmable logic for flexibility, and a small collection of resistors to act as a cheap DAC. In the end I will also demonstrate an off-the-shelf and inexpensive DDS chip that can be used with any of the popular micro-controller boards available that support SPI serial communication.

All of the topics covered in the video are also discussed further after the break.

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How To Get 50 More Zed From Your Rigol DS1054Z

[Chris] has been spending a lot of time in the wife’s sewing room lately, and things got pretty serious late last night as he hacked his shiny new Rigol DS1054Z to unlock the 1104Z capabilities lurking within.

The rumors are true, and ungoverning the software is as simple as looking up your serial number and knowing the right URL for generating a valid license. [Chris] ran into a dud site, but that’s the price of doing business in the shadowy parking garage basements of the interwebs. Once he knocked on the right door and uttered the secret word, however, he became the proud owner of 50MHz additional bandwidth, decoders for SPI, I²C, and RS-232, twice the storage depth, and all teh triggers that ship with the 1104Z.

Stick around for [Chris]’s video walk-through. Can’t rationalize the purchase even at the ridiculously low price point? Here’s one way to make it happen. You’ll laugh, you’ll cry, you’ll learn some French.

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Which Way Are We Going? Concepts Behind Rotary Encoders

[Pete] needed a rotary encoder for one of his project so he set out to build his own. As the name implies, a rotary encoder measures rotation by encoding “steps” into electrical signals which can be measured by a microcontroller (or used in numerous other ways). Knowing the degrees of movement for each step will allow you to calculate precise distance traveled in applications like robot wheels. Or you can simply use the rotating shaft as an input device which navigates menus or settings.

This concept is a good one to understand. We had originally planned to build rotary encoders for the multi-person Duck Hunt at Hackaday’s 10th Anniversary but the build-off crew had difficulty getting the system to work. In [Pete’s] case he’s using photointerrupters (apparently the IR beam is easily detected through the white paper but usually these parts would be cut out of the disk). We were using reflectance sensors. Either way there’s a trick to detecting which direction a rotary encoder is turning. We’ll explain that for you after the break.

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Use a Cheap PIN Diode as a Geiger Counter

After the Fukushima nuclear power plant disaster, radiation measurement became newly relevant for a lot of people. Geiger-Müller tubes, previously a curiosity, became simultaneously important and scarce.

Opengeiger.de (English-language version here) has complete instructions for making a Geiger counter without a Geiger-Müller tube. Instead, this counter uses a PIN photodiode and some carefully chosen operational amplifiers. The total cost of such a device is significantly cheaper than the alternative: under $1 for the diode and around $5 for the rest. And since the PIN photodiode in question is used in many other devices, it’s not a niche component like a Geiger tube is.

The secret sauce is in component selection and tuning. Opengeiger uses the BPW34 diode because it is relatively common and has a large surface area, but also because it has a very low capacitance when reverse-biased. The first-stage opamp choice is also fairly critical. Considering that an average gamma radiation event produces only around 10 nanoamps for about 50 microseconds, a lot of amplification (100,000x), low noise, and high bandwidth are a must.

If you want to get started with this project, you could first browse through the explanation (PDF) to get an overview of the project’s goals, read up on all the technical considerations (PDF) or just head straight for the DIY instructions for the “Stuttgarter Geigerle” (PDF, schematic is on the last page). All of the documentation is chock-full of relevant references and totally worth the read.

How To Reverse Engineer, Featuring the Rigol DS1054Z

For a few years now, the Rigol DS1052E has been the unofficial My First Oscilloscope™. It’s cheap, it’s good enough for most projects, and there have been a number hacks and mods for this very popular scope to give it twice as much bandwidth and other interesting tools. The 1052E is a bit long in the tooth and Rigol has just released the long-awaited update, the DS1054Z. It’s a four-channel scope, has a bigger screen, more bells and whistles, and only costs $50 more than the six-year-old 1052E. Basically, if you’re in the market for a cheap, usable oscilloscope, scratch the ~52E off your list and replace it with the ~54Z.

With four channels of input, [Dave Jones] was wondering how the engineers at Rigol managed to stuff two additional front ends into the scope while still meeting the magic price point of $400. This means it’s time for [Dave] to reverse engineer the 1054Z, and give everyone on the Internet a glimpse at how a real engineer tears apart the worth of other engineers.

The first thing [Dave] does once the board is out of the enclosure is taking a nice, clear, and in-focus picture of both sides of the board. These pictures are edited, turned into a line drawing, and printed out on a transparency sheet. This way, both sides of the board can be viewed at once, allowing for a few dry erase marker to highlight the traces and signals.

Unless your voyage on the sea of reverse engineering takes you to the island of despair and desoldering individual components, you’ll be measuring the values of individual components in circuit. For this, you’ll want a low-voltage ohms function on your meter; if you’re putting too much voltage through a component, you’ll probably turn on some silicon in the circuit, and your measurements will be crap. Luckily, [Dave] shows a way to test if your meter will work for this kind of work; you’ll need another meter.

From there, it’s basically looking at datasheets and drawing a schematic of the circuit; inputs go at the left, outputs at the right, ground is at the bottom, and positive rails are at the top. It’s harder than it sounds – most of [Dave]’s expertise in this area is just pattern recognition. It’s one thing to reverse engineer a circuit through brute force, but knowing the why and how of how the circuit works makes things much easier.

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Think Before You Measure – Old Test Gear and Why It Is Awesome

Good, workable test gear is key to enabling our hobby. In this post we will discuss where to procure it at rock-bottom prices, what to look for, how to fix it, and how to tailor your laboratory practices around gear that may not be reliable.

We are lucky to be living in an era with plentiful high-quality test gear. Since the Second World War, surplus test gear has been in abundance at low costs enabling hobbyists, innovators, and academics to experiment and build great things. If you are willing to think before you measure you can save serious amounts of money and have a professional laboratory in your home.

Where to buy
The obvious answer is eBay, but the deals on test equipment are at the hamfests. Don’t be fooled by the name. Hamfests sell much more than amateur radio equipment. Hamfests are swap meets where hobbyists trade electronics of all kinds. Check out the ARRL hamfest calendar to find the next local one near you! I suggest you arrive early, however. The culture of hamfests tends to favor showing up as soon as the doors open and leaving about two hours before the official end. The early bird gets the worm!

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Palatable Pallet Procurement Procedures

Wooden pallets are a versatile and widely-available starting point for a multitude of projects. Best of all, they can usually be acquired free of charge. But choose the wrong kind of pallet and you could end up paying dearly. [Eric] has compiled a great deal of useful information about pallets that will help you find ideal candidates and prepare them for whatever project you have in mind, be it a coffee table or a backyard roller coaster.

Pallets come in several styles and loader configurations. Some are made with space between the boards, and others are closed. If you take nothing else away from his article, just remember to look for plain, untinted pallets with no markings and you’ll be fine.

No markings means the pallet was used domestically, so markings aren’t required. Marked pallets from abroad should feature the IPPC logo as well as a treatment code indicating the method used on the material. Debarked (DB), heat treated (HT), and pallets with the European Pallet Association logo (EPAL) are all safe choices. Pallets labeled (MB) were treated with methyl bromide, which is a poisonous fungicide. Colored pallets should be avoided as well. If you find one in a cool color, take a picture of it and find some paint in a similar hue.

Safe pallets can be had from many places ranging from hardware stores to feed and tack supply stores. Find someone you can ask for permission to take pallets—they might even help you load them. Keep some gloves in your trunk to avoid splinters.