Advent Calendar – ‘Tis The CNSeason

December 8, 2018 by 3 Comments

CNC machines are powerful tools when used correctly, but it’s often necessary to test a new machine before getting into serious production work. This advent calendar is a great festive project that was designed to put a CNC through its paces.

The calendar is made primarily from wood. This is an excellent choice for test machining projects, as it is softer and less likely to cause tool or machine damage when compared to steel or aluminum. The calendar base was first milled out using end mills, while a 30-degree V-bit was used to engrave the days of the week. Brass brazing rod was then used to create hangers for the calendar tags.

Thanks to the clever use of chalkboard paint and removable tags, the calendar can be reconfigured to work for any given year and month combination — just in case you wish to have an advent calendar year round. Overall, it’s a good low-intensity machining project that would also be a fun craft project for kids.

As it’s that time of year, you might like this blinky advent calendar, too. Video after the break.

[Thanks to Michael for the tip!]

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Crystal Oscillators Explained

December 8, 2018 by 13 Comments

We’ve read a lot about oscillators, but crystal oscillators seem to be a bit of a mystery. Hobby-level books tend to say, build a circuit like this and then mess with it until it oscillates. Engineering texts tend to go on about loop gains but aren’t very clear about practice. A [circuit digest] post that continues a series on oscillators has a good, practical treatment of the subject.

Crystals are made to have a natural resonant frequency and will oscillate at that frequency or a multiple thereof with the proper excitation. The trick, of course, is finding the proper excitation.

The post starts with a basic model of a crystal having a series capacitance and inductance along with a resistance. There’s also a shunt or parallel capacitor. When you order a crystal, you specify if you want the resonant frequency in series or parallel mode — that is, which of the capacitors in the model you want to resonate with the inductor — so the model has actual practical application.

By applying the usual formula for resonance on the model you’ll see there is a null and a peak which corresponds to the two resonance points. The dip is the series frequency and the peak is the parallel. You can actually see a trace for a real crystal in a recent post we did on the Analog Discovery 2. It matches the math pretty well, as you can see on the right.

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The Guts Of Switched Mode Power Supplies, Brought To You By Oscilloscope Repair

December 8, 2018 by 22 Comments

The Tektronix 2000 series of oscilloscopes are a mainstay for any electronics lab. They work, they’re relatively cheap, they’re good, and they’re available in just about any surplus electronics store. [Mr.RC-Cam] has been hoarding one of these for twenty years, and like any classic piece of equipment, it needs a little refurbishment every now and again. Now, it’s time. Here’s how you repair one of the best values in analog oscilloscopes.

This repair adventure began when the scope died. There were no lights, no screen trace, and a brief hiss sound when it was powered on. (Ten points if you can guess what that hiss sound was!) Armed with a schematic, [Mr.RC-Cam] dove in and pulled the power supply, being careful to discharge the CRT beforehand.

There were no bulging capacitors, no obviously overheated components, and just a little bit of dust. The only solution was to look at the parts with a meter one at a time. Removing the big caps provided access to a row of diodes, which revealed the culprit: a single shorted diode. This part was ordered, and a few other housekeeping tasks were taken care of. The lithium battery on the processor board responsible for storing the calibration constants was replaced, and the new, smaller, caps got lovely 3D printed mounting flange adapters. Now, this old ‘scope works, and we’ve got a lovely story to tell around the electronic campfire.

Negative Voltage Pushes AVR To New Heights

December 8, 2018 by 38 Comments

If we say that a hacker is somebody who looks at a “solved” problem and can still come up with multiple alternative solutions, then [Charles Ouweland] absolutely meets the grade. Not that we needed more evidence of his hacker cred given what we’ve seen from him before, but he recently wrote in to tell us about an interesting bit of problem solving which we think is a perfect example of the principle. He wanted to drive a salvaged seven segment LED display with an AVR microcontroller, but there was only one problem: the display needs 15V but the AVR is only capable of 5V. So what to do?

As it turns out, the first step to solving the problem was verifying there was actually a problem to begin with. [Charles] did some experimentation and found that the display didn’t actually need 15V to operate, and in fact would light up well enough at just 6.5V. This lowered the bar quite a bit, but it was still too high to power directly from the chip.

There were a few common ways to solve this problem, which no doubt the Hackaday reader is well aware of. But [Charles] wanted to take the path less traveled. More specifically, the path with the least amount of additional components he had to put on his PCB. He set out to find the absolute easiest way to make his 5V AVR light up a 6.5V LED, and ended up coming with a very clever solution that some may not even know is possible.

He reasoned that if he connected the source pins of two BS170 MOSFETs to a voltage of -1.5V, even when the AVR pin was 0V, they would be still be receiving 1.5V. This virtual “step ladder” meant that once the AVR’s pin goes high (5V), the relative voltage would actually be 6.5V and enough to drive his LEDs. Of course the only problem with that is that you need to have a source for -1.5V.

Getting a negative voltage would normally require adding more components to the design (which he set out to avoid in the first place), but then he came up with another clever idea. To pull the trick off, he actually feeds the AVR 6.5V, but raises the ground voltage by 1.5V with the addition of two 1N4007 diodes. This way the AVR gets a voltage within its capabilities and still can provide a relative 6.5V to the LEDs.

One might say [Charles] took the Kobayashi Maru approach, and simply redefined the rules of the game. But such is the power of the confounding negative voltage.

NTP Morse Code Clock Powered By ESP8266

December 8, 2018 by 6 Comments

We’ve featured a great many unique clocks here on Hackaday, which have utilized nearly every imaginable way of conveying the current time. But of all these marvelous timepieces, the Morse code clock has the distinct honor of simultaneously being the easiest to construct and (arguably) the most difficult to read. As such, it’s little surprise we don’t see them very often. Which makes this latest entry into the field all the more interesting.

[WhisleyTangoHotel] has taken the basic concept of the Morse clock, which at its most simplistic could be done with a microcontroller and single LED, and expanded it into a (relatively) practical device. With both audio and visual signaling, and support for pulling the time from NTP, this is easily the most polished Morse code clock we’ve ever seen. Using it still requires you to have a decent grasp on Samuel Morse’s now nearly 200 year old encoding scheme of course, but on the bright side, this clock is sure to help keep your CW skills sharp.

For those following along at home, [WhisleyTangoHotel] provides a hand-drawn diagram to show how everything connects together in his Morse timepiece, but there’s nothing on the hardware side that’s likely to surprise the Hackaday reader. A single momentary push button represents the device’s sole user input, with the output being handled by a LED “tower” and speaker on their own respective pins on the microcontroller. Here a Adafruit Feather HUZZAH is used, but any ESP8266 would work in its place.

Of course, the advantage of using an ESP8266 board over your garden variety MCU is the Wi-Fi connectivity. This allows the clock to connect to an NTP server and get the current time before relaying it to the user. Some might think this overkill, but it’s really a critical feature; the lack of a proper RTC on the ESP means the clock would drift badly if not regularly synchronized. Assuming you’ve got a reliable Internet connection, this saves you the added cost and complexity of adding an external RTC.

[WhisleyTangoHotel] wraps up his blog post by providing his ESP8266 Arduino source code, which offers an interesting example in working not only with NTP and time zones on the ESP, but how to handle parsing strings and representing their principle characters in Morse code.

Interestingly enough, in the past we’ve seen a single LED clock that didn’t use Morse code to blink out the time, which might be a viable option as an alternate firmware for this device if you’re not in the Samuel Morse fan club.

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VexRISC-V Exposed

December 8, 2018 by 8 Comments

If you want to use FPGAs, you’ll almost always use an HDL like Verilog or VHDL. These are layers of abstraction just like using, say, a C compiler is to machine language or assembly code. There are other challengers to the throne such as SpinalHDL which have small but enthusiastic followings. [Tom] has a post about how the VexRISC-V CPU leverages SpinalHDL to make an extremely flexible system that is as efficient as plain Verilog. He says the example really shows off why you should be using SpinaHDL.

Like a conventional programming language, it is easy to find niche languages that will attract a little attention and either take off (say, C++, Java, or Rust) or just sort of fade away. The problem is you can’t ever tell which ones are going to become major and which are just flashes in the pan. Is SpinalHDL the next big thing? We don’t know.

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Wearable Speeder Bikes Are Ready For A Night Out

December 7, 2018 by 8 Comments

While Hackaday is about as far from a fashion blog as you can possibly get, we have to admit we’re absolutely loving the [bithead942] Winter 2018 Collection. His wife and daughter recently got to model his latest must have design: wearable Star Wars speeder bikes; and judging by the video after the break they were certainly some of the best dressed at the Thanksgiving parade.

[bithead942] started the build by taking careful measurements of a vintage speeder bike model kit his wife had, which allowed to accurately recreate the iconic look of the vehicles as they were seen in Return of the Jedi . But to do them justice, the final “bikes” would need to be around three meters (ten feet) long, which immediately posed a problem. What kind of material could support itself over that length while still being light enough to wear for extended periods of time?

The answer came, as it often does, from the local hardware store. He found that a combination of Schedule 80 and 40 PVC pipe was a perfect material: strong enough to support the desired dimensions without bending, light enough that the final bike wouldn’t be uncomfortable to wear, easy to bend with heat, and perhaps best of all, cheap and readily available. The PVC frame was then covered with chicken wire and thin flexible foam to give it a filled out look without weighing them down.

Even though he had a strict weight limit on the build, [bithead942] couldn’t help but add in some electronics to complete the effect. The LED festooned control panel allows the ladies to trigger different sound effects from the movie stored on a Adafruit Mini FX Sound Board, which is connected to a 20W Class D amplifier and a pair of 400 watt car stereo speakers. He says the resulting playback was loud enough to hear outside during the parade, and only added a few pounds to the overall build.

These may be the bikes you’re looking for, but they’re definitely not the first we’ve featured on Hackakday. Meanwhile you’d be wise not to underestimate the lowly PVC pipe when designing your next project. From a hacked together drill press for your Dremel to a planetarium for you and your closest dozen or so friends, there’s little you can’t build with this plentiful material.

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