Visually Tune Your HF Antenna Using An Oscilloscope And Signal Generator

September 20, 2013 by 15 Comments

Lots of readers are into toying around with RF and ham radios. One thing that is always of concern is tuning the antenna. New equipment is never cheap, so whenever another option comes along that uses existing test gear it gets our attention. [Alan Wolke] aka [w2aew] covers a process he uses to tune his HF antenna using a signal generator and oscilloscope.

The process is more of a teaching aid than a practical replacement for commercial equipment mostly because proper signal generators and oscilloscopes are large items and sometimes not available or affordable. That said, if you do have such test gear you only need build a simple breakout board containing a form of wheatstone bridge where the unknown Rx is the antenna. Two oscilloscope probes are connected across the bridge balance nodes. Some special care needs to be taken matching probe cable length and 50 ohm input impedance to the oscilloscope. A couple of 1K probe coupling resistors are also needed to prevent affecting the impendence at the hookup points. Once the selected signal is injected you can adjust an antenna tuner until the two voltage waveforms match on the oscilloscope indicating your antenna network is tuned to 50 ohm impedance with no reactance.

Being able to tune your antenna visually can really help you understand what is going on in the turning process; matching not only input impedance but also phase shift indicating inductive or capacitive reactance. Join us after the break to see the video and for information on what’s presented in the second part of [Alan’s] presentation.

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DIY Ultrasonic Acoustic Levitation

September 20, 2013 by 22 Comments

[Mike] saw a few videos of ultrasonic acoustic levitation rigs put together by student researchers. Figuring it couldn’t be that hard to replicate, he set out and built his own using surplus parts and whatever was sitting around his parts drawer.

The build began with a huge ultrasonic transducer from an old ultrasonic cleaning tank [Mike] picked up on eBay for $20 £20. He didn’t pick up the standard driver board, as those don’t have a very clean output – something desperately needed if you’re setting up a standing wave. He did manage to put a simple supply together with a 555 timer, a MOSFET and a 12 V transformer connected backwards, though.

The test rig is pretty simple – just the transducer sitting on a table with an aluminum plate sitting above it on threaded rods. By adjusting the distance between the transducer to the aluminum plate, [Mike] managed to set up some standing waves he was able to suspend small Styrofoam balls in. It’s not quite precise enough to levitate small chunks of sodium and water, but it makes for an excellent science fair-type project.

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Mario Plays Piano With A Little Help From Raspberry Pi

September 20, 2013 by 9 Comments

mario-piano

[David] has created his own live robot band to play live versions of the music and sound effects of NES games. Most of us who grew up in the 80’s and 90’s have the music of Nintendo games burned into our brains. While there have been some amazing remixes created over the years, [David] has managed to do something truly unique. Armed with an emulator, some software prowess, and a pair of Raspberry Pis, [Dave] created a system that plays game music and sound effects on analog instruments. A Yamaha Disklavier player piano handles most of the work through a connection to a Raspberry Pi. Percussion is handled by a second Pi.  Snare drum, wood block, and tambourine are all actuated by a custom solenoid setup.

The conversion process all happens on the fly as the game is played. [Dave] says the process has about ½ second of lag when played live, but we’re sure that could be fixed with some software tweaks. Continue reading “Mario Plays Piano With A Little Help From Raspberry Pi” →

Advanced Transcend WiFi SD Hacking: Custom Kernels, X, And Firefox

September 19, 2013 by 95 Comments

[Dmitry] read about hacking the Transcend WiFi cards, and decided to give it a try himself.   We already covered [Pablo’s] work with the Transcend card. [Dmitry] took a different enough approach to warrant a second look.

Rather than work from the web interface and user scripts down, [Dmitry] decided to start from Transcend’s GPL package and work his way up. Unfortunately, he found that the package was woefully incomplete – putting the card firmly into the “violates GPL” category. Undaunted, [Dmitry] fired off some emails to the support staff and soldiered on.

It turns out the card uses u-boot to expand the kernel and basic file system into a ramdisk. Unfortunately the size is limited to 3MB. The limit is hard-coded into u-boot, the sources of which transcend didn’t include in the GPL package.

[Dmitry] was able to create his own binary image within the 3MB limit and load it on the card. He discovered a few very interesting (and scary) things. The flash file system must be formatted FAT32, or the controller will become very upset. The 16 (or 32)GB of flash is also mounted read/write to TWO operating systems. Linux on the SD card, and whatever host system the card happens to be plugged in to. This is dangerous to say the least. Any write to the flash could cause a collision leading to lost data – or even a completely corrupt file system. Continue reading “Advanced Transcend WiFi SD Hacking: Custom Kernels, X, And Firefox” →

Desoldering Chips With Fire

September 19, 2013 by 29 Comments

Salvaging components is a staple of any electronic enthusiast, but many times those interesting chips – old 8-bit microcontrollers, memories, and CPUs found in everything from game consoles to old computers – are rather difficult to remove from a board. [Ryan] over on Instructables has a rather interesting method of removing old SMD packages using nothing more than a little fire and a pair of tweezers.

Obviously the best way to go about salvaging SMD components is with a heat gun, but lacking the requisite equipment, [Ryan] managed to remove a few SMD chips using rubbing alcohol as a heat source. In a properly controlled environment, [Ryan] filled a small metal dish with alcohol, set it on fire, and used the heat generated to remove a few components. Alcohol lamps are a common bench tool in a range of repair disciplines because the fuel is cheap and burns relatively cleanly (not leaving an unwanted residue on the thing you’re heating).

It’s an interesting kludge, and given [Ryan]’s display of desoldered components, we’re going to call it a success. It might also work for through-hole components, allowing for easy removal of old SRAM, ROM, and other awesome chips.

BeagleBone Black Does CNC With RAMPS

September 19, 2013 by 13 Comments

[Bart] Wanted to try controlling a CNC with his BeagleBone black, but didn’t want to invest in a CNC Cape. No problem – he created his own translator board for RAMPS. LinuxCNC for the BeagleBone Black has been available for a few months now, and [Bart] wanted to give it a try. He started experimenting with a single stepper motor and driver.  By the time he hooked up step, direction, and motor phases, [Bart] knew he needed a better solution.

Several CNC capes are available for the BeagleBone boards, but [Bart] had a RAMPS board just sitting around, waiting for a new project.  Most RepRap fans have heard of the RAMPS – or Reprap Arduino Mega Pololu Shield.  In fact, we covered them here just a few days ago as part of our 3D Printering series.   RAMPS handle all the I/O needed for 3D printing, which carries over quite nicely to other CNC applications as well.   The downside is that they’re specifically designed for the Arduino Mega series. Continue reading “BeagleBone Black Does CNC With RAMPS” →

Fail Of The Week: Smoking Pulse Sensor And BLE Disappointment

September 19, 2013 by 12 Comments

fotw-ble-and-pulse-sensor

We think [Thomas Brittain] is onto something. We often post to our personal blogs so that we have a reference to how we did something. But he also keeps a long post that documents his abandoned projects. It ends up serving as a quick start if he ever decides to pick up the torch once again. Lucky for us he’s included his failures in the write up. This Fail of the Week features the top two posts on his Incomplete Works page. The first is an attempt to make his own pulse sensor. The second is a miserable experience with a cheap Bluetooth Low Energy module.

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