Filtering Out Mains Hum From ADC Samples

July 15, 2013 by Mike Szczys 19 Comments

Hum_filter

A little light reading means something different to us than it does to [Hamster]. He’s been making his way through a book called The Scientist and Engineer’s Guide to Digital Signal Processing written by [Steven W. Smith, Ph.D]. Being the hacker type, a million different uses for the newfound knowledge popped to mind. But as a sanity check he decided to focus on a useful proof of concept first. He’s come up with a way to filter out the mains hum from Analog to Digital Converter samples.

Mains hum is all around us; produced by the alternating current in the power grid that runs our modern lives. It’s a type of interference that can be quite problematic, which is on reason why we see EMF sensor projects from time to time. Now you can filter that ambient interference from your projects which take readings from an ADC. This would be quite useful for applications which measuring teeny signals, like ECG hacks.

[Hamster] did a pretty good job of presenting his demonstration for the uninitiated. He even provides examples for Arduino or FPGA projects.

Guitar Foot Controller Uses DSP For Audio Effects

November 30, 2012 by Mike Szczys 7 Comments

guitar-pedal-dsp1

This a screenshot taken from [Pierre’s] demonstration of an electric guitar effects pedal combined with DSP and Pure Data. He pulls this off by connecting the guitar directly to the computer, then feeds the computer’s audio output to the guitar amp.

The foot controls include a pedal and eight buttons, all monitored by an Arduino. Pure Data, a visual programming language, interprets the input coming from the Arduino over USB and alters the incoming audio using digital signal processing. [Pierre] manages the audio connection using the JACK Audio Connection Kit software package.

In the video after the break he’s using a laptop for most of the work, but he has also managed to pull this off with a Raspberry Pi. There’s no audio input on the RPi board, but he’s been using a USB sound card anyway. The other USB port connects the Arduino and he’s in business.

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Frequency Analyzer Built From The New Stellaris Launchpad

September 6, 2012 by Mike Szczys 79 Comments

Here’s the first project we’ve seen for the new Stellaris Launchpad. It’s a frequency analyzer which displays a graph on an 8×8 LED module. What’s that you say? You haven’t received your new Launchpad board yet? Neither have we since they don’t start shipping until the end of the month. But [EuphonistiHack] works as a software dev for TI and snagged one of the early development units.

Hardware is rather simple. He uses an OpAmp to feed audio from his laptop to the ARM processor. The 8×8 LED module is an MSP430 booster pack that is addressed via SPI. On the software side of things he’s really taking advantage of hardware peripherals to simplify his work. A timer triggers each ADC reading which in turn writes the values using uDMA. Digital Signal Processing (available as a CMSIS library for many ARM chips) is then used to translate the ADC value to one that can be displayed on the LEDs. Check out the video after the break to see the final version.

The Hackaday writers are looking for an easier name for this hardware than “Stellaris Launchpad”. It doesn’t seem to lend itself to a shorter name, like RPi or Raspi does for the Raspberry Pi. If you’ve got a catchy nick name for the new board please share it in the comments.

Playing With DSP And Building A Guitar Pedal

August 23, 2012 by Brian Benchoff 19 Comments

Building guitar pedals has come a long way from hooking up a few transistors and building a simple boost circuit. [Cloudscapes] has been working on a Anti-nautilus auto glitch, auto repeat pedal, and if you’re looking for something that sounds like a spaghetti western soundtrack skipping on a record player, we couldn’t think of anything better.

[Cloudscapes] was already familiar with 8-bit AVRs, but when doing real-time audio sampling, a more powerful microcontroller was in order. He turned to the MikroElektronika MINI-32 board for development purposes. This small board fits a PIC32 microcontroller into an easily breadboardable DIP-40 form factor, perfect for playing around with some very capable hardware.

For the DAC, [Cloudscapes] had some experience with the 16-bit PT8211, but finding a good 16-bit ADC in a convenient package was a bit of a challenge. He eventually settled on the 12-bit MCP3201 ADC, more than enough for a pedal that is supposed to sound lo-fi.

After [Cloudscapes] got a few boards made, he started on his DSP adventure. Unfortunately, the initial code used unsigned 16-bit words to represent each sample, meaning every time the loop repeated it would start at 0 and produce a short pop in the speaker. After a week of debugging, [Cloudscapes] realized signed integers are a much better data format for storing audio data and got rid of the problems plaguing his project.

Now [Cloudscapes] has a wonderful DSP dev board, perfect for making new and strange guitar effects. After the break you can listen to a demo of what the Anti-nautilus pedal actually does, and we’ve got to say it sounds great.

Thanks [Chris] for sending this one in.

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Building A Digital Camera From Scratch

November 28, 2011 by Brian Benchoff 25 Comments

Sure, [Stan] could have bought a nice full-frame DSLR like a Canon 5D or a Nikon D3, but where’s the fun in that when he could build his own digital camera? The build isn’t done yet, but [Stan] did manage to take a few sample pics.

The 14 Megapixel sensor [Stan] found was originally used for benchtop applications. There isn’t any reason it can’t be used for photography, so all that needed to be done was design a camera around this sensor.

[Stan] built his hardware around a DSP, an FPGA and a pair of ADCs, an amazing piece of engineering. Of course building a full-frame digital camera has as much to do with mechanics as electronics, so [Stan] used a 60mm cage system and a 3d-printed nylon enclosure.

Of course, [Stan]’s camera doesn’t look much like and off-the-shelf DSLR. There’s a reason for this; the sensor in the camera has a rolling shutter, much like the last few iPhones instead of a focal plane shutter. Not a bad piece of work, we only wish there were more build pics.

Halloween Props: Voice-changing Daft Punk Costume

October 31, 2010 by Mike Szczys 6 Comments

[Dr. West] shared his Halloween costume with us; a Daft Punk inspired voice-changing helmet. He stared with a motorcycle helmet, cutting out a hole in the back for a sub-woofer speaker. Inside there’s an old computer mic and the amp circuitry for a portable stereo system. An Arduino is used to pick up the wearer’s voice from the microphone and perform the digital signal processing. Once the alterations have been made the signal is sent to an R-2R resistor ladder to perform the digital to analog conversion, and onto the amp for broadcast. Hear the result in the video after the break.

The rest of the helmet is window dressing. He found some kind of auto-body repair product called flex-edging to use as metallic hair. Those fins are accented with strings of red and blue LEDs. The faceplate finishes the look using speakers from the stereo system and a tinted visor.

He wan’t going for a replica, but we think his creation would be right at home with the look of the original.

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QRSS: Radio Amateurs’ Slow-speed Narrowband

February 22, 2009 by Eliot 30 Comments

qrss

Host of the Soldersmoke podcast, [Bill Meara], contributed this guest post.

While the rest of the world is moving toward high speed broadband, some hams—including one Nobel Prize winner—are going in exactly the opposite direction. Our ‘QRSS’ mode makes use of an unusual mixture of modern digital signal processing (DSP), ancient Morse code, and simple homebrewed transmitters. Very narrow bandwidth is desirable because this reduces the noise in the radio communication channel, greatly improving the S/N ratio. But Shannon’s communication theory tells us that narrow bandwidth comes with a cost: slow data rates. In QRSS, beacon transmitters using only milliwatts churn out slow speed Morse ID signals on 10.140 MHz that are routinely picked up by DSP-based receivers on the other side of the globe. Many of the receivers, ‘grabbers’, have visual outputs that are available online in real time. QRSS has been getting a lot of attention on the Soldersmoke podcast and on the Soldersmoke Blog. For more information check out this overview and the hardware involved. Here’s a gallery of received signals.