Category Archives: fft

SDR Is At the Heart of This Soup-Can Doppler Radar Set

Posted on by

Want to explore the world of radar by feel daunted by the mysteries of radio frequency electronics? Be daunted no more and abstract the RF complexities away with this tutorial on software-defined radar.

Taking inspiration from our own [Gregory L. Charvat], whose many radar projects have graced our pages before, [Luigi Freitas]’ plunge into radar is spare on the budgetary side but rich in learning opportunities. The front end of the radar set is almost entirely contained in a LimeSDR Mini, a software-defined radio that can both transmit and receive. The only additional components are a pair of soup can …read more

Continue reading SDR Is At the Heart of This Soup-Can Doppler Radar Set→

Big Mouth Billy Bass Channels Miley Cyrus

Posted on by

Here’s a Big Mouth Billy Bass with extra lip thanks to Alexa. If you’re not already familiar, Big Mouth Billy Bass is the shockingly popular singing animatronic fish designed to look like a trophy fish mounted to hang on your wall. In its stock condition, Billy uses a motion sensor to break into song whenever someone walks by. It’s limited to a few songs, unless you like to hack things — in which case it’s a bunch of usable parts wrapped in a humorous fish! Hackaday’s own [Bob Baddeley] combined the fish with an Amazon Echo Dot, connecting the two …read more

Continue reading Big Mouth Billy Bass Channels Miley Cyrus→

The Tachometer Inside Your Smartphone

Posted on by

It’s the latest in instrumentation for the well-appointed shop — an acoustically coupled fast Fourier transform tachometer. Sounds expensive, but it’s really just using a smartphone spectrum analyzer app to indirectly measure tool speeds. And it looks like it could be incredibly handy.

Normally, non-contact tachometers are optically coupled, using photoreceptors to measure light flashing off of a shaft or a tool. But that requires a clear view of the machine, often putting hands far too close to the danger zone. [Matthias Wandel]’s method doesn’t require line of sight because it relies on a cheap spectrum analyzer app to listen …read more

Continue reading The Tachometer Inside Your Smartphone→

Making a Cheap Radar Unit Awesome

Posted on by

[JBeale] squeezed every last drop of performance from a $5 Doppler radar module, and the secrets of that success are half hardware, half firmware, and all hack.

On the hardware side, the first prototype radar horn was made out of cardboard with aluminum foil taped around it. With the concept proven, [JBeale] made a second horn out of thin copper-clad sheets, but reports that the performance is just about the same. The other hardware hack was simply to tack a wire on the radar module’s analog output and add a simple op-amp gain stage, which extended the sensing range well …read more

Continue reading Making a Cheap Radar Unit Awesome→

Listen To Your Fermentation To Monitor Its Progress

Posted on by

If you are a wine, beer, or cider maker, you’ll know the ritual of checking for fermentation. As the yeast does its work of turning sugar into alcohol, carbon dioxide bubbles froth on the surface of your developing brew, and if your fermentation container has an airlock, large bubbles pass through the water within it on a regular basis. Your ears become attuned to the regular “Plop… plop… plop” sound they make, and from their interval you can tell what stage you have reached.

[Chris] automated this listening for fermentation bubbles, placing a microphone next to his airlock and detecting …read more

Continue reading Listen To Your Fermentation To Monitor Its Progress→

Voice at 700 Bits Per Second

Posted on by

All other things being equal, signals with wider bandwidth can carry more information. Sometimes that information is data, but sometimes it is frequency. AM radio stations (traditionally) used about 30 kHz of bandwidth, while FM stations consume nearly 200 kHz. Analog video signals used to take up even more space. However, your brain is a great signal processor. To understand speech, you don’t need very high fidelity reproduction.

Radio operators have made use of that fact for years. Traditional shortwave broadcasts eat up about 10kHz of bandwidth, but by stripping off the carrier and one sideband, you can squeeze the …read more

Continue reading Voice at 700 Bits Per Second→

Making a Spectrum Analyzer the Wrong Way on an ATtiny85

Posted on by

Everyone’s a critic, but it’s hard to argue with success. And that’s exactly what [agp.cooper] has with his ATtiny85-based spectrum analyzer devices.

The “normal” way to build a spectrum analyzer is to collect a bunch of samples and run a Fast Fourier Transform (FFT) on them all in one shot. As the name implies, the FFT is fast, and the result is the frequency components of the sampled data. [agp.cooper]’s “wrong” way to do it takes the Goertzel algorithm, which is used for detecting the intensity of a particular frequency, and scanning across the frequency range of interest. It’s a …read more

Continue reading Making a Spectrum Analyzer the Wrong Way on an ATtiny85→

Tearing into Delta Sigma ADCs Part 2

Posted on by

In part one, I compared the different Analog to Digital Converters (ADC) and the roles and properties of Delta Sigma ADC’s. I covered a lot of the theory behind these devices, so in this installment, I set out to find a design or two that would help me demonstrate the important points like oversampling, noise shaping and the relationship between the signal-to-noise ratio and resolution.

Modulator Implementation

Check out part one to see the block diagrams of what what got us to here. The schematics shown below are of a couple of implementations that I played with depicting a single-order …read more

Continue reading Tearing into Delta Sigma ADCs Part 2→

Tearing into Delta Sigma ADCs Part 2

Posted on by

In part one, I compared the different Analog to Digital Converters (ADC) and the roles and properties of Delta Sigma ADC’s. I covered a lot of the theory behind these devices, so in this installment, I set out to find a design or two that would help me demonstrate the important points like oversampling, noise shaping and the relationship between the signal-to-noise ratio and resolution.

Modulator Implementation

Check out part one to see the block diagrams of what what got us to here. The schematics shown below are of a couple of implementations that I played with depicting a single-order …read more

Continue reading Tearing into Delta Sigma ADCs Part 2→

Tearing into Delta Sigma ADC’s

Posted on by

It’s not surprising that Analog to Digital Converters (ADC’s) now employ several techniques to accomplish higher speeds and resolutions than their simpler counterparts. Enter the Delta-Sigma (Δ∑) ADC which combines a couple of techniques including oversampling, noise shaping and digital filtering. That’s not to say that you need several chips to accomplish this, these days single chip Delta-Sigma ADCs and very small and available for a few dollars. Sometimes they are called Sigma-Delta (∑Δ) just to confuse things, a measure I applaud as there aren’t enough sources of confusion in the engineering world already.

I’m making this a two-parter. I  …read more

Continue reading Tearing into Delta Sigma ADC’s→