Blindingly Fast ADC For Your BeagleBone

July 31, 2016 by Elliot Williams 28 Comments

[Jason Holt] wrote in to tell about of the release of his PRUDAQ project. It’s a dual-channel 10-bit ADC cape that ties into the BeagleBone’s Programmable Realtime Units (PRUs) to shuttle through up to as much as 20 megasamples per second for each channel. That’s a lot of bandwidth!

The trick is reading the ADC out with the PRUs, which are essentially a little bit of programmable logic that’s built on to the board. With a bit of PRU code, the data can be shuttled out of the ADC and into the BeagleBone’s memory about as fast as you could wish. Indeed, it’s too fast for the demo code that [Jason] wrote, which can’t even access the RAM that fast. Instead, you’ll want to use custom kernel drivers from the BeagleLogic project (that we’ve covered here before).

But even then, if you don’t want to process the data onboard, you’ve got to get it out somehow. 100 mbit Ethernet gets you 11.2 megabytes per second, and a cherry-picked flash drive can save something like 14-18 megabytes per second. But the two 10-bit ADCs, running full-bore at 20 megasamples per second each, produces something like 50-80 megabytes per second. Point is, PRUDAQ is producing a ton of data.

So what is this cape useful for? It’s limited to the two-volt input range of the ADCs — you’ll need to precondition signals for use as a general-purpose oscilloscope. You can also multiplex the ADCs, allowing for eight inputs, but of course not at exactly the same time. But two channels at high bandwidth would make a great backend for a custom SDR setup, for instance. Getting this much ADC bandwidth into a single-board computer is an awesome trick that used to cost thousands of dollars.

We asked [Jason] why he built it, and he said he can’t tell us. It’s a Google Research project, so let the wild conjecture-fest begin!

Hacklet 116 – Audio Projects

July 16, 2016 by Adam Fabio 5 Comments

If the first circuit a hacker builds is an LED blinker, the second one has to be a noisemaker of some sort. From simple buzzers to the fabled Atari punk console, and guitar effects to digitizing circuits, hackers, makers and engineers have been building incredible audio projects for decades. This week the Hacklet covers some of the best audio projects on Hackaday.io!

We start with [K.C. Lee] and Automatic audio source switching. Two audio sources, one amplifier and speaker system; this is the problem [K.C. Lee] is facing. He listens to audio from his computer and TV, but doesn’t need to have both connected at the same time. Currently he’s using a DPDT switch to change inputs. Rather than manually flip the switch, [K.C. Lee] created this project to automatically swap sources for him. He’s using an STM32F030F4 ARM processor as the brains of the operation. The ADCs on the microcontroller monitor both sources and pick the currently active one. With all that processing power, and a Nokia LCD as an output, it would be a crime to not add some cool features. The source switcher also displays a spectrum analyzer, a VU meter, date, and time. It even will attenuate loud sources like webpages that start blasting audio.

Next up is [Adam Vadala-Roth] with Audio Blox: Experiments in Analog Audio Design. [Adam] has 32 projects and counting up on Hackaday.io. His interests cover everything from LEDs to 3D printing to solar to hydroponics. Audio Blox is a project he uses as his engineer’s notebook for analog audio projects. It is a great way to view a hacker figuring out what works and what doesn’t. His current project is a 4 board modular version of the Big Muff Pi guitar pedal. He’s broken this classic guitar effect down to an input board, a clipping board, a tone control, and an output stage. His PCB layouts, schematics, and explanations are always a treat to view and read!

Next we have [Paul Stoffregen] with Teensy Audio Library. For those not in the know, [Paul] is the creator of the Teensy family of boards, which started as an Arduino on steroids, and has morphed into something even more powerful. This project documents the audio library [Paul] created for the Freescale/NXP ARM processor which powers the Teensy 3.1. Multiple audio files playing at once, delays, and effects, are just a few things this library can do. If you’re new to the audio library, definitely check out [Paul’s] companion project
Microcontroller Audio Workshop & HaD Supercon 2015. This project is an online version of the workshop [Paul] ran at the 2015 Hackaday Supercon in San Francisco.

Finally we have [drewrisinger] with DrDAC USB Audio DAC. DrDac is a high quality DAC board which provides a USB powered audio output for any PC. Computers these days are built down to a price. This means that lower quality audio components are often used. Couple this with the fact that computers are an electrically noisy place, and you get less than stellar audio. Good enough for the masses, but not quite up to par if you want to listen to studio quality audio. DrDAC houses a PCM2706 audio DAC and quality support components in a 3D printed case. DrDAC was inspired by [cobaltmute’s] pupDAC.

If you want to see more audio projects and hacks, check out our new audio projects list. See a project I might have missed? Don’t be shy, just drop me a message on Hackaday.io. That’s it for this week’s Hacklet, As always, see you next week. Same hack time, same hack channel, bringing you the best of Hackaday.io!

Isolated Voltage Measurements Through Frequency

July 16, 2016 by Elliot Williams 23 Comments

This one’s not a flashy hack, it’s a great piece of work and a good trick to have up your sleeve. Sometimes you’ve got a voltage difference that you’d like to measure, but either the ground potential is at a different level, or the voltages are too high for your lowly microcontroller.

There are tons of tricks with resistive voltage dividers that you can play. But if you want serious electrical isolation from the target, there’s only one way to go — an optocoupler. But optocouplers only really transmit digital signals, and [Giovanni Carrera] needed to measure an analog voltage.

Enter the voltage-to-frequency IC that does just what it says: produces a square wave with a frequency that’s proportional to the voltage applied. Pass this square wave through an optocoupler, and you can hit one side with voltages approaching lightning strikes without damaging the microcontroller on the other side. And you’re still able to measure the voltage accurately by measuring the frequency on the digital I/O pins of the microcontroller.

[Giovanni] built up and documented a nice circuit. He even tested it for linearity. If you’re ever in the position of needing to measure a voltage in a non-traditional way, you’ll thank him later.

Tearing Into Delta Sigma ADC’s

July 7, 2016 by Bil Herd 33 Comments

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 will be talking about some theory and show the builds that demonstrate Delta-Sigma properties and when you might want to use them.

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Using Missile Tech To See Like Predator

May 18, 2016 by Rud Merriam 30 Comments

[Artem Litvinovich] wanted to see by heat vision like in the Predator movies. He not only succeeded but went on to see in color, medium-wave IR, short-wave IR, and ultraviolet using a very unique approach since his effort began back in 2009.

He started with a box based on the basic pinhole camera concept. In the box is a physical X-Y digitizer moving a photodiode to collect the thousands of points needed to create a picture. First all he got, due to the high signal amplification, was the 60 cycle hum that permeates our lives. A Faraday cage around the box helped but metal foil around the sensor and amplifier finally eliminated the noise. Now he had pictures in the near infrared (NIR). Continue reading “Using Missile Tech To See Like Predator” →

Analog To Digital Converter (ADC): A True Understanding

May 5, 2016 by Bil Herd 65 Comments

Back in the day where the microprocessor was our standard building block, we tended to concentrate on computation and processing of data and not so much on I/O. Simply put there were a lot of things we had to get working just so we could then read the state of an I/O port or a counter.

Nowadays the microcontroller has taken care of most of the system level needs with the luxury of built in RAM memory and the ability to upload our code. That leaves us able to concentrate on the major role of a microcontroller: to interpret something about the environment, make decisions, and often output the result to energize a motor, LED, or some other twiddly bits.

Often the usefulness of a small microcontroller project depends on being able to interpret external signals in the form of voltage or less often, current. For example the output of a photocell, or a temperature sensor may use an analog voltage to indicate brightness or the temperature. Enter the Analog to Digital Converter (ADC) with the ability to convert an external signal to a processor readable value.

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Beyond Measure: Instrumentation Amplifiers

March 18, 2016 by Brandon Dunson 35 Comments

In the first article about measurement systems we looked at sensors as a way to bring data into a measurement system. I explained that a sensor measures physical quantities which are turned into a voltage with a variable conversion element such as a resistor bridge. There will always be noise in any system, and an operational amplifier (op-amp) can be used to remove some of that noise. The example we considered used an op-amp in a differential configuration that removes any disturbance signal that is common to both inputs of the op-amp.

But that single application of an op-amp is just skimming the surface of the process of bringing a real-world measurement of a physical quantity into a digital system. Often, you’ll need to do more work on the signal before it’s ready for sampling with a digital-to-analog converter. Signal conditioning with amplifiers is a deep and rich topic, so let me make it clear that that this article will not cover every aspect of designing and implementing a measurement system. Instead, I’m aiming to get you started without getting too technical and math-y. Let’s just relax and ponder amplifiers without getting lost in detail. Doesn’t that sound nice?

Continue reading “Beyond Measure: Instrumentation Amplifiers” →