Digital Audio on the Parallax Propeller

[Beth] had the idea for transmitting digital audio over S/PDIF on a Propeller a few years ago, but only just got around to a writeup. For that, we thank her.

The writeup has a marvelous walkthrough of the S/PDIF protocol and the problems associated with with generating the signal. S/PDIF is a relatively resource-intensive protocol – the signal is clocked at 64x the audio sample rate. That signal is doubled for biphase mark code, keeping everything in sync. [Beth] says the microcontroller would neet at least 24 MIPS of processing power just to generate the S/PDIF signal – processing audio would be another task altogether. Because of the processing power needed, and the weird clock rates needed, [Beth] decided to go with the Propeller. The implementation uses only one core of the Propeller, leaving another seven cores available for sound synthesis or even a visualization over VGA.

[Beth] admits this could be done with just about any microcontroller (although it would need to be clocked at a multiple of 4.096 MHz for a 32kHz audio stream), but we really appreciate the work that went into bit-banging this signal.

Video of [Nick] at Gadget Gangster playing around with digital audio on a Propeller after the break.

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Propeller proto board has you flying in no time


[Parker] was in need of a Propeller development board to make working on his projects easier. More often than not, when he needed to prototype something, he would pull the only one he had on hand from his home made pinball machine, and replace it when finished. This was time consuming and cumbersome, so he decided he needed a better way of doing things.

He looked into purchasing a Gadget Gangster proto board which allows you to use a Propeller much like an Arduino, complete with support for shields and the like. Unfortunately, they were sold out and he was in a hurry to finish up a project. Rather than wait, he decided to build his own proto board, which would be more flexible than the COTS version – allowing him to add things like an Analog to Digital converter without having to use a shield.

He looked around online and found some schematics to follow, and had his proto board constructed in no time. It gets the job done and looks quite clean, considering it was put together using perf board.

Keep reading to see a video walkthrough of the Propeller development board construction.

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Remote-controlled tank tread robot will walk the dog for you


Instructables user [IAMTHEBOT] recently finished building his robot which can be controlled by a human using an R/C transmitter, via a PC, or through its built-in object avoidance system. The robot doesn’t seem to have a name, though Johnny Five might be appropriate.

The robot was built using plenty of erector set parts, as well as a Lynx motion tank tread kit. The robot is crammed full of controllers, including a Propeller USB servo controller which operates the arms, and a pair of Parallax motor controllers to manage the tread movement. A pair of Parallax Stamp controllers are used to drive these controllers as well as to manage the remainder of the robot’s functions.

The robot’s head consists of a custom pan and tilt wireless camera system, which allows him to drive it around from the comfort of his home, while watching the video stream on his PC. The robot also has the ability to roam around autonomously, avoiding objects using a ping sensor that can be mounted where the camera is currently located. It seems all that’s missing is Steve Guttenberg.

As you can see in the videos below, the robot manages pretty well on all sorts of surfaces, and even walks this guy’s dogs.

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What Development Board to Use? (Part Two)

We asked for responses to our last Development Board post, and you all followed through. We got comments, forum posts, and emails filled with your opinions. Like last time, there is no way we could cover every board, so here are a few more that seemed to be popular crowd choices. Feel free to keep sending us your favorite boards, we may end up featuring them at a later date!

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The plant whisperer

[Jeff], fully acknowledging his inability to keep plants alive, has designed a system to help him out a little bit. The “Plant Whisperer” monitors water levels and notifies him if the plant needs attention. Actually, it notifies him either way. The plant whisperer uses real time text to speech to say one of several pre-programmed things, either proclaiming its happiness or requesting more water. He’s using a parallax propeller for the job as he says it is capable of handling the real time text to speech. We realize this is overkill, but we absolutely love it. The only improvement we would want would be to possibly use a pre-recorded voice for more clarity.  You can see a video of it in action after the break.

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Conways’ wall of life and whiteboard emporium

White board beats chalk board, LED marquee beats white board, and an LED white board trumps them all.

This hybrid lets you draw on the surface with dry erase markers while Conway’s game of life plays out underneath. [Bert] sent us this tip after seeing yesterday’s office marquee. This version is quite similar in appearance but the guts are very different. Inside you’ll find a Parallax SX28 microcontroller doing the heavy lifting. The display is multiplexed but they didn’t go with a common 595 shift register, but a beefier MAX6979 LED driver. We’re not too familiar with this part but it does have a lot of nice features like constant current, and automatic shutdown if serial data stalls for more than 1 second. This is a low-side driver so transistors are used to connect voltage to the rows; the opposite from the setup we looked at yesterday. This was built several years ago and is still working happily even though its permanent home is a breadboard. Source code can be found on this page.

Keyless entry via SMS

[Billy's] work got new keys which he didn’t want to carry around with him. Instead he built this system to unlock the door via text message. It is based around a Spinneret Web Server which drives a servo motor. He’s rigged up a pipe hanger to add some leverage to the lock’s knob. We’re surprised that the servo has enough power to do the job here but the video after the break shows there’s really no problem. On the communication side of things [Billy] set up Twilio to wait for text messages from an approved list of senders, then used an HTML form to issue the unlock commands to the webserver.

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