Function Generator with Zero CPU Cycles


No one is sitting around their workbench trying to come up with the next great oscilloscope or multimeter, but function generators still remain one of the pieces of test equipment anyone – even someone with an Arduino starter pack – can build at home. Most of these function generators aren’t very good; you’re lucky if you can get a sine wave above the audio spectrum. [Bruce Land] had the idea to play around with DMA channels on a PIC32 and ended up with a function generator that uses zero CPU cycles. It’s perfect for a homebrew function generator build, or even a very cool audio synthesizer.

The main obstacles to generating a good sine wave at high frequencies are a high sample rate and an accurate DAC. For homebrew function generators, it’s usually the sample rate that’s terrible; it’s hard pushing bits out a port that fast. By using the DMA channel on a PIC32, [Bruce] can shove arbitrary waveforms out of the chip without using any CPU cycles. By writing a sine wave, or any other wave for that matter, to memory, the PIC32 will just spit them out and leave the CPU to do more important work.

[Bruce] was able to generate a great-looking sine wave up to 200 kHz, and the highest amplitude of the harmonics was about 40db below the fundamental up to 100 kHz. That’s a spectacular sine wave, and the perfect basis for a DIY function generator build.

Baby Quadruped Robot, Learning To Walk

Cheap Quadruped Robot

We’ve all seen videos of those crazy Boston Dynamics running quadruped robots that can reach up to 28 mph. Those things are amazing and it’s almost impossible to imagine how to even start building one. [Max] loves his robots and wanted to build a quadruped but, being a robot hobbyist, didn’t have the serious cash needed to make an extravagant robot like those of Boston Dynamics. Instead he started bridging the gap by designing a quadruped robot that is a little bit slower and tons cheaper.

quadruped-joint[Max] designed all of the mechanical parts himself. After weighing the advantages and disadvantages of different materials, he decided that the frame would be made from 5mm acrylic sheet. The main body of the robot has acrylic ribs that are spaced apart by threaded rods. Twelve RC servos make up all of the joints, 3 in each leg. Notice in this photo how there is one servo that immediately rotates another servo. To support the other side of the rotating servo, [Max] epoxied on a T-nut, stuck in a short length of threaded rod which is then supported in the frame by a ball bearing. Simple and effective! The upper portions of the legs are also made from acrylic sheet and the lower legs are from a cheap camera tripod. Rubber feet ensure a slip resistant stance.

All of the servos are controlled by an Arduino Mega. [Max] is currently writing a sketch that will perform the complex math and determine coordinated servo motions for movements us humans take for granted, like ‘walk forward’. As you can see in the videos, [Max's] robot won’t be catching the Boston Dynamics’ Cheetah any time soon but he is off to a great start.

Future plans for this project include bluetooth control and integrating the ultrasonic sensor proactively installed in the ‘head’ of the robot. Check out the videos after the break. [Max] is looking for some feedback on his project. We here at HaD think this needs a great name. Let’s hear some suggestions in the comments…

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Cassette Tape Hack Turns Scratching into Sliding


It’s common to see a DJ use a turntable as a musical instrument. Physically manipulating a record while its playing produces its own unique sound, but it takes some finesse and puts strain on the delicate workings of the player when you do it. With this in mind, [Jeremy Bell] has refreshed the notion of appropriating old technology to create new sound with his home-brewed scrubboard.

Making use of a cassette tape, [Jeremy] dissected samples from the reel and laid them out in horizontal strips over rails to hold their form. The pickup from the tape player has been hacked into a separate piece that glides smoothly over these rails, giving the user the ease of control. To produce the immediate cutting effect that is less easy to perform with his device than a record player, [Jeremy] created an on and off switch which is simply a close pin covered in foil that teeters over a metal contact (in this case a coin). The end product sounds exactly like scratching a record, but better because he’s doing it with hacker showmanship. One can only image the awesome potential for more elaborate setups having multiple tape samples and the like!

There are a few different videos of the scrubboard in use on [Jeremy’s] website. He is also running a Kickstarter right now in order to turn the project into a stand alone instrument with improved features.

Thanks Omar, for telling us about this cool re-envisionment!

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Ceci N’est Pas Une Clock


[Justin] tipped us about his slick custom OBD-II gauge that could easily pass for an OEM module. He was able to use the clock area of his Subaru BRZ to display a bunch of information including the oil and coolant temperatures and the battery voltage.

The forum post linked above has a good FAQ-based explanation of what he did, but so many people have told him to shut up and take their money that he created an Instructable for it. Basically, he’s got a Sparkfun OBD-II UART board communicating with a pro Trinket. The display is an Adafruit OLED, which he found to be an ideal choice for all the various and sundry light conditions inside the average car.

[Justin] was able to reuse the (H)our and (M)inute buttons and reassigned them to (H)igh to show the peak reading and (M)ode to, well, switch between modes. The (:00) now resets the peak readings. He offers suggestions for acquiring the specific CAN codes for your car to make the data more meaningful. [Justin]‘s code is safe in the many tentacles of Octocat, and you can check out his demo video below.

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Digital Data from a Cheap Power Meter

Cheap Power Meter

Power meters like the Kill-A-Watt are great for keeping track of energy usage, and are also very hackable. The Kill-a-Watt in particular puts out analog signals proportional to current and voltage, which makes it easy to interface with a microcontroller.

Although reading analog voltages is easy enough, [Kalle] found a cheap Chinese power meter that is even more hackable. These inexpensive power meters cost about the same as a first-generation Kill-a-Watt, but they directly stream out digital data. The power meter [Kalle] hacked has a non-US plug, but the meter is available from the usual suppliers (eBay, Aliexpress, etc) with a 3-prong US plug and 120v rating.

After breaking out a logic analyzer, [Kalle] discovered that the meter constantly streams voltage, current, and power data from the measurement board to the display board on a SPI-like bus. The ribbon cable inside the meter even has the clock and data bus lines clearly labelled. [Kalle] went on to reverse-engineer the protocol and write an Arduino sketch that parses the stream, making it even easier to integrate this meter into your next power monitoring project.

Take Your Samples for a Spin with the RWXBioFuge

RWXBioFuge collage v0.1We have a confession to make: we love centrifuges. We’ve used all shapes and sizes, for spinning bags of whole blood into separate components to extracting DNA, and everything in between. Unfortunately, these lab staples are too expensive for many DIY-biologists unless they buy them used or build them themselves. [Pieter van Boheemen] was inspired by other DIY centrifuges and decided to make his own, which he named the RWXBioFuge.

[Pieter] designed the RWXBioFuge using Sketchup, OpenSCAD, and InkScape. It features a Thermaltake SMART M850W ATX power supply, an R/C helicopter Electronic Speed Controller (ESC), and brushless outrunner motor. For user output it utilizes a 16×2 LCD character display with an I2C interface.The frame is laser-cut from 3mm MDF while the 3D-printed PLA rotor was designed with OpenSCAD.

An Arduino handles the processing side of things. [Pieter] used an Arduino Ethernet – allowing a web interface to control the centrifuge’s settings and operation from a distance. We can see this being useful in testing out the centrifuge for any rotor/motor balance issues, especially since [Pieter] states that it can be configured to run >10,000 rpm. We wouldn’t want to be in the room if pieces start flying off any centrifuge at that speed!  However, we feel that when everything’s said and done, you should have a centrifuge you can trust by your side when you’re at your lab bench.

While there are similarities to the Openfuge, the larger RWXBioFuge has rotor capacities of eight to twenty 1.5-2.0ml microcentrifuge tubes. Due to the power supply, it is not portable and a bit more expensive, but not incredibly so. There are some small touches about this centrifuge that we really like. The open lid detector is always a welcome safety feature. The “Short” button is very handy for quick 5-10 second spins.

A current version of the RWXBioFuge is being used at the Waag Society’s Open Wetlab. [Pieter's] planned upgrades for the next version include a magnetic lid lock, different rotor sizes, an accelerometer to detect an improperly balanced rotor, and optimizing the power supply, ESC, and motor setup. You can never have enough centrifuges in a lab, and we are looking forward to seeing this project’s progress!

Check out a few more pictures of the RWXBioFuge after the break.

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Retrotechtacular: Blue Collar, Red Nightmare

american dadThis week’s presentation is a well-cast piece of anti-Communist propaganda perpetrated by a division of the DoD that you’ve probably never heard of: the Directorate for Armed Forces Information and Education.

It’s narrated by Jack Webb of Dragnet and Adam-12 fame. He tells us of a fake American town located somewhere behind the Iron Curtain. It’s full of young comrades who sock hop and bebop while studying and playacting the bourgeoisie activities of the American economy and way of life. After introducing this, Webb pulls back the cushy, velvet curtain to profile a typical American household led by one [Jerry Donavan].

[Jerry] has it all: a wise-cracking wife played by Jeanne Cooper (most notably of The Young and the Restless), a son with a healthy interest in war games, a young daughter with pretty blond hair, and a beautiful older daughter who would go on to fame up the road at Petticoat Junction. After some unsettling news from this daughter at the dinner table, Jerry heads up to bed early to catch a few Zs.

Jack Webb denies [Jerry] any visions of sugar plums and instead drops him in the middle of Fakesville, USSR for a vivid nightmare of an America reconstructed by Communism. Watch as he figures out what’s going on and what the new regime means for him and his good-looking family.

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