A Very Accurate Current Probe

There’s many different ways of measuring current. If it’s DC, the easiest way is to use a shunt resistor and measure the voltage across it, and for AC you could use a current transformer. But the advent of the Hall-effect sensor has provided us a much better way of measuring currents. Hall sensors offers several advantages over shunts and CT’s – accuracy, linearity, low temperature drift, wider frequency bandwidth, and low insertion loss (burden) being some of them. On the flip side, they usually require a (dual) power supply, an amplification circuit, and the ability to be “zero adjusted” to null output voltage offsets.

[Daniel Mendes] needed to measure some fairly high currents, and borrowed a clip-on style AC-DC current probe to do some initial measurements for his project. Such clip on current probes are usually lower in accuracy and require output DC offset adjustments. To overcome these limitations, he then built himself an invasive hall sensor current probe to obtain better measurement accuracy (Google Translated from Portugese). His device can measure current up to 50 A with a bandwidth stretching from DC to 200 kHz. The heart of his probe is the LAH-50P hall effect current transducer from LEM – which specialises in just such devices. The 25 mV/A signal from the transducer is buffered by an OPA188 op-amp which provides a low output impedance to allow interfacing it with an oscilloscope. The op-amp also adds a x2 gain to provide an output of 50 mV/A. The other critical part of the circuit are the high tolerance shunt resistors connected across the output of the LAH-50P transducer.

The rest of his design is what appears to be a pretty convoluted power supply section. [Daniel] wanted to power his current probe with a 5V input derived from the USB socket on his oscilloscope. This required the use of a 5 V to 24 V boost switching regulator – with two modules being used in parallel to provide the desired output power. A pair of linear regulators then drop down this voltage to +15 / -15 V required for the trasducer and op-amp. His blog post does not have the board layout, but the pictures of the PCB should be enough for someone wanting to build their own version of this current sensor.

Raspberry Pi Controlled Chicken Door

We’re not sure if the Chickens know it yet, but they could be one of the reasons for all this IoT craze now a days. Look for chicken coop, and out come dozens of posts from the Hackaday chest.

Here’s another one from self confessed lazy engineer [Eric]. He didn’t want to wake up early to let his chickens out in the morning, or walk out to the coop to lock them up for the night to protect them from predators like Foxes, Raccoons and Opossum. So he built a Raspberry-Pi controlled chicken coop door that automates locking and unlocking. The details are clear from his video which you can watch after the break. The door mechanism looks inspired from an earlier anti-Raccoon gravity assist door.

The hardware (jpg image) is simple – a couple of hall sensors that detect the open/close status of the coop door that is driven by a DC motor via a bridge controller. The whole setup is controlled using a Raspberry-Pi and this is where the fun starts – because he can now add in all kinds of “feature creep”. Motion sensor, camera, light array, and anti-predator gizmos are all on his drawing board at the moment. Add in your feature requests in the comments below and let’s see if [Eric] can build the most advanced, complicated, gizmo filled chicken coop in the Universe. Combine that with this design, and it could even turn out to be the most beautiful too.

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Rigging Your 3D Models In The Real-World

Computer animation is a task both delicate and tedious, requiring the manipulation of a computer model into a series of poses over time saved as keyframes, further refined by adjusting how the computer interpolates between each frame. You need a rig (a kind of digital skeleton) to accurately control that model, and researcher [Alec Jacobson] and his team have developed a hands-on alternative to pushing pixels around.

3D Rig with Control Curves
Control curves (the blue circles) allow for easier character manipulation.

The skeletal systems of computer animated characters consists of kinematic chains—joints that sprout from a root node out to the smallest extremity. Manipulating those joints usually requires the addition of easy-to-select control curves, which simplify the way joints rotate down the chain. Control curves do some behind-the-curtain math that allows the animator to move a character by grabbing a natural end-node, such as a hand or a foot. Lifting a character’s foot to place it on chair requires manipulating one control curve: grab foot control, move foot. Without these curves, an animator’s work is usually tripled: she has to first rotate the joint where the leg meets the hip, sticking the leg straight out, then rotate the knee back down, then rotate the ankle. A nightmare.

[Alec] and his team’s unique alternative is a system of interchangeable, 3D-printed mechanical pieces used to drive an on-screen character. The effect is that of digital puppetry, but with an eye toward precision. Their device consists of a central controller, joints, splitters, extensions, and endcaps. Joints connected to the controller appear in the 3D environment in real-time as they are assembled, and differences between the real-world rig and the model’s proportions can be adjusted in the software or through plastic extension pieces.

The plastic joints spin in all 3 directions (X,Y,Z), and record measurements via embedded Hall sensors and permanent magnets. Check out the accompanying article here (PDF) for specifics on the articulation device, then hang around after the break for a demonstration video.

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Interactive dice game pits man against machine


While most dice games are based on luck and chance more than anything else, [Mike] decided he wanted to create a dice game that took a little more skill to play. He built a replica of a game found in Ian Stewart’s “The Cow Maze”, a book of mathematical stories and puzzles.

The theory behind the game is as follows:

A number is randomly drawn and is considered the “heap”. Players take turns reducing the heap, using the die to represent the number they would like to remove. The only restrictions placed on moves are that you cannot re-use the same number chosen by your opponent in the preceding move, nor can you use the number on the die face opposite that number. The winner of the game is the individual reducing the heap to exactly zero, though you can also lose the game automatically if you reduce the heap to a negative number.

The game operates using a magnet-loaded wooden die and hall sensors built into the playing surface. The sensors relay the value of the die’s face to the ATmega chip he used to run the game. His code provides the logic for your computer opponent as well as for keeping score.

The whole project is wrapped up in a nice-looking wooden box that gives it a bit of old time-y charm, micro controller and LCD aside.

Be sure to check out the video below to see a few rounds of the game being played, and swing by his site for more details.

[via SparkFun]

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