Making a Power Inductor Checker

inductor-checker-for-oscilloscope

Back to the basics: there are three kinds of passive electronic components: Inductors, Capacitors and Resistors. An inductor can be easily built and many types of core and bobbin kits are available. However, characterizing one hypothetical coil you just made is quite tricky as its inductance will depend on the measurement frequency and DC bias current. That’s why [ChaN] designed the circuit shown above.

As you may guess, RF enthusiasts are more interested in the inductance vs frequency curve while power circuit designers prefer inductance vs load current (for a given frequency). The basic principle behind the circuit shown above is to load an inductor for repetitive short periods and visualizing the current curve with an oscilloscope connected to a sense resistor. When loading the inductor, the current curve will be composed of two consecutive slopes as at a given moment the coil’s core will be saturated. Measuring the slope coefficient then allows us to compute the corresponding inductance.

[Via Dangerous Prototypes]

Fail of the Week: Flaming Brushless Motor Controller

fotw-flaming-brushless-motor-controller

Yep, smoke and flames are usually a sign that your electronics aren’t functioning as expected. This is actually the second failure encountered while learning about brushless motor controllers.

[Michael Kohn] purchase the motor while working on a different project and it went unused for quite some time. When he came across it again he decided he should learn the not-so-dark art of BLDC control.

The first hurdle was to figure out how to drive the three-wire motor when he had been expecting only two. The answer required him to come up with switching mechanism that allows three states for each wire: positive, negative, and not connected. His solution was to use MOSFETs. It’s a good idea, but unfortunately during the first iteration they were under-spec’d and he scared the crap out of himself when one of them blew up during testing (clip #1 below). After sourcing a more robust set of MOSFETs [Micheal] went back to testing which is when this little fire broke out. The 22 gauge wires connecting the Lithium battery to the driver just couldn’t cut it. See for yourself in the second clip.

It’s been awhile since we’ve said it: Please remember the Fail of the Week is not about ridiculing the hacker who was gracious enough to document his or her failure. It’s about learning from the mistake and discussing alternatives that can help others in the future. For instance, in this case some advice in determining MOSFET specs and wire gauge for any type of motor would be quite helpful. Have at it in the comments.

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Interactive Boozeshelf is its own Dance Party

boozeshelf

[Jeremy] refused to settle on your typical alcohol storage options, and instead created the Boozeshelf. Like most furniture hacks, the Boozeshelf began as a basic IKEA product, which [Jeremy] modified by cutting strips of wood to serve as wine glass holders and affixing the front end of a wine rack at the base to store bottles.

In its standard operating mode the Boozeshelf lies dark and dormant. Approaching it triggers a cleverly recessed ultrasonic sensor that gently illuminates some LEDs, revealing the shelf’s contents. When you walk away, then lights fade out. An Arduino Mega running [Jeremy's] custom LEDFader library drives the RGB LED strips, which he wired with some power MOSFETS to handle current demands.

[Jeremy] didn’t stop there, however, adding an additional IR receiver that allows him to select from three different RGB LED color modes: simple crossfading, individual shelf colors (saved to the on-board EEPROM), or the festive favorite: “Dance Party Mode.” Stick around after the break to see [Jeremy] in full aficionado attire demonstrating his Boozeshelf in a couple of videos. Considering blackouts are a likely result of enjoying this hack, we recommend these LED ice cubes for your safety.

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The easy or hard way to build a PWM dimmer

555

From what you would gather from Hackaday’s immense library of builds and projects over several years, the only way to do PWM is with a microcontroller, some code, a full-blown IDE, or even a real-time operating system. To some readers, we’re sure, this comes naturally and with an awesome toolchain it can be as easy as screwing in a light bulb. There is, of course, an easier way.

[Jestin] needed to vary the current on a small 12 Volt load. Instead of digging out an in system programmer, he turned to the classic 555 chip. With a single pot, it’s easy to vary the duty cycle of the 555 and connect that to a MOSFET. Put a load in there, and you have a very easy circuit that’s a fully functioning PWM dimmer.

If all you have are a few scraps in your part drawers, this is a very, very easy way to set up a dimmer switch. We’re also loving [Jestin]‘s improv aluminum tube enclosure, as seen in the video below.

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A real car remote controlled with an Arduino… what could go wrong?

[Gilad] tipped us about his latest project, where he adds plenty of pneumatics and electronics into his wife’s car to remote control it.

The brake/throttle pedals are actuated by pistons controlled by electronic valves, and a standard DC motor is in charge of turning the wheel. The Arduino code tells us that the valves will be opened as long as the remote up/down channel is above/under given values. The frame is based on Festo aluminium profiles and we’re not sure where the mains used for the DC/DC converters is coming from.  As the valves use 24V and the motor 12V, standard N-Mosfets and power relays are used for voltage conversion. The remote controller [Gilard] used is actually 20 years old, so the output signal of the receiver isn’t actually really clean.

We do hope to never see this car on the road….

Build a light following bristlebot as a way to teach science

light-following-bristlebot

[Ben Finio] designed this project as a way to get kids interested in learning about science and engineering. Is it bad that we just want to build one of our own? It’s a light following bristlebot which in itself is quite simple to build and understand. We think the platform has a lot of potential for leading to other things, like learning about microcontrollers and wireless modules to give it wireless control.

Right now it’s basically two bristlebots combined into one package. The screen capture seen above makes it hard to pick out the two toothbrush heads on either side of a battery pack. The chassis of the build is a blue mini-breadboard. The circuit that makes it follow light is the definition of simple. [Ben] uses two MOSFETs to control two vibration motors mounted on the rear corners of the chassis. The gate of each MOSFET is driven by a voltage divider which includes a photoresistor. When light on one is brighter than the other it causes the bot to turn towards to the brighter sensor. When viewing the project log above make sure to click on the tabs to see all of the available info.

This directional control seems quite good. We’ve also seen other versions which shift the weight of the bot to change direction.

[Read more...]

Brilliant auto-off feature for a bike light

auto-off-bike-light-switch

If you’re going to use your bicycle as transportation at night you really must have a head and tail light in hopes that the crazy drivers don’t hit you. For good reason, these lights don’t turn themselves off. But [Miceuz] kept forgetting to shut it down upon arrival and always ended up with dead batteries. His quest for an auto-off feature that actually worked ended in a brilliant and simple add-on circuit.

He first thought about using an accelerometer, but couldn’t find one that fit the bill without also adding a microcontroller. He came up with an even simpler circuit, which can be seen at the base of the black plastic housing. It’s a bit of copper clad board with a small spring attached. The spring completes an RC timer circuit which drives a MOSFET. When that circuit is charged, the MOSFET connects power to the bike light. When the cap runs out the MOSFET threshold cuts power and everything turns off. Since the spring jiggles while he rides it provides the momentary connection necessary to charge the capacitor. Stay stationary for about 30 seconds and the auto-off kicks in.