Cleaning up a Low-Cost Buck-Boost Supply

Cheap DC-DC converters have been a boon on the hobbyist bench for a while now, but they can wreak havoc with sensitive circuits if you’re not careful. The problem: noise generated by the switch-mode supply buried within them. Is there anything you can do about the noise?

As it turns out, yes there is, and [Shahriar] at The Signal Path walks us through a basic circuit to reduce noise from DC-DC converters. The module under the knife is a popular buck-boost converter with a wide input range, 0-32 VDC output at up to 5 amps, and a fancy controller with an LCD display. But putting the stock $32 supply on a scope reveals tons of harmonics across a 1 MHz band and overall ripple of about 66 mV. But a simple voltage follower built from a power op-amp and a Zener diode does a great job of reducing the spikes and halving the ripple. The circuit is just a prototype and is meant more as a proof of principle and launching point for further development, and as such it’s far from perfect. The main downside is the four-volt offset from the input voltage; there’s also a broad smear of noise at the high end of the spectrum that persists even with the circuit in place. Centered around 900 MHz as it is, we suspect a cell signal of some sort is getting in. 900 kHz.

If you haven’t checked out the videos at The Signal Path, you really should. [Shahriar] really has a knack for explaining advanced topics in RF engineering, and has a bench to die for. We’ve covered quite a few of his projects before, from salvaging a $2700 spectrum analyzer to multiplexing fiber optic transmissions.

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Lego Boosts Their Robotic Offering

Kids often have their first exposure to robots in school using Lego Mindstorm kits. Now Lego is rolling out Boost — a robotic kit targeting all Lego builders from 7 years old and up. The kit is scheduled to be on the market later this year (it appeared at the recent CES) and will sell for about $160.

[The Brothers Brick] had a chance to try the kit out at CES (see the video below) and you might find their review interesting. The kit provides parts and instructions to build five different models: a cat, a robot, a guitar, a 3D printer, and a tracked vehicle. You can check out the official page, too.

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A Buck-Boost Converter from the Ground Up

DC to DC conversion has come a long way. What was once took an electromechanical vibrator and transformer has been reduced to a PC board the size of a largish postage stamp that can be had for a couple of bucks on eBay. So why roll your own buck-boost converter for the ground up? Maybe because sometimes the best way to learn is by doing.

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Boost Around Town with This 3D Printed Bicycle Assist

[MechEngineerMike]’s bike boost is just a pleasure to look at, and, we’re certain, a relief to use. While it’s not going to rocket you down the street, it will certainly take some of the pain away. (Just like the professionals!)

It’s one thing to design a device that can fit one bicycle. It’s quite another feat if it can support multiple frames. On top of that, it’s even simple. It attaches at one point and transfers the power to the wheel easily. There’s even just one wire to connect, an RCA cable, to engage the boost.

We really like the clever way [Mike] used the rotating shell of an outrunner motor as the surface that presses against the wheel. We wonder if a cast polyurethane rubber tire for the motor would help, or just help overheat the motor?

The parts for the device are 3D printed and pretty chunky. They should hold up. Check out the video of it boosting [Mike] to the grocery store, where he can, presumably, buy less with all the calories he saved after the break.

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How to design your own LED driver

If you find yourself in need of a driver for a high power string of LEDs this is a must read. [Limpkin] just designed this driver as a contract job. He can’t show us the schematic, but he did share some tips on how to build an LED driver around a MAX16834 chip.

As you move to higher power designs the barriers to success pile up rather quickly. Using a chip like the MAX16834 really helps to simplify the task as it can be used as a boost or buck converter, it includes functionality that allows for dimming, and it’s a constant currents solution. There are board design issues that need to be accounted for in these designs. [Limkin] included links to a few calculators that will help you determine trace width based power levels used with the driver. He also recommends using copper pours on both sides of the board connected with vias to help dissipate heat. To that end he used an IR thermometer for feedback during testing.

It’s too bad he doesn’t have any photos of the device at work. If you build something similar please take some pictures and tip us off about it.

Cellphone battery booster built at the checkout counter

When you’re away from home and your cellphone runs out of juice it can be a real downer. Sure, you could find a store and buy a wall charger, but wouldn’t it be more fun to build your own battery booster without using tools? [Spiritplumber] did just that, popping into a Radio Shack for the parts, then making his how-to video (embedded after the break) while standing at the checkout counter. You can see he hust set his camera on top of the battery display case and got to work.

He’s using four D cell batteries to provide 6 volts of power. Assuming your phone charges at 5 volts this is going to be just a bit too high, even though there’s some tolerance with most phones. To overcome that obstacle he added a diode to the circuit, taking advantage of the 0.7 volt drop that it brings to the mix. Grab a plug adapter for your model and then just hand twist the connections. [Spiritplumber] admits it would be better to solder these, but in a bind you can get away with it. We looked up some prices for this method and we figure this would cost around $18 (batteries included) depending on the price of the plug adapter for your phone.

Of course if you’re just looking for a way to charge your phone without paying consumer prices there are ways of accomplishing that as well.

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Breathing motion powered USB charger

When your batteries run low you can use your body to recharge them. This contraption generates power from chest expansion while breathing. [Jmengel] used some gears from old optical drives to boost the RPM generated by a belt around your torso that he calls a thorax expansion coupler. When you breath in, that belt pulls on a plate that spins the gears, ultimately rotating a small motor. The AC current generated by that motor is run through a rectifier and a boost converter, then fed to a charging circuit.

Does it work? Not really, as this only outputs around 50 mW. But we like the twinge of Dune nostalgia we get looking at it. Wouldn’t this be a perfect addition to a stillsuit?