Parts

685 Articles

From The MacGyver Files: Using A Stepper Motor As An Encoder

April 8, 2020 by 27 Comments

It isn’t hard to imagine a scenario where you are stuck at home all day with nothing to do and certain items are in short supply. Sure, bathroom tissue gets all the press, but try buying some flour or a freezer and see how far you get. Plus online shopping has given up on next day delivery for the duration. Not hard to imagine at all. Now suppose your latest self-quarantine project needs a rotary shaft encoder. Not having one, what do you do? If you are [Tech Build] you go all MacGyver on an old printer and pull out a stepper motor.

How does a stepper motor turn into an encoder? Well, that’s the MacGyver part. We are not big fans of the physical circuit diagrams, but it looks like [Tech Build] borrowed (with credit) from an earlier post and that one has a proper schematic.

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Turn Off Those Batteries With Their Protection Chip

April 5, 2020 by 24 Comments

It should be a feature of every device powered by a lithium-ion battery, that it has a protection chip on board that automatically disconnects it should it go out of its safe voltage range. A chip most often used for this purpose in single-cell applications is the Fortune Semiconductor DW01, and [Oliver] shares a tip for using this chip to power down the battery. The DW01 has a CS, or current sense pin, which if taken high momentarily will put the chip into an off state until the battery is disconnected.

Looking at the DW01 datasheet we can see that this would work, but we can’t help having a few questions. The CS pin is a safety sensor pin, providing over current, short circuit, and reverse polarity detection. It’s the kind of pin one might mess with only when one is absolutely certain it’s not likely to trigger a dangerous fault condition, so a bit of care should be required. However, we can see that leaving its resistor in place and supplying it a momentary logic level through another resistor should work. We’d be interested in the views of any readers with more experience in the world of lithium battery protection on this hack.

Meanwhile, a good read for any reader should be our look last year at lithium-ion safety.

An Adapter To Solve Your ESP-01 Breadboard Woes

April 4, 2020 by 9 Comments

The ESP-01 launched the ESP8266 revolution back in 2014, and while today you’re far more likely to see somebody use a later version of the chip in a Wemos or NodeMCU development board, there are still tasks the original chip is well suited for. Unfortunately, they can be tricky to use while prototyping because they aren’t very breadboard friendly, but this adapter developed by [Miguel Reis] can help.

Of course, the main issue is the somewhat unusual pinout of the ESP-01. Since it was designed as a daughter board to plug into another device, the header is too tight to fit into a breadboard. The adapter that [Miguel] has come up with widens that up to the point you can put it down the centerline of your breadboard and have plenty of real estate around it.

The second issue is that the ESP-01 is a 3.3 V device, which can be annoying if everything else in the circuit is running on 5 V. To get around this, the adapter includes an SPX3819 regulator and enough capacitors that the somewhat temperamental chip gets the steady low-voltage supply it needs to be happy.

[Miguel] has released the schematics and board files so you can spin up your own copy of the adapter, but they’re also available for around $3 USD from his Tindie store.

Using A Vending Machine Bill Acceptor With Arduino

March 31, 2020 by 9 Comments

We’ve all seen, and occasionally wrestled with, bill acceptors like the one [Another Maker] recently liberated from an arcade machine. But have you ever had one apart to see how it works? If not, the video after the break is an interesting peak into how this ubiquitous piece of hardware tells the difference between a real bill and a piece of paper.

But [Another Maker] goes a bit farther than just showing the internals of the device. He also went through the trouble of figuring out how to talk to it with an Arduino, which makes all sorts of money-grabbing projects possible. Even if collecting paper money isn’t your kind of thing, it’s still interesting to see how this gadget works on a hardware and software level.

As explained in the video, a set of belts are used to pull the bill past an array of IR LEDs. The hardware uses these to scan the bill and perform some dark magic to determine if it’s a genuine piece of currency. [Another Maker] notes that these readers actually need to receive occasional firmware updates to take into account new bill designs. In fact, the particular unit he has is so out of date that it won’t accept modern $5 bills; which may explain how he got it for free in the first place.

Years ago we saw one of these bill acceptors used to make a DIY Bitcoin ATM. Of course back then, a few bucks would get you a semi-reasonable amount of BTC. These days you would skip the paper currency and do it all digitally.

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A Practical Look At Chokes For EMI Control

March 15, 2020 by 6 Comments

Radio frequency electronics can seem like a black art even to those who intentionally delve into the field. But woe betide the poor soul who only incidentally has to deal with it, such as when seeking to minimize electromagnetic interference. This primer on how RF chokes work to reduce EMI is a great way to get explain the theory from a practical, results-oriented standpoint.

As a hobby machinist and builder of machine tools, [James Clough] has come across plenty of cases where EMI has reared its ugly head. Variable frequency drives are one place where EMI can cause problems, and chokes on the motor phase outputs are generally prescribed. He used an expensive choke marketed as specific for VFD applications on one of his machines, but wondered if a cheap ferrite core would do the job just as well, and set to find out.

A sweep of some ferrite cores with a borrowed vector network analyzer proved unsatisfying, so [James] set up a simple experiment with a function generator and an oscilloscope. His demo shows how the impedance of a choke increases with the frequency of the test signal, which is exactly the behavior that you’d want in a VFD – pass the relatively low-frequency phase signals while blocking the high-frequency EMI. For good measure, he throws a capacitor in parallel to the choke and shows how much better a low-pass filter that makes.

We love demos like this that don’t just scratch an intellectual itch but also have a practical goal. [James] not only showed that (at least in some cases) a $13 ferrite can do the same job as a $130 VFD choke, but he showed how they work. It’s basic stuff, but it’s what you need to know to move on to more advanced RF filter designs.

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3D Printed Swirl Rocket Injector Turns Up The Heat

March 11, 2020 by 14 Comments

Conceptually speaking, a liquid propellant rocket engine is actually a very simple piece of hardware. All you need to do is spray your fuel and oxidizer into the combustion chamber at the proper ratio, add a spark, and with a carefully designed nozzle you’re off to the races. Or the Moon, as the case may be. It’s just that doing it in the real-world and keeping the whole thing from exploding for long enough to do some useful work is another story entirely.

Taking the process one step at a time, [Luke Walters] has been working on a 3D printed injector that tackles the first half of the problem. After nearly a dozen different prototypes, he’s come up with a printable injector design that atomizes the fuel and combines it with pressurized air at a suitable ratio for combustion. As you can see in the video at the break, it’s certainly capable of generating some impressive fireballs.

A cloud of highly atomized alcohol from the injector.

The internal passages of the injector have been designed in such a way that fuel (91% isopropyl alcohol) and air are spinning in opposite directions when they meet. This promotes more complete mixing, which in turn leads to a more efficient burn. Originally developed in the 1930s, so-called “swirl injectors” of this type were one of the key technological advancements made by Germany’s V-2 rocket program. Some ideas never go out of style.

Since the injector only touches the fuel and air prior to ignition, it doesn’t need to be particularly heat resistant. To be on the safe side [Luke] has printed the part in PETG at 100% infill, but in reality the flame front is far enough away that temperature isn’t much of a concern. That said, he does hope to eventually fit these injectors into some kind of combustion chamber, which is where things will start getting toasty.

To be clear this is not a rocket engine, and it produces no appreciable thrust. Turning a big flame into a useful means of propulsion is where things get tricky, almost as though it’s rocket science or something. But that doesn’t mean it can’t be done by suitably ambitious hackers.

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Forming Sheet Metal Parts With 3D Printed Dies

March 10, 2020 by 27 Comments

Using 3D printed forms to bend sheet metal isn’t exactly new. We’ve seen several people create custom dies for their brakes, and the results have shown the concept has merit for small-scale production. But that’s usually where the process ends. A bend here or there is one thing, but the ability to form a complex shape with them has always seemed like asking too much. But judging by his recent experiments, [Shane Wighton] is very close to changing that perception.

The process at work here is, relatively speaking, pretty simple. You print out the upper and lower die, put a piece of sheet metal between them, and then smash them together with a hydraulic press. If everything works correctly, and your CAD skills hold true, the metal will take the desired shape.

Of course, that’s vastly oversimplifying things. As [Shane] explains in the video after the break, there are many nuances to forming sheet metal like this that need to be taken into account, and iteration and experimentation are basically unavoidable. So it’s a good thing you can rapidly redesign and reprint the dies.

Which isn’t to say that the dies themselves didn’t come with their own unique set of challenges. The first ones shattered under the pressure, and it took a few design revisions and eventually a switch to a stronger resin before [Shane] got a set of dies that could form the desired piece. Even still, he’s had a lot of trouble getting the printed parts to survive multiple uses. But he’s confident with some more refinements he could get a repeatable process going, and thinks ultimately producing runs of up to 100 parts on a set of printed dies isn’t out of the question.

Logically, it would seem plastic isn’t an ideal choice for punching and shaping metal. Frankly, it’s not. But if you’re doing in-house manufacturing, the ability to produce complex tooling quickly and easily can help make up for any downsides it might have.

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