Knockoff Kapton Nearly Sinks DIY Flex PCB Project

[TinkersProjects] experimented with making their own flexible PCB for LED modules inside a special fixture, and the end result was at least serviceable despite some problems. It does seem as though the issues can be at least partially blamed on some knockoff Kapton tape, which is what [TinkersProjects] used as a backing material.

Incomplete etching on this DIY flexible PCB, but still salvageable.

The approach was simple: after buying some copper foil and wide Kapton tape, simply stick the foil onto the tape and use the toner transfer method to get a PCB pattern onto the copper. From there, the copper gets etched away in a chemical bath and the process is pretty much like any other DIY PCB. However, this is also where things started to go wonky.

Etching was going well, until [TinkersProjects] noticed that the copper was lifting away from the Kapton tape. Aborting the etching process left a messy board, but it was salvageable. But another problem was discovered during soldering, as the Kapton tape layer deformed from the heat, as if it were a piece of heat shrink. This really shouldn’t happen, and [TinkersProjects] began to suspect that the “Kapton” tape was a knockoff. Switching to known-good tape was an improvement, but the adhesive left a bit to be desired because traces could lift easily. Still, in the end the DIY flexible PCB worked, though the process had mixed results at best.

Flexible PCBs have been the backbone of nifty projects like this self-actuating PoV display, so it’s no surprise that a variety of DIY PCB methods are getting applied to it.

Microstepping A PCB Motor

Over the last 2 years [Carl Bujega] has made a name for himself with his PCB motor designs. His latest adventure is to turn it into a stepper motor by adding position control with microstepping.

The NEMA stepper motors most of us know are synchronous stepper motors, while [Carl]’s design is a permanent magnet design. It uses four coils on the stator, and two permanent magnets on the rotor/dial. By varying the current through each of the four poles with a stepper driver (microstepping), the position of the rotor should theoretically be controllable with good resolution. Unfortunately, this was easier said than done. He achieved position control, but it kept skipping steps in certain positions.

The motor and controller consist of a single flexible PCB, to reduce the layer spacing and increase the coils’ magnetic field strength. However, this created other problems, since the motor shaft didn’t have a solid mounting point, and the PCB flexed as the stator coils were energized. Soldering the controller was also a problem, as the through-hole headers ripped out easily and the PCB bulged while reflowing on a hot plate, in one case even popping off components. [Carl] eventually mounted one of the PCB motors inside a 3D printed frame to rigidly constrain all the motor components, but it still suffered from missed steps. Any suggestions for fixing the problem? Drop them in the comments below.

Like his other PCB motors, the torque is very low, but should be suitable for gauges or clocks. A PCB clock with an integrated motor would be pretty cool to have on the workshop wall.

The TMC2300 stepper driver [Carl] used belongs to the same family of drivers that enable silent stepping for 3D printers. We’ve covered a few of [Carl]’s PCB actuator adventures, from his original design to linear actuators and a flexible POV display.

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Hinge Brings New Meaning To Flexible PCB

It is not a secret that flexible PC boards can bend. But despite the substrate’s flexibility, you can’t really fold them completely over. That bothered [Carl] so he developed a hinge design so that he can fold a board completely in half. You can watch a video showing an example, FlexBox, below.

Normal boards can fold over, but the copper traces can’t tolerate a very tight bend radius. [Carl’s] trick is to make the folding part have no traces at all. Only a small bridge carries traces between the two halves and it is allowed to bend almost like an interconnecting cable.

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Magnets Turn Flexible PCB Into Electric Grasshopper

Just because something doesn’t seem to have an apparent purpose, that doesn’t mean we shouldn’t try making it anyway. As flexible PCBs become cheaper and easier to order from low-scale fab houses, we’re seeing hobbyists experiment with new uses for them such as [Carl Bugeja]’s jumping circuit.

The circuit is based a coil printed on the flexible PCB itself acting as an electromagnet, but unlike other designs which use the same trick, in this one the coil is made to be the static side of an actuator. Attached to the circuit with folding arms is a stack of two permanent magnets, which work as the moving part. Since the magnets make up most of the mass of the circuit, as they’re pushed down and sprung back up, it causes the whole thing to leap around just under one centimeter off the table like a little electric grasshopper.

This is far from [Carl]’s first appearance here on Hackaday, and he’s been clearly busy exploring new uses for flexible PCBs with their properties as electromagnets, from making POV displays with them to small robots that move around through vibration. We’re excited to see what else he can come up with, and you can see this one in action after the break.

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Latest FlexLED Milestone Refines The POV Display

With his FlexLED project, [Carl Bugeja] is trying to perfect a simple and affordable persistence of vision (POV) display capable of generating “holographic” characters in mid-air. Traditionally POV systems spin LEDs rapidly to create the desired illusion, but that means motors, slip rings, and noise. As the name implies, the goal with this project is to do away with all that and replace it with a self-actuating flexible PCB.

The device is able to quickly move the LEDs back and forth quietly and efficiently thanks to a permanent magnet and magnetic coils integrated into the flexible PCB. With no motors or gears, the whole unit is smaller and less complex than other POV displays. As an added bonus, there’s no danger to the operator or the device should a curious user stick their finger into it.

The last time we took a look at this project, [Carl] had entered an earlier single-LED version into the 2019 Hackaday Prize. Competition was tough last year, and unfortunately FlexLED didn’t get selected as a Finalist. But we’re still extremely interested in seeing the project develop, and we imagine so are you.

The recently completed second version of the display features an improved coil design, eight RGB LEDs and a 3D printed base with integrated magnet. With more LEDs onboard, a single display is able to show multiple characters and even rudimentary animations. A large array of these flapping elements promises to be quite a sight.

But before you get too excited, [Carl] does have some bad news. For one, the cost of building them in small quantities is high, which is always tough for a single hacker trying to iterate a design. Worse, some of the LEDs seem to have died on this prototype already. He says it likely has something to do with the stress of flexing back and forth so quickly, which is obviously a bit troubling. He’s looking to get some feedback from the community, and is hoping to address these issues in the next version.

For an interesting look into his flexible PCB actuator projects, check out the interview [Carl] did with us at the 2018 Hackaday Superconference.

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Detecting Water Before It’s Too Late

[mcu_nerd] is like any engineer, which is why his problem of an occasionally leaky water heater sure looks like a research project with no end in sight. Sure there’s probably a commercial product out there that can be had for half the cost and a few clicks of the mouse, but what’s the point in actually solving the problem?

His log starts with research into detecting low battery voltages. Then it was a quick exploration in designing low-power circuits. When the Flexible PCB contest came along, he realized that there was a chance to design a better electrode, and he ended up winning one of the vouchers; which is where he’s at now.

It’s definitely a work in progress, and if anything it’s just a quick five minute read and an opportunity to commiserate with another wayward soul. We do like his clever use of a tealite candle tin as both the second electrode and case for his water detection circuit. There are also some KiCad files and code.

Tiny Two-Legged PCB Robot

YouTuber and electronics engineer [Carl Bugeja] has a knack for finding creative uses for flexible PCBs. For the past year, he has been experimenting with PCB motors, using them on drones, robot fish, and most recently swarm robots. This is his final video in the vibro-bot series, and he’s got his best results to date. (Embedded below.)

He started off with flexible PCB actuators as robotic legs and magnets fitted into 3D-printed shells. The flexible PCB actuators work as inefficient electromagnets, efficient enough to react to a magnet when a current runs through, but not so efficient that they don’t release immediately.

The most recent design uses a rigid 0.6 mm FR4 PCB that acts as the frame to prevent the middle of the robot from bending. The “brain” of the robot is located at its center, which is connected to the flexible PCB actuators. Since the biggest constraint on his past robots was weight, he removed two of the legs to reduce the weight by 20%, resulting in straighter walks. He also added a Bluetooth module to wirelessly control the robot and replaced his old LiPo with a new, lighter battery (28 mAh, 15 C, 420 mA).

His latest video now shows that the robot is able to move forwards, backwards, and side to side. That’s a huge improvement over his previous attempts, which mostly resulted in the robot vibrating in place or flopping around his workbench. It’s not going to fetch you a beer, but it’s really cool.

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