"Je t'aime," "Ti amo," or "I love you," there are many ways to express feelings of love towards your special someone.
With Valentine's Day still lingering in our storefronts and discount racks, Carl Bugeja recently challenged himself to find his own unique way of letting his partner know just how much she means to him.
While many of us might try some PCB art, or some simple circuit sculpture, Bugeja has built on the success of his flex PCB motor work, and created a really nifty kinietic LED POV (persistence of vision) display, capable of drawing pixellated graphics like this lovely heart shown above.
For those who haven't seen Bugeja's work before, it's fair to say that he has an affinity for flexible PCB actuators. Having become a dab hand at laying out densely packed, intricate coils onto flexible PCB substrate, he is able to create actuators that deflect against a Neodynium magnet, when current is applied to the coil. FlexLED first came across my browser window over here for his first prototypes.
Now, Bugeja is back with FlexLED 2.0, and it's an wonderfully excecuted idea of engineering ingineuity!
In a nutshell, FlexLED is a new take on a POV display. If you apply a periodic signal of the right amplitude to the coils, they can be made to flex rapidly within a set angle of deflection.
Those of us who have played with POV toys (desk clocks, or even fidget spinners) will recognize a suitable physical platform for moving LEDs quickly enough to create a POV display, even if it is oscillating rather than rotary, it's still moving quickly enough in a repeating fashion to function very well in this role!
FlexLED is more than just a set of flexible coils and passive LEDs, however. Bugeja has designed and assembled a hybrid PCB assembly, with flexible polyamide coils and a solid FR4 "driver board," incorporating a Texas Instruments TLC6C5724, which takes care of driving the side-firing, an eight RGB SMT LED array, located along the edge of the flexible coil assembly.
To relieve the host electronics from having to devote timers and I/O to driving the coils with the appropriate switching waveforms, a PIC16F15324T takes care of delivering the animation bitstream to the LED driver, and communicating with the outside world over a UART interface.
While the onboard PIC takes care of the timing and I/O sequencing to drive the coils, the limited current capability of the PIC's I/O drivers isn't enough to drive the required amount of current to move the coils against the magnetic field of the Neodynium magnets.
To make sure enough current is passed through the coils, a DRV8837 half-bridge is used.
A simple H-bridge is more commonly found when implementing direction control on a DC motor, though they are usually found in one form or another when you are tasked with controlling bi-directional current flow, through a load.
If we consider the mapping of the DRV8837 inputs to the switch numbers in the above diagram, the function of the coil driving circuit becomes clearer. With switches 1 and 4 effectively mapped to OUT1, and switches 2 and 3 effectively mapped to OUT2, we can imagine the flexible PCB coil in place of the coil shown in the above diagram.
With current flowing in one direction, a magnetic feild is generate to oppose the field of the magnets. Switch the flow of current, and now the flexible coil is attracted to the magnet. Repeat the process quickly enough, and the coil with oscillate in motion, providing the rapid movement needed to generate the POV effect. Clever!
The thought and planning that goes into Bugeja's work always shows through in the level of integration present in the final product. FlexLED is no exception, and even when not functioning, the hybrid PCB assy alone are a work of art.
When I first saw the photo above, I was mistaken in thinking Bugeja has chosen to showcase the fabrication capabilities of OSHPark, with both their flex and After Dark services. Alas, I was mistaken!
While many of us would have been satisfied with a two-part assembly, fusint the flexible coil FPC to a solid FR4 board, Bugeja has taken the idea to the next level of manufacture, by designing a hybrid flex/FR4 PCB for the manufacturer to assemble.
Usually the domain of wearable electronics, or high-end kit, Rigid-flex, as it is known, can really ratchet up the cost of a design, with so much additional complexity to account for in comparison to working with "plain" FR4, or even soley flex polyamide designs.
From the hybrid PCB stackup, to the rounded corners present on the Flex itself, it is quite clear that Bugeja knows exactly what he's up to. A careful review of his work can provide some well proven tips and tricks for wokring with these advanced tehniques!
Maybe with the slight oversight of some untented vias, but we've all been there! A little bit of ENIG gold doesn't look too bad, and at least they are thermal ground relief, and not much more of an issue than the plated mounting holes.
We should all be so lucky to be the recipient of such fine work, and the smile shown below by Bugeja's partner certainly shows appreciation of the thought behind, and the work itself.
You can support Bugeja on Patreon to help him develop more cool ideas, but if you need a little incentive / preview first, he has released a full video on FlexLED!