LED Matrix Earrings – mitxela.com

2024-02-20 14:34:12

20 Feb 2024
Progress: Full

I initially imagined the LED Industrial Piercing as a undertaking particularly to utilize 0201 LEDs. Ultimately, they weren’t even obligatory. 0201 LEDs are simply too small! Evidently, we wanted to go deeper, so the aim of this subsequent undertaking was to stay as many as potential of them onto the face of a stud earring.

Watch the next youtube video for an extensively narrated journey.

Proceed studying this web page for an in-depth rationalization.

Design

These off-the-shelf LED stud earrings are very low cost. They’ve a tiny machined battery holder for 2 LR521 cells. The concept was to exchange the plastic gemstone and single LED with our personal circuit board, re-using the metalwork.

Electrically, the circuit and firmware can be an identical to the badge I lately created utilizing a CH32V003. Learn that web page for the story behind it and a proof of the way it works.

The problem right here is shrinking the design of the badge by an element of three (or one-ninth the world) by shifting from an LED pitch of 3mm right down to 1mm. We additionally insisted on not having a thick border across the board. This poses fairly a problem for routing the tracks.

To provide a way of scale, here is three 0201 LEDs subsequent to an everyday floor mount LED:

Or, to actually put it in perspective, an 0201 LED on the again of an ATtiny85:

Homebrew blind and buried vias

It is potential to get multilayer boards made with so-called blind and/or buried vias. The restrict is way, far past what we’re working with right here. The “redistribution layer” of BGA packages is often constructed as a really small, high-density circuit board. These usually have very superb pin pitches and use blind vias, via-in-pad, and so forth. The purpose is we may simply order a circuit board to those tolerances – if we had the money for it.

A small batch of HDI boards begins at a number of hundred {dollars}, and the extra advanced the stackup the extra the worth goes up. I’d very very like to maintain this complete undertaking beneath $50 whole.

I made a decision to craft my very own circuit board sandwich, two two-layer boards held collectively by an array of solder pads.

I wasn’t positive if this was going to work. I put all of the pads round across the perimeter, partly with the concept I may examine all of the connections, after all that might imply eradicating the boards from the panel to take action, which I did not wish to do till the remainder of the board is assembled. I suppose we may have began by becoming the parts, and sandwiching the boards final, however that seems like a recipe for catastrophe.

The drill diameter for the vias is 0.25mm, which places us simply into the second tier of board pricing (virtually the entire most cost-effective PCB gives have minimal 0.3mm). It might have been potential to do a format of 0201 LEDs inside the most cost-effective tolerance, however I did not wish to threat it. Keep in mind the gap from one LED to the subsequent is 1mm. At this kind of scale, the copper thickness round a plated gap is noticeably uneven.

Solder sandwich

As standard, I mixed postage with a number of different orders, which results in a mini-christmas once they all arrive.

The primary show is an 8×8 matrix at 1mm pitch. With the corners lower off to suit into the spherical profile, that provides as much as 52 LEDs inside a 9mm diameter circle. The panel high and backside is 5mm huge. The entire panel is 23mm by 28.5mm.

I stencilled paste onto one of many boards, and sat an unpasted board on high of it. The symmetrical panel helps guarantee good alignment.

The entire board thickness is 0.6mm, so our sandwich finally ends up a bit of over 1.2mm. This was reflowed in a reasonably uneventful approach.

I most likely ought to have used increased temperature solder for this step, as it could cut back the chance of those joints separating in a while. However, I did not wish to threat messing this up, these pads are nonetheless fairly small at 0.5mm diameter and it is not like I maintain an entire vary of solder pastes in inventory. (They’ve a shelf life, and go off after a number of months anyway.)

Paste paste paste

I ordered a metal stencil together with the boards. I match about six different designs into it, however even ordering a stencil for one board is often viable, they’re unbelievably low cost for what they’re.

My first mistake was not placing the fiducials on the stencil. Aligning the primary board was simple sufficient, we may use the QFN pads to verify it, however after reducing one board out of the panel, aligning the second board was very tough.

My second mistake is probably making the holes for the 0201 pads too small. I most likely may have gotten away with a smidgen bigger, which might have made the stencilling course of much less irritating.

The primary try wasn’t too shabby, most of these pads are good with only a few under-pasted. I wiped this off and tried once more a number of instances, I really feel like with precisely the correct quantity of stress and pace with the squeegee it ought to be potential to get it good.

I did not fairly handle perfection, however bought shut sufficient to really feel like transferring onwards. I did clear the stencil at this level, however not sufficiently. The remaining residue would dry up and trigger me to have a a lot much less enjoyable time when it got here to the second earring.

Decide and place

Presuming the reader has already watched the video, or not less than perused the earlier tasks of the badge and the volumetric display, it goes with out saying that I deliberate to place the components with the decide and place machine.

0201 is nicely past the required tolerance of it, so this was one thing of a raffle. It is not not possible to position 52 0201 LEDs by hand if it got here to it, however I used to be actually curious to see if I may do that, and if that’s the case, what additional tasks that opens up in future.

The machine got here with a collection of vacuum nozzles, most of that are cylindrical, however the very smallest is that this form.

That rectangular tip is a comparable dimension to the components we’re making an attempt to select up, so it wasn’t clear if this might work, however in the long run it did not appear to have any issues on this side.

The development of the machine seems to be little greater than a glorified 3D printer, however evidently it is constructed to a a lot sturdier tolerance. As soon as I might calibrated the place of the parts, it positioned the primary one completely spot-on.

The issues I initially encountered have been much less about element placement and extra in regards to the tape misbehaving. I’ve the machine on a really sturdy desk, but it surely nonetheless shakes about because it operates. This implies components as small as an 0201 LED are prone to go flying if the protecting movie on the tape is pulled again. The holes within the tape are at a 4mm pitch, similar to all the opposite tapes, and most components, even fairly small ones, are positioned at a 4mm spacing. It is solely while you get to 0402 and 0201 that components are positioned at a more in-depth spacing than the holes within the tape. This poses one thing of an issue for the mechanism used to advance the tape: the pinnacle has a solenoid pin which it inserts right into a gap and pulls it forwards. For tapes with a 2mm spacing, it must advance by half a step as an alternative of a full one.

The machine is ready to do that, however the important thing consider getting it to select components reliably was to offset the place of the place it picks up the half out of the tape. The zero place is nearly 4mm away from the world the place the movie is peeled again, which supplied far an excessive amount of leeway for components to bounce away.

I am going to quick ahead to the tip of the primary try.

All in all I used to be fairly impressed with that. There’s an apparent systematic error, the entire components are a bit of too low, however that is simply my inaccurate calibration, the location may be very in step with itself. Just a few of the components are skewwhiff, it is not clear in the event that they jumped as they have been put down, or if there was an error within the imaginative and prescient system. Even a small rounding error within the OpenCV define logic may result in it inserting the components at a bizarre angle. Fortunately it is trivial to push the odd half again into place.

After reflow, nearly all of them snapped into an ideal grid alignment.

The result’s fairly a bit extra constant than my second try on video, simply because I did a a lot worse job of stencilling the paste that point.

Populating the again of the board was considerably uneventful.

Uneventful, however not with out suspense! It wasn’t till this level we get to test if any of it really works after all.

Candy.

After chopping this out of the encircling body, we took a second to do some self-importance pictures with a coin for scale.

The 50p coin is after all a bit of massive, so here is one other shot on a 5p coin, far more applicable.

Stud preparation

Underneath the plastic gemstone, the stud earring has a tiny circuit board with two parts on it.

The case is the optimistic terminal of the battery. The unfavorable terminal is a superb wire via the center of the put up. We simply want to attach our circuit to those two factors.

Fairly short-sightedly, I soldered the connections in place and set the circuit with out absolutely testing it. I used to be exceptionally cautious with setting the prongs, which was foolish as I quickly needed to undo this and modify issues.

The facility draw of my unique firmware was far too excessive, it is dumb I did not see it coming. The teeny battery cannot address the present draw, the voltage drops and the CH32V003’s brownout detector resets the chip. With some additional digging into the datasheet it is likely to be potential to disable the brownout detector. I am extra used to the ATtiny chips, lots of that are blissful to run right down to 1.8V.

It’s nearly potential to reprogram the circuit with it set in place, I exploit a crocodile clip to attach the optimistic terminal, contact one wire to the tip to make the bottom connection, after which contact yet one more wire inside to make contact with the debug pin. Nevertheless, doing this greater than as soon as is a proper ache, so I opened up the earring once more to do issues correctly.

Whereas we’re at it, including some capacitors is sure to assist.

That is a 22uF and a 0.1uF in parallel. Generally large-value, bodily small ceramic capacitors have a excessive inner resistance so it may be useful to mix a number of values in parallel like this.

I dropped the clock pace of the chip from 48MHz to 1.5MHz, and one of many issues I discovered is that this impacts the debugger connection. Ordinarily that is superb, there is a utility that allows you to “unbrick” the chip by energy biking it and instantly connecting. This sadly necessitates debug management of the ability provide, which is why it turns into very fiddly in our scenario, and is what led to me making an attempt to connect with the earring put up with crocodile clips.

Ultimately I bought the show right into a state I used to be pleased with, an obligation cycle of about 0.25% and the decreased clock pace means the general energy draw is one thing like 8mA.

With that, we have been in a position to name it achieved, and start work on the second, which had the added enjoyable of a video digicam in the way in which of the whole lot.

Self-importance pictures

You’ll have clocked a certain quantity of self-doubt I expressed as I got here to set the circuit. It is a formidable electronics undertaking, however is it an earring anybody would wish to put on? To be honest, it is not like that is stopped me previously from constructing utterly tasteless earrings that nobody can be seen lifeless with.

However my good friend appeared fairly eager to strive on extra glowy glowy equipment. I believe she secretly loved being an ear mannequin.

One thought I might meant to strive with the economic piercing is combining a protracted publicity with flash, to attempt to get a nonetheless picture with LED trails.