Embedding Electronics in Transparent Resin

I’ve been wanting to play with embedding electronics in clear resins. Someone on twitter suggested that jewelery resins might work well. So I picked some up. Here are my initial results. This is the kit I purchased on eBay.h Here’s the complete contents:

All the junk you get in the kit.

I really only needed the resin, but I couldn’t find it separately (I’m sure it exists) and figured some of the other parts might be of use. There’s no documentation whatsoever however it’s reasonably clear that this is the 2 part resin.

I mixed it up in the supplied beaker using the ratio shown on the bottles (2.5:1). I mixed everything together for a couple of minutes. A lot of air gets into the mix, this doesn’t seem to matter as most bubbles disperse during curing. However, I can see that a degassing chamber could possible improve results.

2 Part Resin

I figured my solar lantern kit (plug: available from my shop) would be a good test candidate, as I often leave them outside for prolonged periods of time. So I placed the assembled lantern in a plastic bag, and used a cup to hold the shape of the bag. I figured this would keep its shape and allow me to remove it from the cup later. I was wrong… I guess some resin leaked out and it was firmly wedged in the cup. I ended up having to break the cup to get it out…

Ideally I think you’d want a custom silicon mold. However a multi-part 3D printed mold in which you can pull apart after curing might work perhaps? If I take this forward I may try this out.

Curing took a long time. It’s been 24 hours so far and its still a little tacky. From what I’ve seen on the Internet 6 to 12 hours is typical, however curing time strongly varies with humidity and I do live in quite a humid region.

After curing the results look pretty reasonable (as shown above). The surface is clear, and the LEDs shine brightly through it. Battery contacts also appear to be strong, though I’d ideally want to weld them in place rather than using a redundant battery holder.

Curing in progress…

Overall, I’m pretty pleased with the results. The resin seems solid and should protect the electronics against the environment well. I need to seal up the solar panel then I’m going to dump the whole thing in the garden for a few months and see how well it lasts. Should be an interesting experiment.

If things go well, I’ll likely try and source larger quantities of the resin and design some custom molds.

That’s all for now, check out the video for more rambling and dunk test…

 

 

 

 

 

 

 

HP Interferometer Notes

I’ve been setting up an interferometer. I purchased the system from siliconsam (of Sam’s lasers) on eBay (this is the auction). He occasionally sells old HP systems on eBay, the advantage is that the laser, optics and receiver come tested.

There is however “some assembly required”. In particular, this kit is based around the µMD1. This is essential a Chipkit DP32 (PIC32 dev board), with some firmware Sam and Jan Beck and a Windows application (written in VB).

The instructions for wiring the Chipkit DP32 are pretty straightforward. The only issue I had was that the diagrams only show the resistor color codes, this is a problem for me as I’m colorblind. However there are 6 of one type and two of the other so it was easy enough to figure out from the parts provided. At some point I’d like to design a custom PCB to avoid all the wirewrapping…

You also have to wire up the optical receiver and laser head cables. Notes on these are below.

10780A Optical Receiver Wiring

The optical receive uses a strange connector. I’ve seen this called a “quad BNC” (also seems to be called 4-pin BNC) and it is a bayonet style connector with 4 internal conductors. Sam’s kit provides cables wired with pins which you prod into the connector, it’s not the most robust solution in the world, but it holds together pretty well.

The 10780A documentation provides the following wiring information:

“Fused +15V RET” is essentially ground. The wiring I used is show below. It can also be found on Sam’s FAQ.

5517B Laser head Wiring

The laser head uses an old multiconductor connector. I think this one. You can find details of the wiring of this connector in the 5517 manual (5517 manual local copy). I’ve also highlighted the wiring of this cable on the screenshot below.

 

That’s it for now. I have a couple of videos on youtube documenting the setup:


At some point in the future I may post more details of the laser alignment process, and the jigs I’ve designed to try and make alignment easier.

Genome Analyzer II Internal Pics

A while back I was lucky enough to encounter a disassembled Genome Analyzer 2. I’ve played with the data from these instruments a lot, having written an image analysis and basecalling platform for this instrument so it was fun to see one on the inside.

The instrument is effectively a TIRF microscope, stage and fluidics system stuffed in a case. As is typical of early versions of scientific lab equipment, it mostly uses off-the-shelf parts stuffed in a case.

For my reference, I took a huge number of pictures. Check them out below:
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Another iPhone MEMS Mic (different configuration+layers)

iphone6smemsToday I pulled apart another MEMS Mic. This was from a replacement flexpcb for an iPhone 6s I bought on eBay. I expected the MEMS sensor to be identical to the one I posted yesterday. But it turns out it was quite different.

Optically it resembled the image shown on the right (from chipworks), with a single diaphragm and 4 bonding pads. Chipworks say this is a Goertek GWM2.

A couple of interesting things happened when I was playing with the 2 MEMS packages on this flex. Firstly, when I removed the package on one device the whole MEMS die came with it.

 

 

This meant I got a view of the underside of the device, this is the side that the sound hits:

 

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What confuses me slightly is that there appear to be release holes on this side of the diaphragm too. I would have expected it to be solid as appeared to be the case in the chipworks images I posted yesterday. The release holes also seem to be a little smaller than the previous sensor. On the order of 7 microns.
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The other interesting thing that happened is that I found I was able to pull the layers away from the mic using a pair to tweezers. I was amazed that the diaphragm remained largely intact. I stuck this down with some polyimide tape and it imaged quite well, this is layer furthest from the sound inlet:

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I even managed to remove the diaphragm “below” this (nearest the sound), but wasn’t so successful at taping it down. Here it is sitting on the back of polyimide tape. I’m surprised how well the sample image without being grounded…

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I’m not sure exactly what is happening in the following image. It looks like this diaphragm maybe more complex. While a hexagonal mesh is present, it seems like there a solid layer behind this (this would somewhat explain the fact that the “sound-side” mesh above looks like it has holes in it). It also seems to have holes of different sizes… I couldn’t acquire very good images here… I suspect the sample wasn’t very stable sitting on the polyimide tape.

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