Design of Secure Tab E 9.6 Enclosure for Smart Cabinets Inc (SCI)

The original reason this project came through our doors was that SCI wanted to extend the life of the batteries in the tablets that are at the heart of their AED training kiosks. They asked Samsung for a solution and were referred to Lava and our battery modulation technology. It was then found that their product itself was quite flawed and I was tasked with redesigning it.

The original product involved building a custom AED door, and mounting to it a tablet along with a speaker. The problem with this is that they would then be required to ship big doors all over the place after assembling their electronics into it, which would quickly get expensive. It was proposed that the electronics be assembled into their enclosure, so that all electronics assembly and testing could be done in one place, and then the electronics could be shipped without disassembly to the end customer, whether that be an AED manufacturer like J&L, or an individual owner of and AED cabinet that could install it as an upgrade. It was also proposed that the electronics package mount externally, such that all it would take to install the kiosk package would be the drilling of a few holes, with no large shaped cuts being necessary. This new design also holds the large advantage of being much easier and cheaper to ship, as SCI will now never be responsible for shipping of the door itself, only having to ship the significantly smaller electronics package. It also allows them to centralize their assembly and QA wherever they want, as they are no longer tied down to the source of the difficult to ship doors. It should note that this is very important when dealing with tablets, as they typically need to be tested “burn in” style for a few days, which a metal manufacturer like J&L would not want to/be capable of doing.

The next major change introduced by lava was the replacement of the speaker in the original design with a mechanical parabolic amplifier. The previously perceived need for a speaker was largely a bi-product of the cheap Chinese tablet that was originally planned for use in this design. It was realized that a small (~15db) amplification of SCI’s original audio track and the addition of a few pieces of parabolic shaped acrylic would result in a sound more than loud enough for SCI’s application. This simplified the design and supply chain, as adding a speaker would have necessitated a much larger enclosure and would have added about 5$ of additional cost per unit.

The requirements of the design were than considered. As almost always, the design should be as cheap as possible to produce, so more complicated metal processing methods (sand casting, CNC machining) were out of the question, which left sheet metal as the only viable option. The usability of the device was considered, such as the need for the device to be powered on and off without being removed from the enclosure, but not in a way that is so obvious that teenagers will be able to figure out how to mess with it. The security of the device was also considered, such as being able to survive an attack from a flathead screwdriver, which was stated mathematically as 5KN applied anywhere on the enclosure. From this, calculations were performed, which suggested that the public facing front panel should be at least 1/8” thick, with the internal components being as thin as 1/20”.
At this point, the effect on a semi-full steel enclosure on the strength of RF signals being sent and received by the tablet was evaluated. It was found that a steel coverage similar to what the tablet would be experiencing in our enclosure would result in a weakening of 2.4 GHz wifi signals of about 30%, which did not have a measurable effect on Up/Down speeds or latency. It was decided that this level of attenuation was, therefore, acceptable.

The real challenge to do with the design of this enclosure is that it will at some point have to be produced in the thousands, and as such must be easy to manufacture. Sheet metal design guidelines were studied and had to be followed to the T. This was done largely successfully, with the only exception being one small hole that would not be a producible using tool and die, as its diameter is about half of the material thickness. If this largely impacts the cost of manufacturing (yet to be determined), a different design will have to be employed, which will likely involve replacing the steel in that section with a small acrylic cutout.

At this point, multiple designs were sketched up, and a simple rectangular shape made of 4 distinct sheet metal parts was settled on. It connects to the AED enclosure door with four 10-24 studs, which can only be accessed by opening the door of the enclosure which will set of a 130dB alarm, quite a strong deterrent for tamperers. It completely encloses the tablet and has a ½” access hole for a USB cable which will lead to a plastic enclosure to be stored in the cabinet which will contain Lava Tech along with a switching power supply.

This product has been sent out for prototyping. A future post will detail the changes made as a result of such.

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