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I am working on an IP67 device that contains 3 AAA lithium batteries. The device casework is a 2-piece, hard plastic clamshell with a rubber gasket (think 1/32" O-ring type material) between the halves.The halves are secured with 1/4" long self tapping screws directly into the upper plastic housing.

I need to disable the batteries during shipment and have a mechanism for the end user to enable the batteries once received. The challenge is that the device is IP67 rated and I'd like to maintain that rating. I also would rather not retool to change the current casework.

Does anybody know of a completely internal method to disable the batteries for shipment, then, by the end user performing some action, the batteries are enabled? I say completely internal because I do not want to jeopardize the IP67 rating by passing a plastic strip through the O-ring gasket. Conversely, does anybody have experience with passing such strip through a waterproof enclosure successfully?

Thoughts?

Zhemagen
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  • I can think of a lot of fun and convoluted ways, is _be practical_ a requirement? :) – pipe May 05 '23 at 15:24
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    Internal reed switch, and a tiny magnet stuck to the outside of the case - to be removed by the user to activate the device. – brhans May 05 '23 at 15:29
  • Ship it disassembled, to be assembled by customer. Less work on your part also. – rdtsc May 05 '23 at 16:39
  • @pipe ... yes, unfortunately, it needs to be practical... and obey the laws of physics :) – Zhemagen May 08 '23 at 12:01
  • @rdtsc security is one of the main drivers of this project. We don't want the end user to have (easy) internal access to the device. We don't want it to be easily disabled after activation (batteries removed). This is why we want to send it sealed and active – Zhemagen May 08 '23 at 12:04

2 Answers2

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My first choice would probably be a IP67 rated switch on the case. If that's too expensive then I might try a gasket with a tab, that would also have its own expenses. If the gasket was designed to go immediately around the tab and then self seal after the tab is pulled out, it could be made to be IP67 compliant. In my mind it should be possible to make a pull-out tab that is IP67 rated but that's more of a mechanical engineering problem than a electrical one.

Voltage Spike
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Since security is paramount and the device is to be sealed and not opened once activated, consider a magnetic "one time actuator." A reed switch is a very practical idea, however what prevents an attacker from applying another magnet to turn the device off?

So either electrically latch the first turn-on, or mechanically latch it.

  • Electrically could be with a logic-level N-channel Enhancement-Mode MOSFET across a reed relay at the negative battery terminal - once the relay activates, the MOSFET gate is charged (shorting the relay) and continually powers the device. The device keeps the gate charged, so the relay is effectively bypassed. There is a tiny gate current requirement (nano-amperes.)
  • Mechanically by a latching relay. This type of relay "sticks" intentionally and only needs pulses to latch in either direction. So activating the reed relay pulses the latching relay, and now the device is on for good. No current draw once latched. If a microcontroller is used, could add additional logic such as "when ten reed relay detections occur at 0.234s intervals and within 50ms of each other, turn latching relay off." That way, final testing can be done before shipping, with little chance of anyone ever accidentally discovering it has an "off" feature.
rdtsc
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