Sealed, waterproof BLE device...how to wake up?

[Steve Muebreg]

I'm working on a device which may spend months, or even years as deep as 1000 ft underwater...a harsh environment. Accordingly, the PCB will be completely encased in plastic (potted or overmolded).

We'd like to use the nRF51822 SoC since it would allow data transfer without any penetrating metal pins or connectors that would be avenues for leaks.

The problem? How do we turn on advertising/communication for the very brief episodes when the device is recovered and actually needs to connect to a PC for download.

Normally, one would just add a small button to wake the system up and start advertising. That's not easy in this case.

So what I'm looking for is some other clever and robust way to initiate BLE advertising from outside the sealed unit. A couple of ideas I've had:

• a reed switch or hall effect sensor triggered by a nearby magnet
• an accelerometer to pick up a distinct pattern of "taps" on the casing

Both of these seem kludgy to me, but I'm not sure what else to do.

Clever ideas?

[syntroniks]

I have successfully used a piezo as an io transducer with these devices. A reed switch should work nicely

[Steve Muebreg]

My only reservation about the reed switch is that the end user will have another piece of hardware (the magnet) to keep track of.

Would be interested to hear more about the piezo option, and how you implemented it...

[mtsunstrum]

Consider a photo diode light type detector, connected to nRF51822 GPIO input pin.

Have a translucent window port to the photodiode detector. Have this window port covered normally. Remove, shine light in it, and let it wake up that way ...

[Ken A. Redergård]

Perhaps the internal temperature sensor can be used to trigger BLE advertising ?

If the delta temperature for a time interval is above a threshold it triggers the BLE advertising ? Or perhaps a temperature threshold is enough ?

BR, -Ken.