# Question regarding hardware design for a datalogger watch

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#### Sink0

##### Full Member level 6
I am designing a project that is very similar to TI MSP-WDS430BT2000D kit (https://www.ti.com/tool/msp-wds430bt2000d). My design would need rechargeable battery, be Water-resistant and to have some way to talk to external world without opening it, and be rugged to external environment (shower, swimming poll and so on). The current version is using a push-pull transformer in order to create a isolated interface to recharge the battery and iRDA interface to communicate with the external world. That is working and got a good level of isolation and protection. However looking at MSP-WDS430BT2000D specifications, it seems to have a spy-by-wire interface exposed to connect to the clip and exposed pins to recharge the battery.

I was looking at some photos at this website, and it seems to have no real isolation from the external world. Just clamping diodes as i a can see in the picture. Is that a proper protection for the internal circuit considering that the watch will be used in all environments a person can go?

Am i over protecting my circuit?

Regards,

LR

##### Super Moderator
Staff member
I have wondered what protection is adequate against static charge. Seems to me manufacturers would put zeners (clamping diodes, etc.) in strategic places.

Some protection is provided by the fact that the device is in its housing. Then it can be at 10 kV overall, safely, because the charge exists on all circuitry. But if the device were out in the open then a single spark at some odd location might ruin the entire device.

#### Sink0

##### Full Member level 6
I have wondered what protection is adequate against static charge. Seems to me manufacturers would put zeners (clamping diodes, etc.) in strategic places.

Some protection is provided by the fact that the device is in its housing. Then it can be at 10 kV overall, safely, because the charge exists on all circuitry. But if the device were out in the open then a single spark at some odd location might ruin the entire device.

I am sorry but i could not get your point about my question....

##### Super Moderator
Staff member
I suppose I was speculating on the possibility that a couple of clamping diodes might be enough, as long as those few connecting pins are the only path for any static charge to be able to contact your device.

Consider that manufacturers must protect a watch from exposure to everyday static charge. You walk across a rug in dry cold weather, wearing an electronic watch. You charge your body to 10 kV. What about the watch?

It is also at 10 kV.

But it continues to work. It's okay as long as long as the static charge is equal in every component inside the watch. Apparently that is adequate protection.

#### Sink0

##### Full Member level 6

One question. I am considering use USB as the communication and communication port and use a TPD45014 to protect my device. Thinking about the exposed ground pin. Would i have any benefit of adding a Ferrite Bead between the pad and system ground? Any downside when i connect the USB port to start charging the device?

Luis

##### Super Moderator
Staff member
I am considering use USB as the communication and communication port and use a TPD45014 to protect my device.

I have no experience with the TPD45014. It doesn't show up in an internet search.

Thinking about the exposed ground pin. Would i have any benefit of adding a Ferrite Bead between the pad and system ground? Any downside when i connect the USB port to start charging the device?

Sorry, I can't know what will or won't work. All you can do is try to solve problems that come up. You can expect to have to put your device through a series of trials under various conditions.

You may or many not be able to find out what safeguards are installed in cell phones, cameras, etc.

As long as you're concerned, you might consider cordless charging, since your device is small and portable. It's being done with hearing aids, etc. (I don't think it can work through a metal housing.)

It's done by sending AC through a coil in the charging base. Your device needs to be close by. It contains a coil made to resonate with the magnetic field from the base. Send the AC through a diode bridge to charge the battery.

#### bigdogguru

I am designing a project that is very similar to TI MSP-WDS430BT2000D kit (https://www.ti.com/tool/msp-wds430bt2000d). My design would need rechargeable battery, be Water-resistant and to have some way to talk to external world without opening it, and be rugged to external environment (shower, swimming poll and so on).

Out of curiosity, have you taken a look at TI's other watch development tool:

The design utilizes a CC430F6137, subGHz RF SoC, comes with a wireless bootloader for firmware updates and while it doesn't offer a rechargeable battery, I've been using the device to development an application for over a year using the original watch battery.

The watch also provides an internal JTAG interface for debugging and programming if need and is water resistant.

TI seems to sell the eZ430-Chronos Development Tool for half price, $25 at least once a year. I now have six units with various RF frequencies. BigDog #### Sink0 ##### Full Member level 6 I have no experience with the TPD45014. It doesn't show up in an internet search. Sorry, it was suposed to TPD4S014. About wireless charging. We considered the option and still, but as is a low volume product i would need a COTs antenna, and could not find any that could fit inside ou housing. Do you know any wireless charging receiver antenna vendor? Regards, LR - - - Updated - - - Out of curiosity, have you taken a look at TI's other watch development tool: **broken link removed** **broken link removed** The design utilizes a CC430F6137, subGHz RF SoC, comes with a wireless bootloader for firmware updates and while it doesn't offer a rechargeable battery, I've been using the device to development an application for over a year using the original watch battery. The watch also provides an internal JTAG interface for debugging and programming if need and is water resistant. TI seems to sell the eZ430-Chronos Development Tool for half price,$25 at least once a year. I now have six units with various RF frequencies.

BigDog

Sure, i have one and have studied it a lot. One interesting fact is that the back stainless steel part seems to be short circuited to system VCC. Also, when buttons are pressed the VCC is short circuited to MCU pins, with not even a series resistor. I might have understood wrong but cant see other way to power the back piezo buzzer.

Regards,

LR

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