Dash Power down during Cloud Send safe?


#1

Hi,

I am trying to figure out what the repercussions are if the Dash suddenly loses power after a HologramCloud.sendMessage() is called.

Can the system MCU or ublox radio module get hosed or damaged if a shutdown occurs?

Lets assume that I cannot use a lipo battery for my application and I am strictly running on USB power - so any suggestions to use a lipo battery aren’t helpful at this point.

Thanks in advance!


#2

There should be no permanent damage in that case, however you should not expect the message to get saved anywhere or delivered.


#3

Thanks @Reuben!

For my application I am looking to use super caps to hold up the dash while it completes some housekeeping tasks. One of the hardware modifications I was considering is as follows. Is there an issue with using this method?

I wanted to bypass the charger because its UVLO is so high.

Alternatively I just put the supercaps on SystemVin net.


#4

We had a chat with our hardware engineer about this. Gist is that it should work but to be careful about inrush current.

Here’s his message:

He says that he will put the USB circuitry on a separate board. If that is the case, then, yes use the System Vin pins. But - he must be aware of the inrush current at turn-on that the super caps will present to the USB. It would be best if he were to create a power supply to provide the System Vin which has the super caps on the output of that power supply. This topology would limit the inrush current, and would provide the hold-up during transmission.

Other concern: are you attempting to transmit a message while it’s shutting down? That would spike the power draw and may end up draining the caps before it’s complete.

Also, we were wondering, how will the Dash know that main power has gone away in order to do the housekeeping things?


#5

Thanks for the feedback!

We are using a poor mans inrush limiter to keep the current below the amount that can be supplied by the USB specification.

Other concern: are you attempting to transmit a message while it’s shutting down? That would spike the power draw and may end up draining the caps before it’s complete.

Absolutely - this is just for saving data to internal flash prior to shutdown.

Also, we were wondering, how will the Dash know that main power has gone away in order to do the housekeeping things?

I plan to sample the USB voltage (from before the diode) using the dash. The voltage will be divided down to a safe level for the dash to handle.


#6

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