Adding an I2C sensor - any way to do so in a way that easily turned on / off

sparkfunX / Artemis_Global_Tracker

A global satellite tracker utilising the SparkFun Artemis module, Iridium 9603N satellite transceiver and u-blox ZOE-M8Q GNSS

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Adding an I2C sensor - any way to do so in a way that easily turned on / off #20

Closed jerabaul29 closed 3 years ago

jerabaul29 commented 3 years ago

Hi :)

I want to add the BNO080 to an instrument based on this board. As it looks like we cannot at the moment get really low power with the BNO080, I will have to turn it on / off by enabling / cutting power supply to it.

from the schematics it looks like the Qwiic port is always power on, right (I see no MOSFET controlling power to it)? Or is there a way to turn power on / off on the devices on the Qwiic port?
another possibility would be to put the BNO on the same power ramp as the GPS, and use a GPS low power mode when it is not in use but the BNO is (the GPS has a low power mode if I remember well? :) ). The challenge it seems is to get access to this power rail. I do not see any obvious place where I could easily solder a couple of wires to get power. Or am I missing something?
I guess if both previous options are not possible that I will have to just add a separate small PCB with its own MOSFET or similar, right? Or is there another solution I could consider?

jerabaul29 commented 3 years ago

Ahhh, I see a solution: the BNO080 should be happy with everything above 2.4V according to its datasheet Fig. 6.2, right? :) Then I should be able to tap power from the pins of one of the supercapacitors, right? :) Something like:

putting the iridium modem to sleep
switching on capacitor charging
starting to talk to the BNO

Or am I thinking wrongly?

jerabaul29 commented 3 years ago

(of course that would be a hack, but but, good enough for a prototype / proof of concept to me, and we will design a custom board later on if we are allowed to continue in this direction).

jerabaul29 commented 3 years ago

(I would need just to find which is C5 vs C6 I guess to make sure I have the right ground, but I can check that by hand on one of my boards :) If you can tell which one is the one to use, just for double checking, that would be great though :) ).

jerabaul29 commented 3 years ago

Mmmh, no, checked out in more details, that will not work: the datasheet says the voltage on SDA / SCL should not be over Vin. So not possible to power with 2.7V if the logics are at 3.3V I am afraid.

There is one pad under the ATG that I am curious about: the "VIN/3" mini pad in the rectangle around a supercapacitor. I have a hard time figuring out what it is couple to. Is it on one of the MOSFETs?

PaulZC commented 3 years ago

Hi JR, Ideally, you need the Qwiic Power Switch but it is out of stock at the moment. Correct, the Qwiic power is not switched. My suggestion would be to hook up the BNO080 to the GPS/MS8607 I2C bus using the breakout pins on the left side of the board. You then need to solder a wire to 3V3SW to provide switched power. The easiest places to do that would be at Q2: Or at the GNSS power LED resistor R16: VIN/3 let's the Artemis check the VIN power rail. Actually, that's an alternative for you. You could pick up VIN power from the 'top' of R24 but you must then regulate it to 3.3V before passing it to the BNO080. I hope this gets you going. Paul

jerabaul29 commented 3 years ago

Many thanks for your kind help :) . I will consider either putting it on the GPS LED, or using an additional (I already use 1 to feed power to the board) external pololu regulator, which can be driven on and off through an activate pin.