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RingGesture: ToF VL53L5CX for finger and hand gestures


My project makes progress, see here: 

My question:

When I set LPn low - is just the I2C disabled? Or would also an initiated ranging stop?
In order to save power: is there a need to set via I2C the mode, or would LPn low already bring the sensor into low power mode? (I am not convinced based on what I have studied in the datasheet).

Another question:

The RES signal on ToF sensor: does it reset the entire chip? As I understand, just the I2C is reset. In order to reset the entire chip, I had to toggle also both VDDs.

I have realized: when the chip is messed up (e.g. still running a range scan configured), just toggling RES is not enough. I need a power cycle of entire setup. Is this expected as "reset behavior"?

ST Employee

LPn is the worst named pin ever. I suspect early in the design it was supposed to be LPn, but it evolved into simply an i2C off pin. I think the call it 'comms enable'.

To save power, you can issue the 'Stop' command. That should do it. 

But if the sensor is 'messed up' for some reason, and toggling the LPn (to clear i2c errors) your best next step is to indeed drop the VDDs.

- john

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I agree:
LPn can mean LPx (and x for a number). Often we see nLP, telling me it is low active signal.
Instead of toggling VDDs (which I do not have as an option, just entire setup unpowered vs. powered), there is also nRST (which should reset the I2C on ToF sensors - wired, but not used yet).

So far, it works OK. Sometime, the ToF sensor config is messed up, I do a full system power cycle right now.

The 'Stop' command?
Yes, I enable ranging or disable it again (it should be the 'Stop'). Afterwards, I set LPn low for the current sensor. I "hope" it goes into lowest power mode, before I select and do the same with the next sensor.

My understanding:

  • just to stop the active ranging mode (via "Stop") is not yet the lowest power mode
    (just enters HP IDLE)
  • it needs also LPn low for the inactive sensor (what I do before changing to a different sensor)


LPn low for "LP IDLE" should do the trick.
But I think: you cannot go from "RANGING" just via LPn low directly to "LP IDLE" (what I have realized). It will not stop the active ranging (I did by mistake and saw still a huge heat generated, on all sensors, because all remain "active ranging", even LPn goes low!

Thank you.