GY type breakout parasitic current draw.

  • Right now I'm really banging my head on the wall because I'm lost. I have been using an outdoor sensor unit for the last two years now. The heart is a Moteino on a perfboard carrier. Connected to the Mote are 2 GY boards; a GYBMEP with a Bosch BMP-280 and a GY-49 with a MAX44009 light sensor. The whole device is powered by a 1000mAh LiPo topped up by a small solar panel through a ADA390 solar charger (MCP73871).
    See the picture for a little overview. 0_1545340876187_domotica-011.jpg

    My problem is this: when de Mote sleeps, I can't get the current consumption of the sensor boards anywhere NEAR the specced values (0,65uA for the MA44009 and 0,1uA for the BME280). I end up at about 800uA for the sensor boards alone. So first I used software to switch off the power and I2C bus to the sensors, but that does not work because the MAX44009 needs 800ms to take a measurement, and to wait almost a second every time for the sensor to finish feels kind of stupid. So powered continuously it is. Should not be a problem with the specified power consumption. I already had removed the linear regulators for both boards to be able to use lower voltages.
    So next step; remove the resistors and MOSFets that protect the sensor from overvoltage from the GY boards. A bit of a fiddle because teeny tiny, but I think I succeeded. I dit get a lower current draw, about 300uA. But that's still nowhere near the 1,5uA it should be.

    Does anybody around here have had the same sort of phantom draw? And has that person found a way around it outside of using the bare sensor chip? I simply can't solder that stuff.

    I know there are some other kinks with this board, the regulator on the Mote goes into some sort of avalanche mode when the battery voltage goes down to Vout + Vdropout. It then passes around 90mA all the time. I've had that happening twice now: a year apart to the day. And the charger board also uses 35uA whatever the state. But that should not be a problem during the day.

    I really want to solve this now so that I never have to take a second look to that sensor. Hints are appreciated.

  • Mod

    Personally I like the SHt31 sensors better for outdoor use. With my node I am in 5uA sleep current

  • Thanks Gohan,

    there are a few reasons for me to use the BME outside. The most important: power management (and that explains my conundrum now...).
    The unit contains a light sensor. That basically controls my lighting in the living room. So that needs to measure quite often to be able to control it with any accuracy. I've chosen every minute as a basis. That was also given when I found a sketch with a weather prediction function based on barometric pressure. That sketch needs to read the pressure every minute. That means that the sensor wakes up every minute. Also the radio. That's a huge load. Not really ideal for battery power. But that meant I was able to add the light sensor very easily.
    So now I put them in an outdoor sensor with a solar panel to keep the battery topped up. That still means I have to watch the consumption in sleep. Here in NL we have quit a few overcast days, so the panel will not be able to keep up with the demand on those days.

    The solution in place now is to wake up the sensor 1 second before measurement. Power up the sensors, put the controller and radio back to sleep for one second. Then do the measurement stuff, power down the sensor and I2C bus and go into deep sleep. Average current consumption measured over 4 hrs is now 140uA. Sleep current for the whole system is 36uA. That is including the charger board and Moteino voltage regulator.
    The unit is now up for 3 weeks and the panel keeps up very good. Most of those days were overcast. So when the cold hits next week with clear skies it should be full all the time.

    Battery level is sent every 6 hours. And next to that I have implemented a voltage measurement that signals when the battery is being charged. Energy is coming in, so I am allowed an extra data transfer... 😝

    Now see if it dies on me again end of november 2019...