Boron GPIO provides less current than Electron's GPIO?

boron
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#1

I used in an Electron project its D0 (set to OUTPUT, HIGH) in order to power a load cell amplifier (HX711). Also, this allowed to switch off the load cell amplifier while the Electron is in deep sleep mode.

The load cell amplifier works also with the Boron (here D2), but the load cell amplifier is underpowered when adding the second load cell (in parallel) to the load cell amplifier, the D2 voltage drops from 3.3 to about 2 VDC.

Do the Boron GPIOs provide less current than the Electron GPIOs?
As an alternative power supply for the load cell amplifier, will the 3.3VDC be disabled during deep sleep?


#2

The datasheet for the HX711 says normal current use is 1.4mA. A GPIO should be able to handle that or even double. What else do you have hooked up to the GPIO? A schematic would be helpful. Any code you can share as well?

Boron docs say GPIOs can put out 14mA max. That is a reduction when compared to the Electron which IIRC was 20mA max.

https://docs.particle.io/datasheets/cellular/boron-datasheet/


#3

I noticed this on the Sparkfun page:

How did you wire VCC and VDD when using the Electron (when it worked for you) ?
Did the HX711 operate with more than 1 load cell attached (when using Electron) ?


#4

I measure 2.7 mA (@3.3V pin) just for the HX711, without any load cell attached. Attaching both load cells, the current increases to 18.2 mA, which would be above the comfort zone of 14 mA (GPIO pin).

Putting several GPIO on HIGH and wire them in parallel improves the situation, but the voltage will get not higher than 2.7 VDC which is just the lowest level for the HX711.


#5

For the Electron (when it worked for me): I wired the VCC and VDD to one GPIO, and this worked with two load cells attached to the HX711.


#6

@blub, you will most likely need to add a transistor to drive enough current to power your devices.


#7

That mostly explains why the HX711 + (2) load cells worked with the Election, and not a Boron (spec’d @ 20 vs 14 ma) .


#8

Yes, unfortunately, the lower current spec of the Boron seems to be the problem, i.e. the Boron is not just an improvement of the Electron, it is a different microcontroller.

I would be also happy to use the Boron’s 3v3 supply pin (which works for me), if one could switch off the 3v3 when putting the Boron in sleep mode (deep).

I hope one of the new sleep modes will allow to switch of the 3v3?


#9

You can use a FET to power down the sensor when going to sleep.
You can also power down the 3v3 pin by pulling down the EN pin, but then your device is not sleeping, it’s deactivated till you let go of the EN pin again.

But if you want to know more about that you can look at the Boron schematics
https://github.com/particle-iot/boron/blob/master/pdfs/boron-v1.00-schematic.pdf


#10

@ScruffR Thanks for the hints!

Still, can you tell if it would be technical possible to switch off the 3v3? Or is this “hard-wired” and a potential future system.sleep() can’t switch it off?


#11

@blub, it is not possible to turn off the 3V3 supply and still have the Boron operating since it uses 3V3. The EN pin on the 3V3 regulator is “hard wired” to be externally controlled. As @ScruffR and I said earlier, the ONLY way to control 3V3 to your peripherals is via an external transistor/FET.