INVERT the sense of the I2C_POWER pin (active low)

[anecdata]

I don't have the board to test, but this was reported and discussed on Discord. Probably only relevant for the BME280 version of the board.

[jerryneedell]

From the schematic, VSENSOR also goes out to the STEMMA connector - so this may also impact the non BME280 version

[jerryneedell]

Unfortunately, today, I have been unable to get it to fail regardless of whether the I2C_POWER pin is set to True or False...

[jerryneedell]

this is the code I am using to test -- I just change the ip.value from False to True but today , it does not seem to care.

# SPDX-FileCopyrightText: 2021 ladyada for Adafruit Industries
# SPDX-License-Identifier: MIT

import time
import board
from adafruit_bme280 import basic as adafruit_bme280
import digitalio

ip = digitalio.DigitalInOut(board.I2C_POWER)
ip.switch_to_output()
ip.value = False
# Create sensor object, using the board's default I2C bus.
i2c = board.I2C()  # uses board.SCL and board.SDA
bme280 = adafruit_bme280.Adafruit_BME280_I2C(i2c)

# OR create sensor object, using the board's default SPI bus.
# spi = board.SPI()
# bme_cs = digitalio.DigitalInOut(board.D10)
# bme280 = adafruit_bme280.Adafruit_BME280_SPI(spi, bme_cs)

# change this to match the location's pressure (hPa) at sea level
bme280.sea_level_pressure = 1013.25

while True:
    print("\nTemperature: %0.1f C" % bme280.temperature)
    print("Humidity: %0.1f %%" % bme280.relative_humidity)
    print("Pressure: %0.1f hPa" % bme280.pressure)
    print("Altitude = %0.2f meters" % bme280.altitude)
    time.sleep(2)

[anecdata]

@jerryneedell Do you have a Rev.A board?

[jerryneedell]

How can I tel if it is Rev A?

[anecdata]

On the silk, in theory

[jerryneedell]

I don't see any indication.

[anecdata]

huh, maybe only gets the silk treatment when it changes to Rev.B

[jerryneedell]

The schematic I saw is Rev B -- what changed from Rev A?

[ladyada]

rev A did not have power control

[jerryneedell]

How can I tell Rev A from Rev B board?

[jerryneedell]

I am looking at the V+ pin on the STEMMA connector with a scope. If I set I2C_POWER to False, it stays steady at 3.3V.
If I set it to True, then the voltage drops just below 3V and when the BME280 sensor is accessed, it drops briefly (10ms) to <1.5 V. Does this sound like Rev A or Rev B?

Note: the BME280 sensor is working with both settings of I2C_POWER -- I saw one failure when it was True, but cannot reproduce that.

[jerryneedell]

sorry -- the votls/div was set to 1.04 for these shots... but you get the point...

I2C_POWER = True

I2C_POWER=False

[ladyada]

you're probably seeing parasitic power thru the I2C pins. you definteitely need to pull the power pin low to access i2c

[jerryneedell]

@ladyada should I assume I have a rev b board.? Is there a way to tell?

[ladyada]

if you're not me or i think scott, you have only a rev B board. we never shipped rev A thru the shop :)

[dhalbert]

Thanks, this is good!