ESP8266 Community Forum

- Thu Jul 06, 2017 8:04 am #67973 I'm starting a new project that uses the ESP-12E, 3.3v switching power supply and I2C temperature/humidity sensor.

I've done a bit of reading up and have noted:
-the FTDI USB chip will not be on the board drawing power. I can program the ESP through a connector when needed.
-GPIO16 has to be connected to Reset

My question has to do with pullup resistors on the i2c lines needed for the temp/humid sensor. Wouldn't two 10K resistors on SDA and SCL to +3.3V constantly draw power?

- Thu Jul 06, 2017 8:19 am #67974 I have a BMP18 I2C module and it already has pullup resistors on board. Check it on your module. These resistors should generally not increase the power consumption because the I2C bus is designed as an open collector. Therefore, the pullup resistors must be connected to the bus.

Last edited by jankop on Thu Jul 06, 2017 8:23 am, edited 1 time in total.

- Thu Jul 06, 2017 8:20 am #67975 The pullups only draw/pass current when the I2C bus gets pulled low, which is only during communication. During sleep, there is no communication. Hence, the I2C bus is connected to high impedance inputs and floating at 3,3V.

- Thu Jul 06, 2017 9:42 am #67978 most of modern sensors are 3.3V but boards are designed for standard arduino with 5V, so they not only have pullups on board but also voltage regulator and i2c level shifters.
Just as info if you observe unexplainable power drain.