ESP8266 Community Forum

- Sun Feb 12, 2017 6:07 am #62439 I'm trying to run an HTU21D on a Nodemcu V3 Board (LoLin).
The HTU21D breakout has a solder bridge to enable / disable 4.7k pull-up resistors to SDA and SCL.
Do I have to activate the pull-up resistors on the breakout board or are the resistors already integrated in the Nodemcu, in particular at pin 4 and 5 (D2 and D1)?
Thanks for an explanation!

- Sun Feb 12, 2017 3:56 pm #62469 Hi, GPIOs 4 and 5 do not have pull up resistors, you will need to activate. GPIOs 0 and 2 are comon for I2C and do have 10K pull up resistors so they would not need activating.

- Mon Feb 13, 2017 9:28 am #62494 Thank you for your help!
It now works on pin 0, 2 (D3, D4) with Wire.begin (0.2) and pullup resistors disabled.

If I understand correctly, it should work on all other pins with pull-up resistors enabled.
But I could not manage this. I tried it with pin 5/4, 12/14, 13/15, at 4.7K or 10K, but without any success.
I'm trying only with an i2c scanner, but it does not even recognize the address.
Strange, but it works when I connect two HTU21D over a multiplexer TCA958a (has integrated Pullups) at pin 5 and 4 - therefore I am quite confused ...

I would like operate two HTU21D - for reason of simplicity without multiplexer if possible, similar to here:
http://www.esp8266.com/viewtopic.php?f=29&t=13174&hilit=same+address+i2c#p60404

- Mon Feb 13, 2017 10:51 am #62498 addendum: in the meantime I got a BMP085 and this one works also on the other pins.
It looks so that only the HTU21D has this problem, I can not see why.