I2C issue

All ESP8266 boards running MicroPython.
Official boards are the Adafruit Huzzah and Feather boards.
Target audience: MicroPython users with an ESP8266 board.
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isaburi
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Joined: Fri Nov 18, 2016 9:01 pm

I2C issue

Post by isaburi » Fri Nov 18, 2016 9:13 pm

Hi all,

I have a pyboard and a esp8266 module with firmware mycropython. I want to connect the esp8266 module with 3 devices through I2C but my esp8266 only scan 2 devices. The device work well because when I scan with the pyboar, it detect the 3 devices.

The esp8266 and the 3 devices are in a small pcb so there should be no problems with the I2C connection.

I do not understand what is happening.

I hope you can help me. Thanks

Regards
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kfricke
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Location: Germany

Re: I2C issue

Post by kfricke » Fri Nov 18, 2016 11:18 pm

How many pull-up resistors are on your bus? Maybe the pyboard is more tolerant in this regard?
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deshipu
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Re: I2C issue

Post by deshipu » Sat Nov 19, 2016 1:00 pm

I would also help if you told us what the devices are.
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isaburi
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Re: I2C issue

Post by isaburi » Sat Nov 19, 2016 2:13 pm

I have a 2k2 pull-up resistor in scl y sda as said the datasheet of my esp8266.

The devices are 3 sc16is752, you can see the devices in the following link
http://www.nxp.com/products/interface-a ... _SC16IS762

Thanks for the help. And sorry for my bad English.
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deshipu
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Re: I2C issue

Post by deshipu » Sat Nov 19, 2016 8:16 pm

Can you link to that datasheet that claims you have 2k2 pullups?
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isaburi
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Re: I2C issue

Post by isaburi » Sun Nov 20, 2016 3:40 pm

Sorry, I can not find the data sheet now. Do you think the problem is the pull-up?
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deshipu
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Re: I2C issue

Post by deshipu » Sun Nov 20, 2016 7:54 pm

It is a common cause, and I've never heard about a board that has 2k2 pullups built-in. But of course it's hard to say for sure. I would recommend testing with additional external pull-ups.
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Roberthh
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Re: I2C issue

Post by Roberthh » Mon Nov 21, 2016 6:38 am

If that matters, you can measure the value of the pull-up, either directly as the value of the resistor, or better determine the current to GND., by setting the respective port to input, high impedance and then take the current when that port is connected to GND via the Ampere-meter. With 2k2 as a pull-up, the current reading should be about 1.1 mA. The pull-up value is about 3.3/I, where I is the current seen (R = U/I), ignoring the voltage drop at the instrument here (note to nitpickers).
I would recommend testing with additional external pull-ups.
Wouldn't these be parallel to the internal pull-up and even lower the pull-up impedance?
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deshipu
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Re: I2C issue

Post by deshipu » Mon Nov 21, 2016 10:24 am

Roberthh wrote:
I would recommend testing with additional external pull-ups.
Wouldn't these be parallel to the internal pull-up and even lower the pull-up impedance?
Yes, if they are there. I'm betting on a case where they are missing. Worth a try, in my opinion.
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