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pasko-zh / brzo_i2c

Brzo I2C is a fast I2C Implementation written in Assembly for the esp8266
GNU General Public License v3.0
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Question: Logic Levels and ... #26

Closed Eddiiie closed 6 years ago

Eddiiie commented 6 years ago

Hello,

I have a question. ESP8266 is using 3.3v on the GPIO pins, right? I am assuming most I2C devices are 5v.
Are you assuming a logic level converter is in use or is there no issue between the 3.3 and 5v. OR am I just wrong and all I2C is 3.3v?

Unfortunately, I forgot the second question. grrr

pasko-zh commented 6 years ago

Hi Eddiie,

  1. Yes, the esp8266 has 3.3V on the pins
  2. Well this depends, up to now I have found all i2c devices that I need with 3.3V :smile:
  3. Most breakout boards with i2c devices include already a logic level shifter, e.g., Adafruit's HTU21 Breakout Board. However, be aware that those boards may have a built-in pull-up resistor with a very high resistance (in i2c jargon this is referred to as "weak pull-up", because the current flowing through is very weak). Such a high resistor will leave you with terrible raise times, so a smaller value ("stronger" pull-up) is needed. See my comments for HTU21D with brzo_i2c.
Eddiiie commented 6 years ago

Thank you for all of that information. I am working with a device that is most likely expecting 5v levels. It is not working currently with the ESP8266, will try adding level shifter and see, maybe do a capture to see what the bus looks like.