<![CDATA[WiPy LoPy I2C with ATMEGA]]>I tried to to connect my LoPy with an Arduino Pro Mini @ 8MHz 3.3V via I2C. The results were not the expected.

The reason I want to do this, is that I must count pulses from various devices. ESP8266 and ESP32 are not stable with ISR so I decided to keep the ATMEGA with the bug free hardware interrupts at PINS 2,3. Currently I use Software Serial with UART and it works just fine. But I would like to go further using I2C.

I tested the solution but it didn't work. I was getting wrong bytes from time to time and that's why the setup is considered as not reliable.

Does anybody managed to achieve this?

Thanks
Constantinos

]]>https://forum.pycom.io/topic/1017/wipy-lopy-i2c-with-atmegaRSS for NodeMon, 18 May 2026 06:29:31 GMTTue, 11 Apr 2017 23:03:11 GMT60<![CDATA[Reply to WiPy LoPy I2C with ATMEGA on Tue, 11 Apr 2017 23:03:40 GMT]]>I tried to to connect my LoPy with an Arduino Pro Mini @ 8MHz 3.3V via I2C. The results were not the expected.

The reason I want to do this, is that I must count pulses from various devices. ESP8266 and ESP32 are not stable with ISR so I decided to keep the ATMEGA with the bug free hardware interrupts at PINS 2,3. Currently I use Software Serial with UART and it works just fine. But I would like to go further using I2C.

I tested the solution but it didn't work. I was getting wrong bytes from time to time and that's why the setup is considered as not reliable.

Does anybody managed to achieve this?

Thanks
Constantinos

]]>https://forum.pycom.io/post/6280https://forum.pycom.io/post/6280Tue, 11 Apr 2017 23:03:40 GMT<![CDATA[Reply to WiPy LoPy I2C with ATMEGA on Wed, 12 Apr 2017 05:58:18 GMT]]>@constantinos
Maybe because I2C is still software implementation...

]]>https://forum.pycom.io/post/6285https://forum.pycom.io/post/6285Wed, 12 Apr 2017 05:58:18 GMT<![CDATA[Reply to WiPy LoPy I2C with ATMEGA on Wed, 12 Apr 2017 07:12:45 GMT]]>@constantinos
Have you tried lowering your I2C speed (baurate= init parameter)?

Also how long is your cable? You can try adding external pull-up (to 3.3V) resistors too (maybe 4.7K)

]]>https://forum.pycom.io/post/6292https://forum.pycom.io/post/6292Wed, 12 Apr 2017 07:12:45 GMT<![CDATA[Reply to WiPy LoPy I2C with ATMEGA on Wed, 12 Apr 2017 07:35:44 GMT]]>Are you using the Arduino libraries with your ATMEGA? If so those enable AVR's internal pull-ups too, so you have two devices enabling weak, not really up to the job, pull-ups at both ends. I guess it's very possible the bus isn't really running on spec doing that.

I don't know if you can disable the pull-ups on the Arduino or Pycom side, but maybe worth investigating.

Edit : On the Arduino side you should be able to

  digitalWrite(SDA, 0);
  digitalWrite(SCL, 0);

After calling Wire.begin to disable the pull-ups? Maybe that could help.

]]>https://forum.pycom.io/post/6293https://forum.pycom.io/post/6293Wed, 12 Apr 2017 07:35:44 GMT<![CDATA[Reply to WiPy LoPy I2C with ATMEGA on Thu, 13 Apr 2017 04:54:15 GMT]]>@jmarcelino Cables are really very short. Can't be shorter... Baud rate is 100000. I tried different baud rates but this value seems to be the correct.

I will try the pullup resistors today

]]>https://forum.pycom.io/post/6343https://forum.pycom.io/post/6343Thu, 13 Apr 2017 04:54:15 GMT