Arduino I2C with Wire Library Transmission Speed

When working with the Arduino I2C protocol using the Wire library, transmission speed is an important consideration. Unfortunately, measuring frequency at the SDA and SCL pins can be a challenge without the right equipment. In my case, I was unable to find a signal to measure frequency using my digital multimeter (DMM). Despite this, I did notice that changing the transmission speed from 'fast' to 'slow' didn't seem to affect the performance of Adafruit's MCP4725 sketches.

After some troubleshooting, I discovered that the issue lay with the Wire library itself. Specifically, the `wire` variable was not declared in scope, which caused errors when trying to use functions like `twowire.begin()` and `twowire.begin(fast)`. By modifying the i2c and wire libraries to include the necessary declarations, I was able to get my code compiling without errors.

In addition to fixing the library issues, I also discovered a bug in Adafruit's MCP4725 DAC breakout library. The problem lay with the `i2c_openadapter()` function, which should be defined as `int i2c_openadapter(bool i2c_speed)` instead of just `void i2c_openadapter(void)`. This change needed to be made in both the i2c.c and i2c.h files.

By making these changes, I was able to successfully use the Wire library with my Arduino board to transmit data over I2C at different speeds. One important tip is to take advantage of the IDE's compile window scroll-up feature, which can provide more detailed error messages that can help troubleshoot issues.

Overall, working with the Arduino I2C protocol using the Wire library requires attention to detail and a willingness to dig into the code to fix issues. With patience and persistence, it is possible to achieve reliable communication over I2C at various transmission speeds.

Arduino i2c with wire library transmission speed