Ever wanted to use any pair of pins for I2C on Arduino, not just the dedicated pins on Analog 4 & 5? Me too, so I made a quick little Arduino library called “SoftI2CMaster”, available in the “blinkm-projects” Googlecode repository.
Get it here: SoftI2CMaster.h, SoftI2CMaster.cpp.
It’s still a work in progress, but it can write data pretty successfully and do it over longer cables than normal.
For the VIMBY/Scion Hackerspace Challenge, I created an array of BlinkM MaxM-powered accent lights for the device we made. Because the I2C cable was longer than a few feet, the normal Wire library that BlinkM_funcs.h uses to communicate with BlinkMs couldn’t be used. This is because the Wire library assumes a perfect bus. If there is any noise or other bus problems, the Wire library will currently lock up. For the SoftI2CMaster library, I wanted it to be very tolerant, even lazy, about bus problems and also have more tunable timing to let you slow the bus down. Of course, you still need pull-up resistors on the two lines. I’ve found using 2.2k resistors to be good.
The SoftI2CMaster API follows Wire’s API pretty closely:
- SoftI2CMaster(sdaPin,sclPin) — create an new SoftI2CMaster for the two pins specified
- beginTransmission(address) — begin sending data
- send(data) — send some data (byte or byte arrays)
- endTransmission() — stop sending data
In use it looks something like this:
There is a simple demo for BlinkMs that this library currently lives in. It’s called “BlinkMSoftI2CDemo” and shows off a simplified BlinkM_funcs called “BlinkM_funcs_soft.h“. The entirely of BlinkMSoftI2CDemo is shown below.
