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tech2077′s tech blog: Running a HD44780 LCD over I2C (On the Raspberry Pi) via HaD.
One of the major problems plaguing the RasPi is the lack of GPIO, and the weird placement and random numbered GPIO pins broken out, making any code using them much more disorganized than if consecutive GPIO pins had been used. In addition to the inconvinience of using the GPIO, the LCD uses 5v, while the RasPi is strict 3.3v. In order to prevent any chance of damage to my Pi, and to solve the problem, I opted to use a PCF8574 I2C 8 bit IO expander. This makes it easy enough to use the bottom four bits of the expander for LCD data, and the next 3 bits for RS, R/W, and EN. To control the LCD this way, I wrote up a nice library to get things working on the lcd. In addition to this, I added a few extra bits to the library so that anyone can add more devices to it, and wrote a class for the tmp102 so we can have some live data to display.
Today is PiDay here at Adafruit, be sure to check out our posts, tutorials and new Raspberry Pi related products.
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lost what I had written. Anyway, most hd44780′s can accept (VCC*0.7) voltage logic input. I can control a 5v lcd with a msp430 running at 3.3v pin output. The Lcd still needs 5v, but the logic does not. Just don’t pull r/w high, don’t put it into read mode. Most people tie r/w to ground anyway.
I did use your same setup. Msp430 -> pcf8574 -> lcd. No need for level translations.
Comment by cde — June 29, 2012 @ 4:52 am