Generic Calculator Shield for Arduino Photo-journal

[BarryMead]

(03-16-2015 04:59 AM)MarkHaysHarris777 Wrote:  The beauty of the Due is the 32 bit Arm core, lots of memory, fast, and a DMA controller... the bad news is that unlike the other Arduinos its a 3.3 volt system... and its not forgiving. DO NOT put more than 3.3 volts on ANY I|O pin... you've been warned. There are two opportunities for failure:1) exceed 3.3 volts on any pin, and 2) fail to provide a full logic level high on the interfacing 5v system. Both of these problems are solved by placing a voltage comparator between each I|O pin and the 5v system. I have tucked two LM339 quad comparators under the display module. I am buffering the two control lines, the four data bus lines, and the backlight driver transistor. From the second pic you can clearly see the bus, the ref voltage divider, and the I|O pullup resistors.

Mark: You can also buy 8 bidirectional level translators in a nice package from adafruit here Or for quad I2C compatible (I/O's with pullups less than 50k) level translators here