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Generic Calculator Shield for Arduino Photo-journal
03-11-2015, 07:20 PM
Post: #17
RE: Generic Calculator Shield for Arduino Photo-journal
Greetings, well, the hex, octal, decimal SPI display board is complete and operational. The driver code and a header file are provided which demonstrate how to write to the display board. The display board and firmware will display hex, octal, and decimal right-side-up or inverted. You will notice from the pics I have chosen to invert the board placing the digits near the bottom. A full schematic of the board is available. Some pics, then comment:

[Image: hex-display2.jpg] [Image: a3-schema2.jpg]

The board is a Serial Parallel Interface (SPI) board utilizing three 74HCT273 D-Type octal flip-flops cascaded to form a 24-bit shift register. Writing to any of the display units requires writing 24 bits out the dataline (one bit at a time) sending a clock-pulse (strobe) on each bit, which causes the bits to shift into the register. The benefit is that twenty-four bits (lines) can be controlled from the Arduino (or whatever) with only two lines-- strobe, and data. There is a third line (MR) master reset; it is not necessary, but does make clearing the display easier; although, since this display has an inverted LED bar, to really clear the whole display requires a 24 bit write-- which is fast.

The Arduino ino code file shows the routines I wrote to handle this display board; its header file is included for completeness.

A board like this is fun, and makes a great calculator display (think of the Wang 700c); however, for our purposes the real display will be a 16x2 LCD, but the principles are the same. Should you want to, a larger display can easily be made with more digits... just add more seven segment display chips and an equal number of 273 chips.

PS The under side of the board can be seen in a stereoscopic photo (worked over with Gimp). View the photo with the "crossed eyes" technique for a truly magnificent view. Who says only software can be 'spaghetti code' ?


Kind regards,
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RE: Generic Calculator Shield for Arduino Photo-journal - MarkHaysHarris777 - 03-11-2015 07:20 PM

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