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systems_glitch

7-Segment Magnified Displays

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So I got a really good deal on 230 9-digit 7-segment displays. They're the bubble-magnified sort, with 0.2" tall digits (anyone who's used an old TI calculator with LED display will remember these). I've got a few projects in mind for them, the first being a low-cost PIC based hex display, to provide direct readouts of the address and data bus on old 8-bit systems. Here's a video of my current single-character implementation:

Since I'll already have a driving structure and lookup table arrangement for the hex display project, I think I might build a serial-attached display that can be driven through either a PC serial port or a USB -> serial converter. I could mount the display in one of the unused 3.5" drive bays in my system, and have it display current CPU load, temperature, IP, et c.

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Cool... Like the 'Old School' look :-)

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Now with an array-based buffer and timer-interrupt driven multiplexing!

Using an array makes it easy to dump data from whatever into the display buffer, and the interrupt routine takes care of the rest. The first digit is a 4-glyph "spinner," the second two are displaying an 8-bit binary up count, the fourth is displaying the 8-bit count as raw segment output, and the fifth is just garbage from the uninitialized fifth byte in the buffer.

Driving the display is accomplished by connecting the segments + decimal point to the 8-bit PORTB of the PIC. The common cathodes are driven with 2N3904 NPN transistors to ground. The transistors are driven from the first 5 bits of PORTA. Due to how I have the PIC configured internally, I can only drive 5 digits at this time. The final version will be using a monster PIC18F6310, which has over 50 I/O pins in a 64-pin TQFP!

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