6 Digit 7 Segment SPI Display

I was bored one day so I decided to make a debugging display that can be driven by 3-wire SPI. I had a bunch of blue 7 segment LED displays and I've always got a few 74HC595s floating around so I thought what the hey. I've been using it mostly for mucking around with my new PICServo PID routine. Since the 595s have their own registers it requires no processor time. Simply clock in the digits, pulse the latch and the display changes and stays that way until a new lot of data is latched. Very handy!

As you can see it's done point-to-point on a piece of doughnut board with 0.4mm enamelled wire. I've since purchased some nice 0.25mm wire which I'm unsure if it would have made it easier since the 0.4mm holds itself in position really well. The board was actually quite easy to assemble even if the photo shows too the contrary. The 74HC595 has to be on of the best 74xxx series chips available. The outputs are pretty much all on the on side of the chip! I wish more chips were like this! Plus the 74HC595 can handle up to 100MHz clock which means no painful waiting and delays in your code (PICs aren't at 100MHz yet!) just to output to the display. My CCS compiler already has a handy driver for the 74HC595 included so interfacing was a matter of three #defines, plus just bit-banging the pins isn't exactly hard either. Heck, I debugged it originally with a de-bounced button and a few dip switches. :)

I originally built this display that ChaN uses, but I was a little under whelmed. This was mostly because as a debug display the micro-controller was having to spending more than 85% of it's time refreshing the display fast enough to make all eight digits bright enough to be practical. I used the built display for a while until I tore it apart to make something else. This photo must be a fairly long exposure or that micro-controller is spinning a lot of cycles to get the display that bright! :)

My next thing is to make a custom perspex front and back panel for it on the little WidgitMaster CNC machine. Then it will look the business. :)