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A project log for Tetradeca - 1KB - 3 games on 14seg displays

Three games on a PIC16F1705 \with eight 14- segment displays and a discrete diodes character ROM

matsengmatseng 01/06/2017 at 03:055 Comments

Since I soldered this on perfboard instead of on a real made pcb I didn't bother to draw the schematics in a PCB CAD package. So my hand-drawn scribbles will have to do.

Only the first three characters are shown in the diode-ROM, but all of them are documented in the code.

Discussions

matseng wrote 01/06/2017 at 14:46 point

I see that I've forgot to add the 14 LED current limiting resistors put between the display cathodes and the collectors of the segment driver transistors to the schematics.

I do actually have 220 ohm resistors there or else the displays would be very unhappy being driven to 5 volt vcc by a p-fet and to ground via a fully saturated small signal BJT.  There probably would have been 100+ mA thru each segment...

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matseng wrote 01/06/2017 at 05:13 point

heh....  strange that you haven't seen the '595 before. In almost ashamed to use it since it's by far the most commonly used ic in the "arduino maker" community. ;-)

I'm doing basically that. But I've set the /OE permanently low (active) so they are always outputting data. But the outputs doesn't update until the latch signal gets a rising edge.

My original plan was to use 3-to-8 decoders, but the only ones I would locally was the '138 with inverted outputs, and that won't work unless I use Schottky's or the transistors will never be fully turned off making all segments glow faintly all the time.

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Eric Hertz wrote 01/06/2017 at 11:22 point

That made me laugh. Glad I'm not the only one with a '595 aversion ;)

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Ted Yapo wrote 01/06/2017 at 12:39 point

I'm from the pre-arduino/maker CD4017 days of simple port-expansion.  I even got a tube of those new-fangled 74HC4017's which go faster :)  If you use one of those, it's shameful *and* it gives away your age :-)

I always get stumped by the '138, too, unless it's used for an active low line (like inverted 3-state output enables for addressing things onto a bus).

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Ted Yapo wrote 01/06/2017 at 03:11 point

Hmmm.  I hadn't seen the 74HC595 before.  Interesting part. You shift in a single high-bit to activate one of the columns, and only enable the output when the bit gets to the correct position?

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