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VGATonic Goes on a Diet

A project log for VGA Graphics Over SPI and Serial - VGATonic

640x480 (and 848x480!) Color VGA Video Card for Microcontrollers and Single Board Computers

PKPK 08/30/2015 at 17:210 Comments

I just built 2 boards from a new batch of VGATonics I sent to OshPark: this one is 39.1% smaller, roughly 5.5 square inches versus roughly 9 for the old one:

Sure, the RCA jack is gone on this version (but not forgotten - on the back side of the board there is a 32 pin .4mm pitch exposed area to add a Hirose connector if I want it and the other GPIOs), but I'll be experimenting a bit with the software on this version.

I put an Atmel ATTiny 4313a in place of the 2313a (they are pin compatible), and added an external 8 MHz crystal - my plan is to make the Asynchronous Serial a bit more robust and allow some more speeds. In the interest of signal integrity, I shielded 70% of the external SPI signal lengths on the board (although, of course, most of the SPI signal integrity problems I've seen were due to long, untwisted jumpers) and made 3 'separate' ground domains. Finally, I fixed the swapped MOSI/MISO on rev A which caused me to have to use software SPI to program the clock - it's all hardware SPI now from the ATTiny!

Minor details all, but it should add up to more stable VGA from this revision - along with some enhancements on the Asynchronous Serial side.

Also, my daughter really likes that I added LEDs - although I should have used something bigger than 0603s! (Orienting those things is painful). It took me about 4 hours to solder and get both boards working that you see above - bringing VGATonic's family size to 8 counting the 4 down in Pasadena!

I have it 'working', but with minor edits the old firmware - when I get the external crystal working with a few more serial speeds I'll post everything you need to build rev B. This will eliminate the optional calibration step from the build instructions when done. For now, if you build one, please build Rev A.

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