Sunday, July 11, 2010

Vacuum Florescent Display

I picked up one of these displays yesterday at SkyCraft. Someone was nice enough to create a documentation page for them, and has a youtube video example...

Vacuum Florescent Display - TechNet


After reading the documentation above, I got out a DB9 serial cable and wrote some quick Processing code to test out the VFD. It worked according to spec and I had it cycle through the character sets (including an undocumented third set). Reading deeper into the docs above, I saw the comment about RS-232 to TTL conversion by an onboard IC. Feeling newly empowered by knowledge and tools, I got out the logic analyzer and found the pins that had the TTL serial feeding the display microcontroller. Once I confirmed the pin, I looked for an open test pad to solder to - no such luck. I downloaded the datasheet for the microcontroller, found the rx pin, attached the analyzer and confirmed it had the TTL serial signal. This time, there was an open test pad, I confirmed it had TTL serial, and then soldered a jumper wire from the test pad over to one of the unused pins on the main connector. I got out an Arduino, quickly ported my code from Processing to Arduino and had the same character set scroller running from the Arduino.

So what's ironic is that today I set out to connect this display to an Arduino by building a MAX232 circuit that would convert the Arduino TTL serial to RS-232. I had ordered the wrong capacitors and couldn't build the circuit - but then later in the day, determined the reverse conversion was happening on the VFD and I could just cut out the middle man. I'm no longer upset about ordering the wrong caps - this was a WAY better learning adventure with a better outcome. Learning is fun :)

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