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• The Project

  Last updates
  January 18th 2005 : I have received the 4.9152Mhz crystals. It's the perfect frequency! I can generate a multitude of practical baud rates from 19200bps to 150bps. Good thing cause I have lots of them!
  January 17th 2005 : I now have an almost functional input circuit and a complete schematic is now online.
  
  I wanted to have a nice and simple way of interfacing with the computer from my bedroom. There is already Cat5e cable all around the place so I could use that for communication. I bought some VFDs (Vacuum Fluorescent Display) on eBay. These are nice because they are brighter than LCDs (as characters emit their own light) they also have parallel and serial ports and include an onboard inverter so all you need is regulated 5v. I will be using a Parallax 4x4 matrix keypad for input. Note that I'm neither an electrical egineer neither a great software developer so there might be some mistakes around in the schematics and source codes. That's not including all those that I have already fixed and that have brought me where I stand today.
  
  By the way, it all started when I saw this project by James Sentman.
  
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• The Hardware

  

  
  In short this is how the circuit works.
  
  The MAX232 converts RS232 data (±12v) to (±5v). Tx Data from the computer is then sent directly to the VFDs. As for inputs, when the 74C922 16 Key Encoder detects a key was pressed on the keypad, it converts this number as a 4bits integer and adds it to ther 6402 UART's buffer. The word is then sent to the serial RxD via the MAX232. The 74HC4060 14 Stage binary counter is used to generate a proper clock frequency from the crystal for the UART. It is also notable that you could use this circuit (apart from a few differences) to drive parallel LCDs and devices!
  
  Be creative :D
  
  As I said previously, the 74HC4060 and the crystal are used to generate the proper baud rates for the UART. The 4.9152Mhz XTAL (5Mhz would do just fine, but I could get the more precise one) is great as it generates practical baud rates from 19200Bps down to 300Bps, once it's been down clocked by the 74HC4060. These baud rates match perfectly with those from the VFD so running both on the same line is no problem.

  VFD and keypad input to RS232 circuit.

  I grabbed the original on BeyondLogic. Specs are modified accordingly.
  

  You can't see it on the schematic but pins 1 to 4 of JP3 (the keyboard connector) are inverted from IC4's pins.
  
  The keypad is a 4x4 matrix from parallax. It is rather expensive but I couldn't find anything from surplus or to scavenge with the proper specs and form factor. Another advantage of have one 4bits taken by the keypad is that you have another 4bits for various inputs. One could easily add another 74C922 and have an extra 16 inputs!

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  In the above picture you can see the VFD displaying iTunes info as well as the date.
  The data is scrollen on the VFD to be able to display full track names and id3tags.
  
  
  Here you can see one of the implemented modules. The pager will allow for quick messages.
  Messages are shown with the appropriate command. The alert message flashes to attract attention.

  You can't see it, but the display sits in a plexi case. Make sure you never leave the VFDs to the open air. It contains a high voltage inverter and also seems to be fairly picky on static (I've fried one already). The display is connect straight to the serial port (on a Keyspan USB to Serial adaptor). As shown above the MAX232 is used to bring serial communication to TTL levels. The VFD could run on parallel to, but it was not practical in this case. This required a serial to parallel UART and was much more complicated. Although, I will still need this circuit for the keypad as it is decoded to parallel. Doing things this way saves a bit on parts and mostly on soldering time as it would add around 10 connections. It also means I could have the VFDs a bit further away from the keypad. I'd like to find a flexible metal neck table lamp for the VFD, make it more retro than it already is.
  
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• VFDWork

  VFDWork is a utility for creating custom chars on the VFD as well as managing options such as brightness, cursor mode, etc. It is bilt in REALbasic. You can download it here, or you can build it yourself by getting the source.
  
  

  
  
  
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• VFDriver

  You can grab a recent snapshot of the source code here. It should work on any POSIX system (if you remove the utf2ascii conversion), just make sure you set the serial port using the proper tty name. This is my first C program so bare with me. I intend on adding different modules (weather, email, etc) in the future. The program currently reads status commands from a text file. This will be replaced by serial input when I finish the keypad circuit.
  Thanks to Spike for helping out, a lot, with the code.
  

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