My cousin often gets a hold of some old electronic devices that are very suitable for tinkering around. For a few we've managed to find the specifications online and been able to hook them into the PC's parallel port. The results are sometimes unexpected. 


I remember this came off from some old telephone or something. It's a HD44780 character display that has a builtin ROM font as well as the capability to show a few programmable characters. The software I wrote shows data from Winamp and Motherboard Monitor 5 (memory consumption, CPU usage, temperatures, whatever MBM is capable of tracking).


The wiring is not that difficult to do, except that it needs a +5V to hook into. These sources give more information:

How to control a HD44780-based Character-LCD

HD44780 Commands

Ok, such a small character display doesn't really feel that cool nowadays. A lot neater display we managed to control through the LPT port was the display found from Nokia 3210 mobile phones. The controller is a PCD8544 chip and the display has a monochrome 84x48 pixel resolution.


This was some serious business, since we now could show animation as well. Also, a really cool trick that is heavily used on the TI graphing calculator games community is to simulate grayscale colors by quickly flickering the leds between on and off states. The technique turned out to be really smooth on this display and you can distinguish as many as 8-10 different levels of gray.


The most difficult LPT project however was to get readings from these 1-Wire DS1820 thermal sensors manufactured by Dallas Semiconductor. The biggest problem was that XP thread scheduling interfered too much with microsecond-critical IO timing. Luckily the DS1820 has good CRC features and the erroneous samples could be filtered out.


Last Updated (Thursday, 01 May 2008 12:28)