The Clock

The Clock [[Image:|200px]] What: A digital clock/timer built from our component stock Tagline: From trash to time Maintainer(s): askarel Archived: Yes

• We fried the shift register on one of the big displays.
• We need a timer for the meetings
• We need to give a purpose to the old components we have in stock

Using an Arduino for this is too easy, and we did not have one around then the project got started. I also want to combine a bunch of dirty tricks out of the cookbooks of seasoned electronic hackers:

• Power supply: 12VAC (Halogen transformer)
  • The display requires 24VDC to work -> voltage doubler
  • The CPU will require a time base -> trigger CPU interrupts using a zero-cross detection circuit on the power transformer
  • Use 32 discrete output transistors to drive the segments
• Display: 4 digits/7 segments, originally used in underground parkings.
  • Remove the fried chip
  • Replace it with a 40 pin DIP socket
  • Interface it to the custom power board using a flat cable
• System
  • Z80 based
  • Separate ROM and RAM
  • Use old EPROM as ROM software storage
  • 4x74LS373 as output buffer, 1x74LS245 as input
  • 2x74LS138 for address decoding
  • Clock generation/glue logic