Here I discuss about the main parts used by this project.

• 74HC595 : that's the 8-bits shift registers, 2 are required for each module so overall 50×2=100 are required for the whole project. For simplicity reasons, it is used in dump SPI mode, with no additional latch signal, because we don't care about the looks when the display is updated. On the contrary, shifting all the segments can create a cool effect for no cost !
  Stock: OK, from personal stock (a stupid display project from 2009)
• LEDs:
  - must be red/yellow/green because the forward voltage drop is lower and 2 or 3 can be wired in series. New green or blue LEDs require more than 2.5V, more resistors and more soldering...
  - 3mm is chosen because 5mm is a tiny bit too large. We have tried several models (from old stock) and chosen new diffused flat-top model with nice look and color (but slightly higher voltage drop)
  Stock: OK, bought specially for this project on eBay.
• Resistors: individual resistors require too much soldering, despite the choice of red LEDs that cuts the numbers in half. There are still 50×42=2100 resistors to solder, or 4200 joints ! I have found the solution : SIL resistors modules.
  Each display module has 84/2=42 resistors, which is not a multiple of usual SIL models so a composite method is used : 2× 10-pins SIL with 9 resistors make 18 resistors, the remaining 24 are made of 3 SIL with 9 pins and 8 resistors.
  Value has been experimentally determined to 300 Ohms
  Stock: OK, bought specially for this project on eBay.
• DIP switches : 2× standard cheap 8-switches for the data, and 1-bit switch for the mode.
  Stock: OK, bought specially for this project on eBay.

Other parts (capacitors etc.) are common and do not require a particular consideration.