Technical Projects








Board Fabrication  

Because almost all of the components are SMT, a printed circuitboard is necessary for prototyping the design. The board was layed out and hand-routed (!) using CADSoft's EagleCAD. EagleCAD is a freeware PCB-design software that runs on linux and windows and can easily export Gerber files. An additional library is necessary for the CS8900 chip and the isolation transformer. Board rev. 1 was printed by AP circuits, using their rapid prototyping service. The board can be easily adapted to use the free drills and does not have excessive vias.

Component Acquisition  

Almost all of the components required are obtainable from Digikey or some other components supplier. The CS8900A and the isolation transformer are somewhat more difficult. A search on FindChips or similar may reveal a stockist. The following parts are pin compatible with the transformer:

  • Vitec Corp #46Z248 SMD Isolation Transformer
  • Bel Fuse Inc #S553-0716-00 SMT 10BASE-T Single Port Transformer Module
  • Halo Electronics Inc. #TG42-1406N1 SMD 10BASE-T SOIC Isolation Modules
  • Valor #ST7011 or #ST7010
Make sure to check the datasheet to make sure you're getting the right transformation ratio, and SOIC outline! They run $5-$10. The CS8900A is $10-$15. Sometimes samples can be obtained from the companies in question.

All of the capacitors, LEDs and resistors are 1206 sized, and relatively inexpensive. The 4.99K resistor must be 1%, but all of the other values are 5%. The crystal package is quite pricey, at $6, and can be exchanged for any oscillator desired. Per board cost for components should be around $30.

Board Stuffing  

Actually soldering the components is a non-trivial task...