pcbdesign - rosco-pc/propeller-wiki GitHub Wiki

This page is under construction. It is intended to contain information for people designing printed circuit boards for the Propeller.

Currently a lot of placeholder text and links to forum threads. Will be summarizing info from threads as time goes by.

This page is primarily maintained by mpark, but anyone is welcome to make improvements.

Propeller chips

  • Connect all Vdd and Vss. Floating Vdd or Vss pins may cause PLL failure [citation needed].
  • "What destroys the PLL (actually, the logic circuits downstream from the PLL) is high current running between VDD or VSS pins. Those pins need to be tied together very closely on the PCB. As Leon said, good PCB layout is critical. Bad PCB layout can not only cause caps to be ineffective, but give current the opportunity to flow between VDD or VSS pins, which can damage the Propeller. The key is to keep things very tight. Make power routing your first priority in a PCB design. Make power traces as short as physically possible, and at least 15 or 20 mils wide."—Chip Gracey http://forums.parallaxinc.com/forums/default.aspx?f=25&m=410277
  • Best practice Power/Ground on Propeller Chip
  • Connection of RESn Pin
  • Pins 30/31

Crystal

  • The Propeller specs call for a parallel-resonant crystal with about a 20pF load capacitance (for 5MHz). If you were to substitute a series-resonant crystal or one with the wrong load capacitance, you might well see a frequency discrepancy.*
  • crystal considerations thread
  • 5MHz quartz with small housing required (Note: If using small watch crystal, clean out any flux or other gunk between the closely-spaced pads. Cautionary tale: [What's wrong with my PCB? re-resolved])

EEPROM

  • The Prop has to have an EEPROM with at least 32K bytes of storage like the AT24C256 or Microchip 24LC256. If you need to store any significant amount of data or another program (overlay), you'd need an AT24C512 or Microchip 24LC512 or possibly an AT24C1024B or Microchip 24LC1025.
  • Alternative: replace the eeprom with a ramtron FM31L278 device; you will have the same boot-eeprom capability (32K-unlimited writes) plus a real-time clock.*

Bypass/decoupling caps

  • You need one 0.1uF ceramic bypass cap next to each Vdd/Vss pair.
  • Design rules for stable propeller operation and overclocking
  • decoupling caps on the prop. If you plan to socket the Propeller, you can fit them under the propeller, that lets you get them really close to the power supply pins. I'd do one for each side. 0.1 uf or so. I've found that Machine pin 40 pin dip sockets give you the room, the cheap sockets put a reinforcement rib right across the center, blocking the area I normally put them. My point? look at the socket you plan to use before laying out the board, or you may find problems when you decide to solder them together.
  • about decoupling caps ... put down some 1208 or 806 smd device pads with short fat traces. There is nothing on the back so a ground plane would be nice there and will make the fab easier to spin. If it was my board I would allow a provision for putting smd resistors in series with all propeller traces.
  • Decoupling caps, the magic component

Power

General

Surface mount

PCB fabrication houses

Advanced Circuits in Colorado*
BatchPCB "is the cheapest place but it does take some time to get the boards back (they are actually made in China)"; "Nuts and volts uses a service called batch pcb I think. They take small orders until they have enough for a panel and then run it. The turnaround time varies but the price is reasonable."*; "I don't think it is Nuts and Volts that's directly affiliated with Batch PCB, I think it is www.sparkfun.com. If you have a lot of boards that add up to one or more panels, then Batch PCB can turn around fairly fast. I believe Batch PCB uses Gold Phoenex for the actual fab." *
ExpressPCB
http://www.futurlec.com/PCBService.shtml "They have an automated quote generator on-line. Reasonable prices, fast turn-around, low cost World wide shipping available.*
Gold Phoenix in China; "If you need large panels"*
PCBexpress
SeeedStudio in China; "has a nice PCB service and can even partner with the designer to distribute an open hardware "product" through their online store. Low cost International shipping with tracking via Hong Kong." *

Related thread: Best Method for "short run" of PCBs

PCB design software

You forgot to mention the best (IMHO), free (GPL), cross platform (MAC too) suite of programs for EDA (Electronic Design Automation), KiCAD. KiCAD has Schematic capture, PCB layout editor, Gerber viewer, footprint selector, footprint editor. autorouter, project manager, etc.; a complete suite capable of producing professional quality layouts..

iut-tice.ujf-grenoble.fr/kicad/

kicad.sourceforge.net/wiki/index.php/Main_Page

There's a large (2,5k member) active KiCad Yahoo Group here:

tech.groups.yahoo.com/group/kicad-users/

Parallax approved Eagle parts

Propeller Schematic Symbols for Express PCB

There is an excellent Homebrew PCB Yahoo Group with almost 5k members. Much help on EDA and fabricating your own PCBs:

tech.groups.yahoo.com/group/Homebrew_PCBs/

Photoboards: They really need testing. Exposure time varies from manufacturer to manufacturer (and with the kind of paper or transparency you have), and developing too.*

Common numbers

  • Reminder: Units: Parts come in imperial and metric sizes, sadly. When you give size it would be useful to have both for example: 50 mils (1.27mm), or 1.27 mm (0.05"). Or something similar.
  • standard via size?
  • I'd make your prop plug via's (holes) 1.02 mm or so - the standard size is just too small for a standard header.
  • demo board pinouts
  • protoboard dimensions
  • DIP pin spacing

Members' boards

Other threads of interest

Rayman's PCB page