The interfacing hardware has been changed somewhat with the moving from Basic Stamps to the Propeller chip. The new circuits take advantage of the higher performance of the Propeller chip and some of the functions have been moved to software. The turnout drivers are improved to minimize external parts and provide an additional measure of protection to the switch machine coils. The DCC only block detectors use a different transformer isolation circuit to minimize parts and eliminate the need for the high current diodes. The inputs and outputs are interfaced using serial/parallel shift registers. This is one of the areas where the higher performance of the Propeller chip makes this easier to accomplish. The power supply circuit now includes a 3.3 volt output but is essentially unchanged from the Basic Stamp version.

The Propeller P8X32A-Q44 ProtoBoard (Q1 2007 availablity) will be used. This board is expected to contain the following components.

• Surface-mounted P8X32A-Q44 Processor, socketed crystal clock
• 64k EEPROM with SDA and SCL lines routed to where they can be accessed. Pullup resistor on SCL if no compatibility issues
• Power light with three-position switch (0 = off, 1 = power to all supplies except a few servo ports, 2 = power to all places)
• 3 x 4 inch size with mounting holes the same as the BOE, Super Carrier, and SX Proto Boards
• Dual power supply: 5V, 3.3V, and Vss
• Two (2) 47 uF capacitors across the 5V power supply for servo management
• Friendly power rails along the edge of the board for multiple connection points
• Several rows of connected 0.1" pads for easy point-to-point soldering, providing 1x2 or 1x3 connections
• (4) 3-pin locations for servo connections, or other 3-pin devices made by Parallax (serial LCDs, Ping, PIR, etc), and a jumper to supply these ports with Vin or Vdd. 
• Ample through-hole area for additional user circuits
• Strain-relief holes for wires leading off the board
• PropPlug programming connection
• USB2SER programming holes. Use of this method of programming requires desoldering of the PropPlug programming header and resoldering it into the 4 holes for the USB2SER.
• Unpopulated dual ps/2 and VGA. We are looking into using NorComp 999-H15-PS2-571 which is a dual PS/2 with a VGA plug stacked on top.
• 4 A/D ports near the Propeller, we may have it so these are capable of being disabled to regain the I/O pins 
• No breadboard (however there will be enough space for the user to place one over the prototype area).

Use the following links to view the circuits on each schematic sheet.

Propeller Circuits
Solenoid Switch Machine Driver Circuits
Input Sensor Circuits
LED Driver Circuits
Keypad and Button Interface Circuits
Power Supply Circuits

Propeller Control Electronics:   Overview   Flow Charts   Program Code   Schematics   Photos
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Copyright © 2006 Don Buczynski
San Diego, California