Circuit Boards




The Interoffice Signal System was designed to have 8 lights and 8 buttons to relay 8 signals. Aerie Dental Centre required 9 terminals spread throughout the office. The office was set up to have a star topology. To elaborate, all conduit in the office going to the operatories and rooms converged to one central area. All nodes will be terminated at a terminal strip in this location. 


To make the assembly compact and versatile, a microcontroller was used. The ATMEL AVR AT90S4433 8 MHz 8-bit RISC Microcontroller featured  UART and the ability to drive the LEDs directly. See Microcontroller for further details.  


The RS-485 standard over twisted pair was chosen for communication between terminals. A MAXIM MAX483 TTL to RS-485 driver converted the UART outputs of the ATMEL to RS-485. Refer to RS-485 for a more detailed explanation. Two solutions for the twisted pair cable were found.  2-Pair 22AWG CSA Type MPG/CMG IBM cable or 3-Pair 26AWG Category 3. The two pairs of the category 3 would be used for power and ground to increase ampacity. Both are common and inexpensive.


Refer to Components for the components used.


Printed Circuit Boards were designed then printed at a board house. Refer to Circuit Boards for further details.


The total costs in parts and boards for each terminal was $69.31. 








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Last modified: August 04, 2001