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
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
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.
to Components for the components
Circuit Boards were designed then printed at a board house. Refer
to Circuit Boards for further
total costs in parts and boards for each terminal was