About the article


RS485 home network with a maximum of 64 terminals

This universal bus has many applications. With a PC as a master, information can be exchanged with up to 64 slave terminals. Because each terminal contains eight selectable inputs and outputs as well as an LCD, this home network is not only suitable for use in the home, but it would also be perfect as a combined alarm/communication system for schools and small firms.Before we delve into the technical details, we will first give a brief description of the system.The backbone of the system is a complete serial bus that uses its own protocol. Data is sent to and received from a maximum of 64 terminals over long distances using an RS485 interface.The hardware of the system consists of a simple RS232 to RS485 converter and a microprocessor driven terminal. Of the latter you will obviously need to build as many as are required. The software consists of a program for the PC and one for the ‘terminal processor’.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Component list
R1,R3 = 470?
R2 = 120?
R4 = 100?
C1,C2 = 100nF
C3-C8 = 10µF 50V radial
D1 = 1N4001
IC1 = MAX232
IC2 = 7805
IC3 = SN75LBC184 (or 75176)
JP1,JP2,JP3 = 2-way pinheader w. jumper
K1 = 9-way sub-D socket (female), PCB mount, angled pins
K2 = 9-way sub-D plug (male), PCB mount, angled pins
PCB, order code 010113-1
R1,R6 = 8-way SIL resistor array, 10k?
R2-R5 = 1k?
R7 = 8-way SIL resistor array, 1k?
R8,R9 = 470?
R10 = 120?
R11 = 100?
P1 = 10k? preset H
C1 = 1µF 16V radial
C2,C5,C7,C9-C12 = 100nF
C3,C4 = 15pF
C6 = 10µF 16V
C8 = 100µF 25V
D1-D12 = LED, red, rectangular, high efficiency
D13 = 1N4001
IC1 = 4021
IC2 = AT90S8515-8PC programmed, order code 010113-41
IC3 = TL7705-ACP
IC4 = SN75LBC184 (or 75176)
IC5 = 7805
JP1,JP2,JP3 = 2-way pinheader w. jumper
K1, K2 = 10way pinheader
K3 = 9-way sub-D plug (male), PCB mount, angled pins
K4 = 9-way sub-D socket (female), PCB mount, angled pins
K5 = 14-way boxheader
K6 = 2-way PCB terminal block, lead pitch 5mm
S1 = 8-way DIP switch
X1 = 3.6864MHz quartz crystal
LCD module: 2 x 20 characters
PCB, order code 010113-2
Disk, contains PC en controller software (incl. source code files), order code 010113-11
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