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Precision Measurement Central (4)

RS485, or networking the MSC1210 micro

Precision Measurement Central (4)
The RS485 port on the MSC1210 board provides great opportunities for communication with other systems. For example, it allows a number of MSC1210 boards to be connected up into a network and talk to one another over distances of several kilometres.This fourth instalment in the series on the MSC1210-based Precision Measurement Central (kicked off in the July/August 2003 issue) is entirely devoted to the RS485 interface. This month we will cover the theory and hardware. The December 2003 issue, finally, will discuss the practical use of the RS485 interface in a small project that goes to show how up to 255 MSC1210 boards can communicate with a single PC through an RS485 link. The converter required for the job is discussed in this article instalment.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor 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.

Resistors:
R1 = 220k?
R2 = 22k?
R3,R4 = 560?
R5 = 120?
R6,R7 = 1k?
R8,R9 = 47?
Capacitors:
C1,C3,C5,C6,C11 = 10µF 16V radial
C2,C7,C8,C9,C12 = 100nF
C4 = 220nF (10% tolerance)
C10 = 10µF 35V radial
Semiconductors:
D1 = 1N4001 (DO41 case)
D2,D3 = 9V1 zener diode
D4,D5 = 4V7 zener diode
D6 = LED, low current, green, 3mm
D7 = LED, low current, red, 3mm
IC1 = MAX232 (DIL case)
IC2 = LTC485 or MAX487E (ESD/EMI-optimised) (DIL case)
IC3 = 7805 (TO220 case)
IC4 = 74HCT123 (DIL case) (Philips preferred)
Miscellaneous:
K1 = 9-way sub-D socket, PCB mount, angled pins
K2 = 4-way PCB terminal block, 5mm lead pitch
S1 = 4-way DIL switch
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