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RS232 In-Line Data Spy

instant analysis of serial links

RS232 In-Line Data Spy
With the help of a minimal quantity of hardware and a simple piece of software it is possible to tap into the data stream between two serial interfaces and observe it on the computer monitor.The name ‘Data Spy’ immediately conjures up images of clandestine practices, in general however, the circuit described here will not be used for such purposes. There are many legitimate reasons for analysing the data stream between a PC and a peripheral, or a second PC. It could be part of a faultfinding procedure, for example, or as a continuous data monitor, or as an educational exercise to unravel the details of certain protocols.The implementation of the circuit described here is a kind of in-line plug that is simply inserted in series with the connection between the RS232 interfaces of the PC and the peripheral under consideration. A third sub-D connector functions as the connection for the additional PC, which is used to examine the data stream.
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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.

R1-R4 = 15kOhm
C1 = 10µ F 25V radial
C2 = 100nF
D1-D4 = 1N4148
IC1 = 4011
K1 = 9-way sub-D plug (male), PCB mount
K2,K3 = 9-way sub-D socket (female), PCB mount
JP1, JP2 = jumper
PCB, order code 010041-1
Project software: code 010041-11, free download
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