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I2C Interface for RS232 Port

new lease of life for the COM Port

I2C Interface for RS232 Port
Back in October 2000 we described a versatile I2C bus interface that plugged into the PC printer port. Nowadays the PC serial port is rarely used for keyboard or mouse connection so it’s sensible to make better use of it. This design provides an I2C bus connection to the PC’s serial port.From a hardware point of view this serial port version of an I2C interface card could hardly be simpler. Looking at the circuit diagram (Figure 1) it can be seen that the MAX232 chip (IC1) is the main component of the circuit. This IC translates the signal voltage levels on the I2C bus to RS232 voltage levels that can used by the serial COM port of a PC. Even Notebooks that are notoriously fussy about serial port signal levels will work happily with this interface.The 9-way RS232 connector K1 that connects to the serial port of the PC has its DCD wire (pin 1) connected to the DSR wire (pin 6). The port driver software will check this connection during initialisation to determine if the interface card is present.
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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-R4 = 10kOhm
R5 = 1kOhm
Capacitors:
C1-C4,C6 = 10µ F 16V radial
C5,C7,C8 = 100nF
Semiconductors:
D1 = LED, red, high efficiency
IC1 = MAX232
IC2 = 74LS06
IC3 = 7805
Miscellaneous:
K1 = 9-way Sub-D-socket (female), PCB mount, angled pins
K2 = 6-way Mini-DIN socket, pins at 240 degrees, PCB mount
PC1,PC2 = solder pins
JP1 = 2-way pinheader with jumper
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