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8 Channel D/O Card for RS232

8 Channel D/O Card for RS232
This article describes a card with 8 open-collector digital outputs for external connection to a PC serial port. The design of this card is based on direct accessing of the PC’s UART registers to adapt the communication from serial to parallel.A computer may have one to four serial ports (COM1 to COM4) where each port occupies eight locations on its memory map as shown in Table 1.
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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,R2,R3 = 2k?2
R4,R5,R6 = 10k?
R7-R14 = 1k?
Capacitors:
C1,C2,C3 = 100nF
C4 = 330nF
Semiconductors:
D1,D2,D3 = 1N4148
D4-D11 = LED, high efficiency
D12 = 1N4001
IC1 = 4040
IC2 = 74HC573
IC3 = 74HC541
IC4 = ULN2803
IC5 = 7805
IC6,IC7,IC8 = 4N28 or CNY17-2
Miscellaneous:
K1 = 25-way sub-D socket (female), PCB mount
12 solder pins
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