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8 Channel D/I Card for RS232

8 Channel D/I Card for RS232
This project is a card with eight optically isolated TTL-compatible inputs for external connection to the serial port, which communicates through the RS-232 protocol. On this card you will look in vain for a UART or microcontroller chip because the design is based on a 27C256 EPROM.Each digital input is connected to an optocoupler (IC7-IC14) through a resistor (R2-R9), and drives it with a current of 5 mA when the input voltage is 5 Vdc.
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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 = 10k? 8-way SIL array
R2-R9 = 1k?
R10,R12 = 10k?
R11 = 4k?7
P1 = 25k? preset H
C1 = 100pF
C2-C5,C11 = 100nF
C6-C10 = 10 µF radial
C12 = 330nF
D1-D8 = 1N4148
D9 = 1N4001
IC1 = 4060
IC2 = 4040
IC3 = 27C256 (see text for programming)
IC4 = 74HC151
IC5 = MAX232
IC6 = 7805
IC7-IC14 = 4N28 of CNY17-2
K1-K8 = 2-way PCB terminal block, raster 5mm
K9 = 9-way sub-D socket (female), PCB mount
S1 = 8-way DIP switch
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