Article

COM Port Tester

With 3 LEDs and 4 switches

The serial port (often called the COM port) is perfect for connecting various electronic circuits to the PC. The complexity of the connected circuit varies from a few I/O lines to control something and read the state of switches, to a complex communications system between several computers. This circuit is in the first category and uses the serial port to perform a few simple I/O tasks.The COM Port Tester is a simple circuit that shows how the signals on a serial port can be used to control another electronic circuit. We will have to disappoint those of you who expect to use the serial port to control motors and lights etc. This circuit is limited to driving three LEDs and reading the state of four switches, nothing more and nothing less.

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Materials

020370-PCB.pdf

020388-11.zip

Gerber file

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

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PCB

Download Gerber file: 020370-1.zip

Component list

Resistors:
R1,R2,R3 = 2k?2
R4-R8 = 10k?
Semiconductors:
D1 = LED, 3mm, green, low-current
D2 = LED, 3mm, yellow, low-current
D3 = LED, 3mm, red, low-current
Miscellaneous:
K1 = 9-way sub-D socket (female), angled pins, PCB mount
S1-S5 = slide switch or rocker switch, 1 make contact
9-V battery with clip-on leads
PCB, available from The PCBShop
Disk, project software, order code 020388-11