Control an LED via USB/RS232 adapter

Today I lighted an LED using my USB to serial adapter. Here is how it looks:

Here is how it works:

• Connect your USB to serial adapter to your computer.
• Find out what device name it got using dmesg:

[29231.270163] usb 2-1.6: pl2303 converter now attached to ttyUSB0

in this case it is /dev/ttyUSB0

• Find out which pin is TXD and which is GND. PIN 3 is TXD and PIN 5 is GND.
• Write a small python program to switch on the TXD pin on the respective device:

import serial, time
conn = serial.Serial('/dev/ttyUSB0',
                    baudrate=9600,
                    bytesize=serial.EIGHTBITS,
                    parity=serial.PARITY_NONE,
                    stopbits=serial.STOPBITS_ONE,
                    timeout=1,
                    xonxoff=0,
                    rtscts=0)
conn.setBreak(True) 

• know that you can probably hold an LED directly to the pins as they should contain current limiters.
• know that PIN 5 holds 0V and all other PINs hold 0V or +5V usually
• So risk it and hold the long pin (plus) to PIN 3 and the short one to PIN 5

Why does this work? Because there is a limiter that limits the power so the LED does not break. If I connect RI and TXD then via an LED it shines, plus RI's state, read by python, turns from off to on.

See also

• programming electronics