Blink a LED lamp (toggle) with the DTR pin of a Linux Serial Port (such as /dev/ttyUSB0)

This code toggles the DTR pin of a Linux serial port (such as /dev/ttyUSB0).

It blinks a cheap LED lamp usually powered by 3xAAA 1.5V batteries, so it could be powered over USB 5V.

Compile

zoobab@sabayonx86-64 /home/zoobab/soft/toggledtr [55]$ make clean
rm -v toggledtr
removed ‘toggledtr’
zoobab@sabayonx86-64 /home/zoobab/soft/toggledtr [56]$ make
gcc -o toggledtr toggledtr.c
zoobab@sabayonx86-64 /home/zoobab/soft/toggledtr [57]$ 

Run

zoobab@sabayonx86-64 /home/zoobab/soft/toggledtr [323]$ sudo ./toggledtr 
ttyUSB0 opened successfully
DTR = 1
DTR = 0
DTR = 1
DTR = 0
DTR = 1
DTR = 0
DTR = 1
DTR = 0
^C
zoobab@sabayonx86-64 /home/zoobab/soft/toggledtr [324]$ 

Note the CTRL-C at the end to quit the program loop.

Photos

The Minus sign of your batteries (-) is connected to GND, and the Plus sign of the batteries (+) is connected to the DTR pin. When the DTR pin is HIGH, there is current on the lamp, when DTR pin is LOW, there is no current flowing.

About the lamp

The LED lamp "Lampe retro LED sur tirette" was bought for 2EUR on the 13 February 2016 at Action.be in Brussels.

Product page is here:

http://www.action.be/fr/lampe-r-tro-led-sur-tirette-div-couleurs

Product picture:

https://raw.githubusercontent.com/zoobab/toggledtr/master/retro-lampe-led-tirette.png

About the USB serial adaptor

The CP2102 adaptor has the DTR pin exposed on the last pin of its header, NoSolderingRequired(tm):

Credits

This is a fork of the well documented code of Xanthium:

https://github.com/xanthium-enterprises/RTS-DTR-Pin-Control-Linux

However, I only needed to toggle the DTR pin of my USB-serial adaptor, so I removed everything else (like toggling other pins such as DTS, etc...).

Links

• https://github.com/zoobab/ch340g-bitbanging
• https://github.com/xanthium-enterprises/RTS-DTR-Pin-Control-Linux
• http://www.linuxtv.org/mailinglists/vdr/2003/02-2003/msg00543.html
• http://www.action.be/fr/lampe-r-tro-led-sur-tirette-div-couleurs
• https://en.wikipedia.org/wiki/Data_Terminal_Ready
• http://stackoverflow.com/questions/27673344/trouble-in-setting-dtr-rts-pins-of-serial-port-using-ioctl-call-in-linux
• http://linux.die.net/man/1/pport