I am trying to send a command from a bash shell to my Arduino Uno.
I have the following code running on the Arduino:
int LedPin = 13;
int val = 0;
void setup() {
Serial.begin(9600);
pinMode(LedPin, OUTPUT);
}
// Read Value from serial and set a led high or low
void loop () {
val = Serial.read();
if (val == '0') {
digitalWrite(LedPin,LOW);
}
if (val == '1') {
digitalWrite(LedPin,HIGH);
}
}
From bash, I can set the led high or low using screen and then press 0 or 1:
virtualmix@bluedragon:~$ screen /dev/ttyACM0
I would like to set the led high or low using echo:
echo 1 > /dev/ttyACM0
But it doesn't work.
Am I doing it wrong? Is there any known issues using the echo command, or anything I have missed out?
I would guess that screen opens the serial port once, and keeps it open, and that echo opens the port, sends the data, and closes the port.
Opening and closing the serial port causes the Arduino to reset. The echo command sends the data before the Arduino is ready to read it, so it gets lost. The immediate reset causes the action, even if the data was received to not be executed.
There are ways to modify the Arduino to prevent a reset on the opening of the serial port.
Hello since you are using linux why not try gtkterm if you have graphic envirement ofcorse to test it.
If not you should this example to configure the port
stty -F /dev/ttyS0 ispeed 9600 ospeed 9600 -ignpar cs8
-cstopb -echo
In my case 9600 baud, no parity, one stop bit.
Then wrote the data you need to send into a file (using hexedit) and
send the file's contents:
cat commando0.dat > /dev/ttyS0
Also check if you port is ttyS0!!
Hugo007 was right, the problem is due to the serial port being closed after each connexion and the Arduino restarting every time because of its auto reset feature.
Anyway, I have tried a few different solutions and investigate this issue a bit further but it does not seem to have an elegant solution.
So far, the best solution I have found, but not tested, is to plug a 120 Ohm resistor between 5V and reset pin.
I couldn't find any "software solution" that successfully disabled the auto reset feature.
Also, I played a bit with gtkterm and it seemed similar to "screen" in some ways but does not satisfy my need to send command directly from a bash script.
Thanks again for your support and if there is anything new, I am still open to discuss this issue.
Hi all,
I faced exactly the same problem as described above:
When character device opens, Arduino resets.
If I wait for 3 sec after open (wait until Arduino boots), communication works great, however my Arduino counts things and I would like to get back the result - so reset is not acceptable.
stty -F /dev/ttyUSB0 -hupcl works during tests with my laptop (Acer - Ubuntu 19.04) however at the final place with a router (TP-Link - LEDE/OpenWRT) does not.
connecting a 150 Ohm resistor to 3.3V - 5V or put a 10 uF capacitor is not an option because I would like to upgrade my Arduino remote via USB/IP, so I needed a "soft" reset-inhibit.
My solution:
I sacrificed one pin - connected to reset pin, which is
initialized as OUTPUT-HIGH (actually first initialized as INPUT_PULLUP than OUTPUT to be sure we do not get reset during setup).
v_mark:
Hi all,
I faced exactly the same problem as described above:
When character device opens, Arduino resets.
...
that is the very essence of the serial communication and the concept of Arduino using DTR to reset for programming.
For my part I am connecting Arduino mini pros directly from TX-RX to the GPIO uart and don't experience any reset upon calling the serial report or serial plotter.
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I get the same problem too. I use Arduino Uno with Ubuntu 12.04. After a few hours of searching and trying, I find out that Arduino will reset when the serial device is opened for the first time,but will not reset when the serial device is opened again.
So, run command - echo "input string" > /dev/ttyXXX in bash will reset Arduino and send "input string" immediately. Arduino need take some time to initialize, and is not quick enough to receive this string. cat /dev/ttyXXX will reset Arduino too.
When /dev/ttyXXX is opened in somewhere firstly, these commands will work.
Here is my solution:
open /dev/ttyXXX by redirecting /dev/ttyXXX to file description 3