In this post, I will explain how to open serial port to your Arduino or SDI-12 USB adapter by its unique ID so you always open the correct port even when there are multiple such devices on your computer or raspberry pi.
For Arduino and SDI-12 USB adapter users, I have a nice trick to help you manage multiple Arduinos or SDI-12 USB adapters on the same computer or raspberry pi. On raspberry pi, as on a typical linux system, your device shows up as a serial port, such as /dev/ttyUSB0. This serial port designation is usually bound by the order that the device is discovered at boot time, which may not be the same even if you keep your adapter plugged into the same USB port. This means if you have more than one device on your raspberry pi, you may open the wrong port at times, which should be a big issue. To prevent your program from opening the wrong port, you need a unique ID for each device. Luckily FTDI chips already come with unique IDs. We just have to find those IDs and possibly change them into more meaningful things for us to remember. Assume for the moment you are making a data logger for your test fields. There is one field that can be called “NORTH”. The following steps will help you change the ID of the FTDI chip on your device so you can later open its port by that ID, instead of a port name. Here is a list of which devices are using FTDI’s chips that have the reprogrammable ID feature:
- Liudr SDI-12 USB adapter (all types)
- Sparkfun Redboard
- Certain Arduino clone boards
- Lots of other devices such as GPS etc.
Here is the FT_PROG tool FTDI provides. It’s windows only but I’m sure you can find a windows machine to run it. I’ve not tested it in a virtual machine whose host is linux or macos. I’ll do that when I have more time. If you are unsure whether your device has an FTDI chip, a quick scan using the program will tell you.
http://www.ftdichip.com/Support/Utilities.htm#FT_PROG
First, press the scan icon (magnifying glass). If you have a device with FTDI chip, it will show up. See the screen grab below:
So I have an FT232R chip with a chip serial number “A106DHE5”. I can open port with this serial number but I’d rather change it to “NORTH”. Click on the “SerialNumber” from the left side.
Uncheck the “auto generate serial no” so you can edit the serial number to “NORTH”. You have up to 16 characters to name the adapter. Once done, press flash icon (thunder bolt).
Now that you have programmed your chip, you can read the information back using “scan” again to verify that the ID has changed:
Now that you have this nice ID, let’s open port by this ID.
Here is a small complication. On linux, the chip ID is returned, such as “NORTH”. On window, the port ID is returned, such as “NORTHA“. The addition of the “A” indicates the port “A” on chip “NORTH”. This is because some FTDI chips have two serial ports. The port IDs will be “NORTHA” and “NORTHB“. Even for FTDI chips that have only one port, such as for our case, the “A” is still there. So I recommend comparing chip ID instead of port ID. If you only work on linux/rpi systems, this doesn’t seem to concern you. But if you wish to make your code platform independent, i.e. running on windows without an incident, you will only extract whichever ID you receive with the stored chip ID, up to the length of the stored chip ID. Note: in the platform-independent code, you can’t slice a port’s serial_number with your stored ID because some internal ports don’t have serial numbers thus returns empty that will throw an error when you try to slice an empty array.
The following is a snippet that works ONLY on linux/rpi systems:
[sourcecode language=”python” wraplines=”false” collapse=”false”]
import serial.tools.list_ports # For listing available serial ports
import serial # For serial communication
my_ID=’A817EQLG’
port_device=”
# List ports for user to select
a = serial.tools.list_ports.comports()
print(‘\nDetected the following serial ports:’)
for w in a:
print(‘Port:%s\tID#:=%s’ % (w.device, w.serial_number))
if (w.serial_number==my_ID): # Match ID with the correct port
port_device=w.device # Store the device name to later open port with.
if len(port_device)!=0:
print(‘\r\n%s is the correct port.’ %(port_device))
else:
print("Port with ID: %s is not found!" %(my_ID))
[/sourcecode]
The following is a snippet that works on ALL OS:
[sourcecode language=”python” wraplines=”false” collapse=”false”]
import serial.tools.list_ports # For listing available serial ports
import serial # For serial communication
my_ID=’A817EQLG’
port_device=”
# List ports for user to select
a = serial.tools.list_ports.comports()
print(‘\nDetected the following serial ports:’)
for w in a:
print(‘Port:%s\tID#:=%s’ % (w.device, w.serial_number))
if (w.serial_number.__str__()[:len(my_ID)]==my_ID): # Match ID with the correct port
port_device=w.device # Store the device name to later open port with.
if len(port_device)!=0:
print(‘\r\n%s is the correct port.’ %(port_device))
else:
print("Port with ID: %s is not found!" %(my_ID))
[/sourcecode]
Your choice, simplicity of code or cross-platform compatibility.
Here is the cross-platform code’s result on my windows machine:
Detected the following serial ports:
Port:COM23 ID#:=A817EQLGA
Port:COM3 ID#:=None
COM23 is the correct port.
As you can see, there is an added “A” at the end of the ID reported by windows, which the python code ignored to produce a match.
I’ve also attempted to do this using Processing 3.0. Unfortunately, the Serial.getProperties() function that should return similar information returns blank (possibly not implemented on windows and yet to be tested on linux). If you have tested Processing method with success, please reply below with your results. I’ll add your comment to the post.
Here is the code I used in Processing 3.0:
[sourcecode language=”java” wraplines=”false” collapse=”false”]
import processing.serial.*;
import java.util.Map;
void setup() {
String[] ports = Serial.list();
for (int i=0; i < ports.length; i++) {
Map<String, String> props = Serial.getProperties(ports[i]);
print(ports[i]+": ");
println(props);
}
}
[/sourcecode]
Results:
COM3: {}
COM23: {}
:(
Closing note: even if you work on Windows that assigns unique COM port number to your arduino or adapters, the assignment relies entirely on the currently available port numbers. If you develop your project on one windows PC and deploy on another windows PC, you WILL get different COM port numbers. On a Mac, the ID is embedded on the port name such as /dev/ttl.usbserial-A103RU9T so you are better off. But, will you be willing to shell out the money to get a mac and have it sit somewhere to collect data just because of this feature? If you are a linux wiz, you can bind names with serial numbers using some scripts. That’s beyond the scope of our general discussion, which assumes minimal experience with linux administration.
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