Python and pySerial make it easy to read weight data from a scale
On the Pi, I used Python with pySerial to read the weight from the scale. The script I put together is trivially simple. You can download it here or just type it on the Pi:
By pressing the PRINT-Button on the scale, I then sent a few weight values to the Pi and the script wrote them to the terminal (b’ is added by Python):
In a more useful application, you would want to parse the data sent from the scale to get the weight as a number and then do something with it (maybe write it to a database). You could also do interesting things with the GPIO on the Pi like sounding an alarm when a certain weight is exceeded (though a microcontroller might be better suited for this).
I then switched the scale to “stream mode” (continuous transmission) where it sent 10 values per second (stable or not). The output you see below is the result of placing a single object on the scale and waiting for it to stabilize:
I hope this example shows that it can be really easy to transfer the weight from a scale to a Raspberry Pi.
Notes on scales and the Raspberry Pi
One advantage of A&D scales is that (almost) all of them use the same data format and interface parameters and that you’ll find a good description in the manual:
However, you could use also use scales made by other manufacturers as long as they come with an RS-232 interface and the ability to send the weight in ASCII format. Available data output modes vary, so please read the product description carefully before buying.
A converter like the one I used is already built into some scales, which means that you can directly connect them to the Raspberry Pi via USB (you won’t need a serial cable). You’ll find many Ohaus scales with this interface option and the ones I’ve tested worked fine. However, cheaper scales with a USB interface can often not be used with pySerial as they do not emulate a serial port. They can also present other challenges (e.g. data that is not transmitted in human-readable ASCII format).
Many scales and balances are equipped with an RS-232 interface. Moxa’s NPort series and similar serial device servers allow you to connect such scales to a network (Ethernet). In this article, I’ll show you how to connect a Moxa NPort 5110A to an Ohaus scale and how to configure and test it.
1. Physical connection
The Moxa Nport 5110A has an RS-232 port (DE9M) on one side and an Ethernet port on the other side:
To communicate with your scale, you’ll need a matching RS-232 cable. The Ohaus Defender 3000 scale used in this example requires a DE9M to DE9F straight (1:1) cable:
Once the physical connection to the scale has been established, the Moxa NPort has to be configured. There are several ways to do so. I prefer the following method:
Connect the NPort directly to a single computer (not a LAN) with an Ethernet cable.
Start the NPort Administrator and locate your NPort by clicking on the Search button:
It should be found at the default IP address (192.168.127.254).
Note: It’s not always necessary to change your PC’s IP address if you’re running the NPort Administrator software. However, if you receive error messages during the following steps, try to temporarily set your computer’s IP address to an address on the same subnet (such as 192.168.127.1).
Select the Ethernet connection under Control Panel > Network and Internet > Network connections, right-click on it and choose Properties, then select Internet Protocol Version 4 (TCP/IPv4) and click on Properties. Make a note of your current settings so that you can restore them later, then enter the temporary IP address:
If the NPort is shown as locked, right-click on it and select Unlock: The default password is “moxa”.
Right-click again and select Configure, then select the Network tab: Enter a static IP address, subnet mask and gateway that work on your network (or select DHCP or BOOTP for automatic address assignment, though this is not recommended for most operating modes).
To make the NPort accessible on our network, I set its IP address to 192.168.0.253:
With the network configuration complete, you can disconnect the NPort 5110A from your computer and connect it to your network (LAN).
3. RS-232 configuration
It is essential that both the NPort and the scale use the same settings for the serial port (RS-232). In the Serial tab, select the port (the NPort 5110A only has one, but you still have to select it), check Modify and click on Settings:
Enter the RS-232 settings found in your scale’s menu or user manual. The default settings of our Ohaus Defender 3000 scale are shown in the screenshot below:
Important: By default, the NPort is set to CTS/RTS flow control! You cannot change this setting when using the Setup Wizard through the web console. As mentioned before, I recommend using the NPort Administrator software instead.
4. Set an operating mode
To change the mode, go to the Operating Mode tab, check Modify, select the port and click on Settings:
The NPort 5110A supports several operating modes, I will only discuss the following two here:
Real COM mode: This mode allows you to create a virtual COM port on a PC and use the scale as if it were connected directly to that PC. This is very useful when you’re using software which only supports connections to COM ports and cannot communicate over TCP/IP (such as our 232key virtual keyboard wedge software).
Please note that you’ll have to install a virtual COM port driver on the PC that communicates with the scale. In my tests on Windows 10, setting up the COM port through NPort Administrator did not create a new virtual COM port on the system. However, using the NPort Windows Driver Manager worked.
TCP Server: The NPort acts as a server, waiting for incoming connections from TCP clients on port 4001 (or on another user-defined port). The maximum number of concurrent connections can be changed from 1 (default) to up to 8. This mode works with software like our Simple Data Logger and many others.
Note: It is not necessary to set the data packing options unless you want to optimize either for minimal latency or maximum throughput. By default, the device will try to find a reasonable compromise (this is likely achieved by observing the delay between the data received over RS-232 to determine when a “line” of data is complete).
When I set the scale to continuous transmission mode (wich has no delay between the weight values), the NPort packed 104 bytes in each Ethernet frame, corresponding to almost 6 weight values (the scale sends 80 values/s):
Depending on the operating mode chosen above, you’ll have to use different programs to test the NPort 5110A. In addition to the software I’ve already mentioned above, you could use the following:
Real COM mode
A terminal program like Termite or HTerm can connect to the virtual COM port. Make sure that the connection parameters correspond to the settings of your scale.
You can use PuTTY set to “Raw” TCP mode to act as a TCP client: The following screenshot shows commands sent to the scale and the replies:Another option is our free TCPTester software. It repeatedly sends a user-defined command to the scale (e.g. to request the weight). Once a reply has been received, the command is repeated:
During testing, it can be useful to observe the LEDs on the NPort:
The “Ready” LED should be green.
The “Link” LED is green when the NPort has established a 100 Mbs Ethernet connection and orange on a 10 Mbps connection.
The Tx/Rx LED flashes orange when the NPort receives data from the scale and flashes green when the NPort is sends data to the scale over the serial port. Therefore, If you’re sending commands to a scale, you should be able to see it flash green. A reply from the scale would cause the LED to flash orange. If this is too difficult to see, consider using the web console to diagnose connection issues (I found it worked best in Firefox):
I hope this article has been useful. What are your experiences with Moxa’s NPort serial device servers? Please don’t hesitate to leave a comment! For support, please contact Moxa or your vendor.
Connecting your scale to a PC and recording the weight should not be a difficult task. However, data logging software available from scale manufacturers or third parties is often expensive, difficult to use or frustratingly unreliable. We developed Simple Data Logger (SDL) to address these issues.
SDL writes the weight received from a scale or balance to a file, optionally adding the date and time. The CSV files generated by SDL can easily be opened in Excel and other spreadsheet applications for further processing and visualization.
SDL currently supports the following connections:
COM port: RS-232, USB virtual COM port, Bluetooth SPP, etc.
TCP/IP: Ethernet, WLAN (raw TCP format only).
Note: Your scale has to send data in ASCII format.
Get started recording weight values with Simple Data Logger
Connect your scale to your computer, download and install SDL, then follow these steps to configure the software ():
Input tab: If your scale or balance is listed in SDL, simply select it and press the set default parameters for device button. Otherwise, select “generic measuring instrument” and enter the interface parameters manually. Set the radio button to match your connection: COM port (RS232, USB VCP, Bluetooth SPP) or TCP/IP.Make sure that you’ve specified a terminator (a.k.a. delimiter, the last character your scale sends in each line of data) or a timeout (e.g. 100ms, SDL will process received data if no additional data is received during this time).
Output tab: Choose a file for the recorded data. SDL will create if for you if it does not exist (otherwise, data will be appended). Choose (or enter) a date and time format or select “None” from the list if you do not want SDL to add the date or time. Pick a decimal separator (for numeric values) and value separator (used to separate values from each other). The correct settings for your locale can be made automatically by clicking on the set values button.
Start tab: Press the start button to start recording data. Press the “PRINT” button on your scale or balance to send the weight to SDL. Depending on you scale, this button might have a different name (e.g. “DATA”). Some scales like the A&D FX-300i used in this example also have to ability to automatically transfer each (stable) weight. Data received will be shown in the event log (with the captured weight value shown in blue) and the weight will be written to the chosen file. Press stop to stop data logging and to close the file.
Note: SDL can also handle continuous streams of weight data if this is what your application calls for (we’ve tested it with a scale which sends 100 values per second). The total number of recorded values is only limited by your disk space (but please keep in mind that Excel cannot open files containing more than 1,048,576 rows).
Process the weight values in Excel (or other spreadsheet applications)
Provided that you’ve made the right format settings in the output tab, you can easily open the CSV file in Excel (or other spreadsheet applications like Google Docs, OpenOffice/LibreOffice Calc). The weight will be recognized as a number, allowing you to make further calculations (i.e. calculating the total weight as shown below): Everything shown here can be done with the “Basic” version of SDL (which is free for personal, non-commercial use). The “Plus” version has additional features including a timer to request the weight from the scale in user-defined intervals.