Hello! My USB Serial Port is not working, what should I do?

First you need to be sure that your equipment meets the requirement listed in the app description or Hardware Page (USB-to-Serial Port). None of the instructions below will help if your phone is out of specifications. The following image shows correct components and hookups for USB-OTG.

Troubleshooting Steps

1. When Serial Port is first plugged in the Android device, the Android operating system gives you option to select the app to associate the USB serial port. When Modbus Monitor Advanced App is selected as an option, the App is started. However, during this startup the app is not able to get the handle to the driver and will not be able to detect the serial port. So, it is best to exit the app and start again (2nd time with USB cable left plugged in) to reliably connect and detect the attached USB serial port.

2. Be sure that the phone is USB – OTG compatible. Not all phone, tablets, or mini-computers have hardware to support the feature even if Android OS may support it.

3. Then you have to have the USB-OTG cable connected. The normal USB won’t work. See the Hardware page for suggestions.

4. If steps above looks good than verify it by checking it with these two (Free) utilities from the Google Play store:

  • Prolific Android App (Prolific – Type USB Serial Port dongles)
  • FTDI Android APP (FTDI – Type USB Serial Port dongles)

5. If any of the utilities don’t detect your USB serial port then you want to check your USB-OTG cable. Did you buy the good quality USB-OTG cable for your type of device? Use following utility from Android Play store to check the USB-OTG cable:

6. If the answer to both of USB-OTG Checker utilities above is “not good” then your phone may not have USB-OTG feature enabled (even though Android 4.3 supports it…each manufacture may not enabled it). If both of those utilities shows “good” results, then be sure that you have given the permission to use USB device to Modbus Monitor Advanced. The permission dialog box pops-up as soon as you plug in your USB port and ask you to choose the app that will have an access to the serial port…you want to choose the “Modbus Monitor Advanced”. To see this in action, you want to check the YouTube Video on the Home Page.

What is Modbus (TCP) Server?

Very simply, it serves data to any client connected in TCP/IP format. The protocol that is used to communicate is the Modbus TCP, only. The same Modbus Monitor Point list that is used during Modbus Master mode can be used in the Server mode. The most common port that Modbus Protocol uses is the Port 502. However, that port is not available to the android developers and locked. If fact any port less then 1024 are not available unless the Android device is rooted. Thus, the user of the Modbus Monitor Advanced must choose the port in the valid Android Range ( > 1024). Your Modbus Master device must also use the same port to talk to Modbus Monitor Advanced Server, to work properly. The well tested port that was during testing is the number “8888”.

What can I do with Modbus (TCP) Server?

Most common application is to check your Modbus Master. That’s correct, you can check all of your setup. The protocol that is used to communicate is the only Modbus TCP, only. Be sure to set that there are not port conflicts. Or refer to Modbus Monitor Slave section of user’s guide for more information about this configuration.

The Modbus Monitor Advanced is two application in one and thus, you can use Master Mode on one phone and Server mode on the other phone/tablet and the app can talk to itself in Master (Client) and Slave (Server) mode. This is a great way to validate your app settings, IP Address conflict, and learn the app.

Second most common (and innovative) use of the Modbus TCP server is to extract Sensor Data from the phone (tablet or minicomputer). For example, let’s say you want to read the phone’s orientation sensor remotely. This is possible simply selecting the correct sensor from the Sensor drop down list. Additional information on this feature can be found on the Modbus Server page. The YouTube video also shows how to use this feature (1:32 time marker).

What is Sensor Server?

The Sensor Server is the extension of the Modbus TCP Server feature (explain above) with added benefit to stuff data from your Android mobile device into the Modbus Registers. In other words, you can turn your phone into portable Modbus TCP Server that is able to relay any (or all) of your sensor data. Example of sensors are: GPS, Light Sensor, Accelerometer, Gyro, Barometer, etc. Most sensor raw data comes directly as three Float values. This feature stuffs this raw values in to (6) Modbus TCP registers. Refer to Sensor Server Page for more information. This feature is included in the Modbus Monitor Advanced App and doesn’t require you to purchase anything extra.