Content Menu
● Introduction to USB to RS232 Adapters
>> Why Use USB to RS232 Adapters?
>> Components Needed
● Step-by-Step Assembly
>> Step 1: Prepare the Components
>> Step 2: Connect the USB to RS232 Chip
>> Step 3: Connect the RS232 DB9 Connector
>> Step 4: Assemble the Circuit
>> Step 5: Test the Circuit
● Software Setup
>> Installing Drivers
>> Configuring the COM Port
● Troubleshooting Common Issues
>> Driver Installation Issues
>> Ground Connection Issues
>> Baud Rate Issues
● Applications and Examples
● DIY Alternatives
● Conclusion
● Frequently Asked Questions
>> 1. What is the purpose of a USB to RS232 adapter?
>> 2. How do I install drivers for my USB to RS232 adapter?
>> 3. What are the common chips used in USB to RS232 adapters?
>> 4. How do I configure the COM port settings for my adapter?
>> 5. What are some common applications for USB to RS232 adapters?
● Citations:
Creating a USB to RS232 cable is a useful project for anyone needing to connect older serial devices to modern computers. This guide will walk you through the process, including the necessary components, assembly, and software setup.
Introduction to USB to RS232 Adapters
USB to RS232 adapters are essential for converting a USB port into a serial RS232 port, allowing communication with devices that only have serial interfaces. These adapters are commonly used in industrial control systems, CNC machines, and other legacy equipment.
Why Use USB to RS232 Adapters?
- Compatibility: Many older devices only support RS232 connections, making these adapters crucial for maintaining compatibility with modern computers.
- Convenience: They allow users to connect serial devices without needing a dedicated serial port on their computer.
Components Needed
To build a USB to RS232 cable, you will need the following components:
- USB to RS232 Chip: Commonly used chips include the FTDI FT232RL or the Prolific PL2303. The FTDI chip is widely supported and reliable.
- RS232 DB9 Connector: This is the standard connector for RS232 devices.
- USB Type-A Connector: This connects to your computer.
- Cable and Wires: For connecting the components.
- Breadboard or PCB: For assembling the circuit.
Step-by-Step Assembly
Step 1: Prepare the Components
Ensure all components are available and ready for assembly. If using a breadboard, prepare it by cleaning any debris.
Step 2: Connect the USB to RS232 Chip
Connect the USB connector to the USB to RS232 chip. Ensure that the D+ and D- wires are correctly connected to the chip's corresponding pins.
Step 3: Connect the RS232 DB9 Connector
Connect the RS232 DB9 connector to the chip. The pinout for a standard RS232 DB9 connector is as follows:
| Pin Number | Signal Name |
| 1 | DCD |
| 2 | RXD |
| 3 | TXD |
| 4 | DTR |
| 5 | GND |
| 6 | DSR |
| 7 | RTS |
| 8 | CTS |
| 9 | RI |
Step 4: Assemble the Circuit
Place the components on the breadboard or PCB and connect them according to the circuit diagram. Use jumper wires to connect the USB and RS232 connectors to the chip.
Step 5: Test the Circuit
Before final assembly, test the circuit to ensure it works correctly. Use a multimeter to check for any shorts or incorrect connections.
Software Setup
Installing Drivers
To use your USB to RS232 adapter, you need to install drivers on your computer. The most common drivers are for FTDI chips.
1. Download the Driver: Visit the FTDI website and download the appropriate driver for your operating system.
2. Install the Driver: Follow the installation instructions provided with the driver.
Configuring the COM Port
After installing the driver, you may need to configure the COM port settings:
1. Open Device Manager.
2. Find the newly installed serial port under Ports (COM & LPT).
3. Right-click on it and select Properties.
4. In the Advanced tab, you can change the COM port number if needed.
Troubleshooting Common Issues
Driver Installation Issues
One of the most common problems with USB to RS232 adapters is getting the proper driver installed. The driver must correspond to the chip inside the cable, not the manufacturer of the cable. FTDI and Prolific are the primary chip manufacturers, with FTDI being widely supported and reliable[1].
Ground Connection Issues
Ensure that the ground connection on the USB side of the adapter is properly connected to pin 5 of the DB-9 connector. This is crucial for maintaining a stable signal ground. If both adapters are connected to the same PC host, the ground issue is lessened because both USB ends share the same ground[3].
Baud Rate Issues
Older cables may struggle with higher baud rates, such as 115200 baud, but still work at lower rates. This can be due to the quality of the cable or the chip used[1].
Applications and Examples
USB to RS232 adapters are used in various applications:
- Industrial Control Systems: For controlling machinery and monitoring processes.
- CNC Machines: For sending commands and receiving data from CNC devices.
- Legacy Equipment: For maintaining compatibility with older systems.
DIY Alternatives
For those interested in DIY projects, creating a USB to TTL converter can be a cost-effective alternative. This involves using chips like the CH340G, which is a low-cost alternative to other USB to TTL converter ICs. It supports Windows and macOS and is easy to install[8].
Conclusion
Creating a USB to RS232 cable is a straightforward project that requires basic electronics knowledge and the right components. By following this guide, you can ensure compatibility between modern computers and older serial devices. Remember to troubleshoot common issues like driver installation and ground connections to ensure reliable operation.
Frequently Asked Questions
1. What is the purpose of a USB to RS232 adapter?
A USB to RS232 adapter converts a USB port into a serial RS232 port, allowing communication with devices that only support serial connections.
2. How do I install drivers for my USB to RS232 adapter?
Download the appropriate driver from the manufacturer's website and follow the installation instructions. Common drivers include those for FTDI chips.
3. What are the common chips used in USB to RS232 adapters?
Commonly used chips include the FTDI FT232RL and the Prolific PL2303. The FTDI chip is widely supported and reliable.
4. How do I configure the COM port settings for my adapter?
Open Device Manager, find the serial port under Ports (COM & LPT), right-click on it, select Properties, and adjust settings as needed in the Advanced tab.
5. What are some common applications for USB to RS232 adapters?
They are used in industrial control systems, CNC machines, and for maintaining compatibility with legacy equipment.
Citations:
[1] https://www.campbellsci.de/blog/usb-rs-232-adapter-cable-issues
[2] https://hub.digi.com/dp/path=/support/asset/technical-note-tn258-usb-to-rs-232-converter-cable-users-guide/
[3] https://superuser.com/questions/1688901/why-some-usb-serial-converters-work-and-others-dont-on-specific-hardware
[4] https://www.gemu-group.com/gemu-cdn2/dokumente/1/ba_USB_TO_RS232_23.09.09_gb.pdf
[5] https://www.coolgear.com/wp-content/uploads/2015/12/USB-232TTLMOS-IS-Installation-Guide-2.pdf
[6] https://aveosystems.com/troubleshooting-rs-232-connections/
[7] https://jethomson.wordpress.com/2010/02/21/diy-usb-to-serial-cable-for-3usd/
[8] https://www.instructables.com/DIY-USB-to-TTL-Converter/
[9] https://asset.conrad.com/media10/add/160267/c1/-/en/000972543ML01/manual-972543-usb-20-adapter.pdf
[10] https://www.youtube.com/watch?v=0lagBHIMHX4
[11] https://powersight.com/FILES/APPLICATION_NOTES/USB-RS232%20Installation.pdf
[12] https://www.adamdu.com/docs/rs232_to_usb_problem_solving.pdf
[13] https://www.infineon.com/dgdl/Infineon-AN85514_Designing_a_USB_to_RS232_Solution_Using_Infineon_USB_UART_LP_Bridge_Controller-ApplicationNotes-v05_00-EN.pdf?fileId=8ac78c8c7cdc391c017d073b82f25f8f
[14] https://sgcdn.startech.com/005329/media/sets/icusb232proc_manual/icusb232proc_qsg.pdf
[15] https://www.gearmo.com/usb-serial-troubleshooting-a-usb-to-serial-adapter/
[16] https://customer.cradlepoint.com/s/article/USB-to-RS232-Extensibility-Cable-Quick-Start-Guide
[17] https://sgcdn.startech.com/005329/media/sets/icusb232v2_manual/icusb232v2_qsg.pdf
[18] http://odysseydatarecording.com/download/USB_To_Serial_Cable_Troubleshooting.pdf
[19] https://www.youtube.com/watch?v=PosPLX8Qw08
[20] https://www.waveshare.com/wiki/USB-TO-RS232-Male-Cable
