Cheap USB to UART Converter using Microchip MCP2200

Nowadays, USB ports are widely used for data transactions between electronic devices and computers. In many scenarios, there is no need to communicate with the USB port directly, so electronic designers use USB to UART (RS232-Serial) adapter chips, so the USB port is converted into a virtual COM port on the computer. The initial idea of ​​many designers is to use FTDI chips to convert USB to UART. There is nothing wrong with FTDI chips, however, but they are more expensive. In this article / video, I will introduce a cheap USB to UART converter that uses the Microchip MCP2200 chip. The switch supports both 3.3V and 5V serial logic levels and uses three LEDs to deliver power, transmit data, and receive data. The unit supports CTS and RTS serial pins, as well as six GPIOs that can be used for direct control of connected devices. Module serial data was examined and decoded using the UART decoding feature in the Siglent SDS2102X Plus oscilloscope. So let’s get started! Circuit analysis Figure 1 shows the schematic diagram of the USB to UART converter. The diagram has been broken down into a few parts for a better visual inspection. Figure 1 The schematic diagram of the USB to UART IC1 converter is the MCP2200 [1] USB to Microchip UART adapter chip. It supports Hi-Speed ​​USB up to 12MB / s and is available in a 20-lead SOIC package. So this component is easy to solder to prototypes. It is also equipped with RTS and CTS pins, and six GPIOs. R1 is a pull resistor for the reset pin and C1 and C2 are disconnecting capacitors to reduce the supply noise. C3, C5 and Y1 are building a clock generating unit. C6 reduces VUSB rail noise. USB1 is an SMD USB-mini connector for connecting a USB cable. C4 and FB1 reduce + 5V USB supply noise. Figure 2 shows a picture of a SMD USB-B mini connector. Figure 2: The SMD USB-mini REG1 connector is RT9166-33GX [2], Which is a 3.3V linear regulator in a small SOT-89 package. According to the datasheet: “The RT9166 / A series are low-leakage CMOS regulators optimized for ultra-fast transient response. The devices are capable of supplying 300mA or 600mA of output current with a leakage voltage of 230mV or 580mV respectively. The RT9166 / A series is optimized for CD / DVD- applications. ROM or CD / RW or wireless communication supply. RT9166 / A regulators are stable with output capacitors as low as 1 ° F. Other features include ultra-low leakage voltage, high output precision, current limiting protection, and high ripple rejection ratio. Devices are available in Constant output voltage range of 1.2V to 4.5V with 0.1V per step.The RT9166 / A regulators are available in SOT-23 three-head (RT9166 only), SOT-89, SOT-223, TO-92 and TO-252 “packages. The P3 is a 3-pin male header that allows the user to switch between 3.3V and 5V logic levels, only using a jumper. D1, D2 and D3 are three SMD LEDs indicating correct USB cable connection, data transmission and reception. R2, R3 and R4 are used to limit the LED current. Figure 3 shows the PCB layout of the USB to UART adapter unit PCB layout. It is a two-layer PCB and all component packages are SMD (excluding pin headers). Figure 3: The PCB layout of the USB to UART adapter using the MCP2200 Figure 4 is a separate display for the top and bottom two layers, so the red layer is the top and the blue layer is the bottom. Figure 4: Separate view of the top and bottom layers of the PCB When I decided to design the schematic and the PCB for this project, I realized I don’t have libraries configured for IC1[3] And REG1[4] In my component libraries store. So I decided as usual to go with the categorized SamacSys IPC component libraries and installed the missing libraries (schematic code, PCB footprint, 3D model) using the free SamacSys tools and services. There are two options for importing libraries into a CAD electronic design program: you can visit componentearchengine.com and download and import libraries, or you can use SamacSys CAD plugins and search / import models directly into the design environment. Figure 5 shows all supported electronic design CAD software [5]Obviously, all known software are supported. I am using Altium Designer, so I searched for and installed missing libraries with the SamacSys Altium plugin (Fig 6) [6]. Figure 5: All electronic design CAD software supported by SamacSys Plugins Figure 6: Component Libraries Defined in the SamacSys Altium Plug-in Assembly Figure 7 shows a top view and Figure 8 shows a bottom view of the assembled PCB board. PCB boards were manufactured by PCBWay. Got up to 10 paintings with no change in price. The copper mask, silk screen and solder quality were good, so I had no problem soldering the components at all. The smallest component package size is 0805. Fig. 7: Top view of the assembled PCB board Fig. 8: Bottom view of the assembled PCB board Test and Measurement After welding is finished (or receiving the assembled board), you must connect to the computer module and configure the MCP2200 chip, if needed Command. Microchip has provided a chip configuration utility program [7], Named “MCP2200 Configuration Tool”. Figure 9 shows a screenshot of the utility program. In my case, on the first try the LEDs were not flickering so I had to enable flashing in the configuration. Figure 9: The MCP2200 Microchip Configuration Tool Figure 10 provides the wiring diagram of the unit. With this guide, you will not have problems with connections and connections. Figure 10 Wiring Diagram for a USB to UART Module I have connected the RX signal of the module (the computer is the transmitter) to a Siglent SDS2102X Plus Oscilloscope [8] To check the signal and decode the data. At the same time, I played with the jumper to switch between 3.3v and 5v logic levels. Figure 11 shows the UART signal and the decoded data and Figure 12 shows the same signal with the list of possible results that can be used to check timing, errors, etc. For more details, please check the video. Figure 11: RX-UART Data Decoded with Siglent SDS2102X Plus Oscilloscope Figure 12: RX-UART Data Decoded with Siglent SDS2102X Plus Oscilloscope (List of Possible Results) Bill of Materials Figure 13 shows the Bill of Materials for this project. Figure 13: Bill of Materials Reference article: https://www.pcbway.com/blog/technology/Cheap_USB_to_UART_Converter_using_Microchip_MCP2200.html
[1]Datasheet: MCP2200: https://www.mouser.se/datasheet/2/268/22228A-81933.pdf
[2]RT9166-33GX Data: https://www.richtek.com/assets/product_file/RT9166=RT9166A/DS9166A-23.pdf
[3]: MCP2200 schematic code, PCB trace, and 3D model: https://componentsearchengine.com/part-view/MCP2200-I%2FSO/Microchip
[4]: RT9166-33GX schematic code, PCB trace, and 3D model: https://componentsearchengine.com/part-view/RT9166-33GX/RICHTEK
[5]: CAD electronic design software plug-ins: https://www.samacsys.com/library-loader-help
[6]: Altium Designer plug-in: https://www.samacsys.com/altium-designer-library-instructions
[7]: Microchip MCP2200 Configuration Tool: https://ww1.microchip.com/downloads/en/DeviceDoc/MCP2200%20Configuration%20Utility%20v1.3.1.zip
[8]: Siglent SDS2102X Plus Oscilloscope: https://www.siglenteu.com/digital-oscilloscopes/sds2000xp.