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could you propose me a schematic to interface USB with RS232?
thierrybabonneau

thierrybabonneau

@copilot could you propose me a schematic to interface USB with RS232?
2y

copilot

Certainly! When interfacing USB with RS232, you'll typically use a USB-to-Serial converter IC. A popular choice for this application is the FT232R from FTDI or the CP2102 from Silicon Labs. Both of these ICs convert signals from USB to the serial UART signals necessary for RS232 communication, but they output TTL-level signals. To fully comply with RS232 standards, which require signal levels to be in the range of ±3V to ±15V, you'll need an additional chip to convert TTL signals to RS232 voltages. The MAX232 IC from Maxim Integrated is frequently used for this purpose.
Here's a basic schematic proposal using the FT232R for the USB-to-Serial conversion and the MAX232 for the TTL to RS232 level shifting:
Components Needed:
  1. FT232R IC (USB to serial UART converter)
  2. MAX232 IC (TTL to RS232 converter)
  3. USB Connector: Type B or micro, depending on your preference.
  4. DB9 Connector (RS232 standard connector)
  5. Capacitors:
    • Four 1μF capacitors for MAX232.
    • A 100nF decoupling capacitor for FT232R.
  6. Resistors:
    • (10K\Omega) pull-up resistor for the FT232R RESET pin.
  7. Crystal Oscillator: 12MHz for the FT232R (optional, since FT232R can also use an internal oscillator).
Schematic Connections: USB Side (FT232R):
  • Connect USB Connector D+ to FT232R:USB_D+.
  • Connect USB Connector D- to FT232R:USB_D-.
  • Connect FT232R:GND to the common ground.
  • If using an external crystal oscillator:
    • Connect Crystal Oscillator to FT232R:XTAL1 and FT232R:XTAL2.
  • Connect a (10K\Omega) pull-up resistor from FT232R:RESET# to VCC (to ensure the device does not reset).
  • Connect VCC to FT232R:VCC and a (100nF) decoupling capacitor between FT232R:VCC and GND.
RS232 Side (MAX232):
  • Connect FT232R:TxD to MAX232:T1IN (TTL Input).
  • Connect FT232R:RxD to MAX232:R1OUT (TTL Output).
  • Attach four (1\mu F) capacitors as per the MAX232 datasheet:
    • One between MAX232:VCC and MAX232:GND.
    • One between MAX232:C1+ and MAX232:C1-.
    • One between MAX232:C2+ and MAX232:C2-.
    • One between MAX232:C3+ (or V+) and MAX232:C4- (or V-).
  • Connect MAX232:R1IN to DB9 Pin 2 (RS232 RX).
  • Connect MAX232:T1OUT to DB9 Pin 3 (RS232 TX).
  • Connect MAX232:GND to the common ground.
This is a basic interface schematic. Depending on your application, you might also need to connect control signals like CTS, RTS, DSR, DTR, etc. Or you may not need these if your communication is straightforward without hardware flow control.
Please, adapt capacitor values if necessary, as $1\mu F$ for MAX232 capacitors is a common but not universal choice; specific requirements depend on the version of the MAX232 or the operating voltage.
This should give you a good starting point for interfacing USB with RS232 in your project. Let me know if you need further details or modifications!
2y
2
could you connect me the different components to realise a RS232 to USB converte...
thierrybabonneau

thierrybabonneau

@copilot could you connect me the different components to realise a RS232 to USB converter ?
2y

copilot

To realize an RS232 to USB converter with the given components, you'll need to follow these steps for the connections. The FT232RL chip (IC1) will be the USB to Serial UART interface, and the MAX232D chip (U1) will handle the RS232 voltage level conversion. Here are the suggested connections based on the components you've provided:
Power Connections
  • Connect IC1:VCC (pin 20) to J2:8 (VBUS) for USB power.
  • Connect IC1:GND (pins 7, 18, 21) to J1:4 (GND) for ground connection.
  • Connect U1:VCC (pin 16) to J2:8 (VBUS) for USB power.
  • Connect U1:GND (pin 15) to J1:4 (GND) for ground connection.
USB to Serial Connection (FT232RL)
  • Connect J1:D- (pin 6) to IC1:USBD- (pin 16).
  • Connect J1:D+ (pin 7) to IC1:USBD+ (pin 15).
Serial to RS232 Connection (MAX232D)
  • Connect U1:T1OUT (pin 14) to J2:3 (RS232 TX).
  • Connect U1:R1IN (pin 13) to J2:2 (RS232 RX).
  • Connect IC1:RXD (pin 5) to U1:T1IN (pin 11).
  • Connect IC1:TXD (pin 1) to U1:R1OUT (pin 12).
Crystal Oscillator for FT232RL
  • Connect Y1:P1 (pin 1) to IC1:OSCI (pin 27).
  • Connect Y1:P2 (pin 2) to IC1:OSCO (pin 28).
Capacitors for MAX232D (Assume typical values of 1μF for charge pump capacitors)
  • Connect capacitors between U1:C1+ (pin 1) and U1:C1- (pin 3), and between U1:C2+ (pin 4) and U1:C2- (pin 5). Another pair of capacitors should be connected between U1:VS+ (pin 2) and U1:VCC (pin 16), and between U1:VS- (pin 6) and U1:GND (pin 15), according to the MAX232D datasheet for creating the necessary voltage levels for RS232 communication.
This setup configures the FT232RL for USB to Serial conversion and the MAX232D for RS232 signal level conversion. The connections above are geared towards a basic converter; further fine-tuning might be needed depending on specific requirements, such as flow control pins if required.
2y
3
IC1
End of Life
J2
U1
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Big Peach Universal Remote

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