It’s often handy to communicate to RS485 devices via a USB port, in this project a design for a USB to RS485 converter is shown based on the FT232R chip from FTDI.

The FT232R is configured in the standard way as USB to UART chip and drives U1 the MAX487 RS485 transceiver the direction is controlled by TXDEN.

TX and RX transmissions are indicated by the 2 LED’s D1 and D2.

Termination can be selected by J1, and the RS485 connections are made by a 3 way terminal connection.

The board is designed on a 2 layer PCB as shown below

The bill of materials for this project is all capacitors, Resistors, diodes and inductors are 0805 case style with the exception of C4 which is 1206.

QTY          PART-REFS           VALUE              

---              ---------                      -----              

Resistors

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2                R1,R2                       270                

1                R3                            10k                

2                R4,R5                      120                

Capacitors

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2                C1,C2                       47p                

3                C3,C5,C7                100n               

1                C4                            4u7                

1                C6                            10n                

Integrated Circuits

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1                U1                             MAX487             

1                U2                              FT232R             

Diodes

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2                D1,D2                       DIODE-LED          

Miscellaneous

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1                CN1               USBCONN            

1                J1                  CONN-SIL2          

1                J2                  TBLOCK-I3          

1                L1                  MI0805K400R-00