This is a low cost non-isolated bi-directional RS485 to RS232 converter which can be plugged into PC's serial port (DB-9) directly. Hence it extends the communication range over 1KM with speed of 115K bit/s easily. The power consumption is small and a 9V/100mA (2.1mm center positive) plug pack will do fine.
OPERATION
Since KC485 supports only half-duplex communication, the direction of communication is controlled by the RTS (Request-to-send) signal of the PC. If the RTS is inactive, the KC485 is in receive mode. While the RTS is active, the KS485 is in transmit mode. For normal operation, always put the KC485 in receive mode unless transmission is needed. (Make sure the last bit has been transmitted before switching back to receive mode) 32 units of KC485 can be connected in parallel to form a small communication network. (Remark: the terminating resistor R6 and the biasing resistors R7, R8 should be removed from the circuit, they can only presented on both ending units)
CIRCUIT DESCRIPTION
The circuit is pretty straight forward. U1 converts the RS232 signals from PC to logic level. Then the logic level is converted to RS485 signals by U2. U3 provides stable 5V power supply. Three LEDs are added for diagnostic. D3 lites up in receive mode and goes off in transmit mode. D2 flashes when transmitting. D1 flashes when receiving.
Canadian Dollars
