I'm trying to make an RS232/RS485 converter circuit. I used a circuit from http://airborn.com.au/layout/232cnv/232to485.html site and i changed some components on that circuit. Then I established my converter circuit:
I used copper pour as ground and i connected lacking ground connections with additional wires after the board was prepared. To test my circuit, I used another RS232/RS485 converter circuit which I know that is working without a problem. I connected A and B outputs of my circuit's RS485 connector to the A and B outputs of other circuit's connector. Then i connected these two converter circuits to computer with RS232 USB cable. I tested the communication between these circuits using CuteCOM serial communication terminal. I used two terminals for my circuit and other. (Baud Rate:9600)
I observed that data is transmitting from my converter circuit to other but not receiving from other circuit to mine.
I also tested the other converter circuit with another RS232/RS485 converter circuit which I know that is working without a problem, and i realised that there is not any problem during transmitting and recieving process, so data can be sended and recieved.
These are the list of the changes that i made on original scheme in for my converter scheme;
- Maxim's MAX232CWE was used instead of ICL232.
- Texas Instruments' SN65HVD3082E was used instead of 75176.
- As voltage regulator, Exar's SPX3819 was used instead of LM2936Z5.
- As transistor, BC256A (pnp) was used instead of BC557 (pnp).
- 22 uF capacitors were used instead of 2.2 uF, for the ones connected to MAX232CWE.
- On original scheme, a 6 pin connector was used as RS485 connector and two pins were used for A,B connections, one pin was connected for ground, one pin was connected to the 9th pin (RI - Ring Indicator) of the RS232 connector with a jumper. Unlike these, in my circuit, 2 pin connector was used as RS485 connector and only A,B connecitons were made. (RI and ground connections were not used.)
- On original circuit, A and B pins of SN65HVD3082E RS485 Transreciever were terminated with a 120 Ohm resistor and a jumper. I did not do this on my circuit.
I'm investigating about the problem which can be related with changes that i made on original circuit or another reason. I will be very happy if you share your idea about the problem of just transmitting and not recieving data on my converter circuit.