RS485 with SN75176BP doesn´t work

Projects Networking, Protocols, and Devices
1

Hi.

I`m trying to connect several arduinos trought rs485.

If i don´t use the rs485 net:
The ATmega chip is sending a number which increments each 1000 ms therefore if i connect an arduino board with the chip and open the serial monitor I can see the increasing numbers list. I mean, there isn´t any problem with the uploaded schema and chip is working fine.

If I try to send this numbers throught RS485: It doesn´t work

I´ve made two boards with chip SN75176BP but it doesn´t seems to work so now I´m trying with the same circuit on a breadboard.

That´s what i´ve done:

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Arduino_board_1 (with ATmega chip) ---> SN75176 ---> SN75176 ---> Arduino_board_2 (without ATmega chip) ---> PC

SN75176_num1:

pin1 --> no connected
pin2,pin3 -->together to HIGH.
pin4 --> to Arduino_board_1 Tx
pin5 --> +5v
pin6 --> A
pin7 --> B
pin8 --> GND

SN75176_num2:

pin1 --> to Arduino_board_2 Rx
pin2,pin3 --> together to LOW.
pin4 --> no connected
pin5 --> +5v
pin6 --> A
pin7 --> B
pin8 --> GND

Then I plug the Arduino board without Atmega chip to the PC via USB and open serial monitor but it doesn´t receive anything (nor board´s Rx led blinks).

I´ve twisted A-B wire.
I´ve tried with different values for terminal resistors and even without any resistor at all.

¿Any thoughts?
¿Is there any way to check the net without an oscilloscope?

Thanks in advance.

2

Try with this schema, it juste set to ground unused pins of the 485 drivers.

May be it can help you.

Are you sure that your drivers are still ok ?

Don't cross A-B connections ! A must be wired to A, and B to B !

3

Thanks Grag38 but I´ve resolved the problem .

I connected the RO to the Rx of the arduino without chip trying to sniff the data and nothing was happening.
When I plugged the wire to the Tx pin I started to see all the data I was sending.

I was thinking on recibe data when I should had send it through FTDI chip, so connect to Tx pin.

I don´t understand yet why wasn´t Rx led blinking when it was connected to Rx.

Greetings