For another project I’m currently working on, I need a way to control multiple microcontrollers in a multi-point, multi-drop network configuration. Luckily, we live in amazing times. As I write this, you you can buy a fully assembled breakout board for the MAX485 chip from Maxim Integrated for a mere $0.45 USD shipped from China.
I bought a 5 pack, here are some of the boards:
RS485 is an old protocol, but is the logical next step for devices I’m already communicating with via RS232. For this example, I’m using 4 Arduino boards of various types.
- An Arduino Micro as the master
- 2 Slave Arduino Leonardos
- 1 Slave Arduino Pro Mini (5v)
Here is a video of the setup:
The schematic is really straightforward as well. The only tricky bit is that I’m using a software serial port on each of the Arduinos for ease of debugging. Here’s a schematic:
The code to acomplish this is really intuitive as well.
Here is the code for the master Arduino:
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#include <SoftwareSerial.h> int MAX485_Receiver_Output_PIN = 10; int MAX485_Driver_Input_PIN = 11; int MAX485_Driver_Output_Enable_PIN = 12; int debug_led = 13; SoftwareSerial software_serial (MAX485_Receiver_Output_PIN, MAX485_Driver_Input_PIN); // RX, TX void setup() { Serial.begin(9600); // begin hardware serial software_serial.begin(9600); // begin software serial pinMode(MAX485_Driver_Output_Enable_PIN, OUTPUT); digitalWrite(MAX485_Driver_Output_Enable_PIN, HIGH); // this disables Receiver Output Enable and enables Driver Output Enable } void loop() { byte to_send = 0; // declare the byte to be sent to the slaves though, init as 0 int rate; while (true) { // invert the byte to be sent if (to_send == 1) to_send = 0; else if (to_send == 0) to_send = 1; Serial.print("Sending: "); Serial.println(to_send); digitalWrite(debug_led, to_send); rate = map(analogRead(5), 0, 1023, 0, 1000); software_serial.write(to_send); // send our byte out to the MAX485 delay(rate); } } |
This is the code for the slave Arduinos:
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#include <SoftwareSerial.h> int MAX485_Receiver_Output_PIN = 10; int MAX485_Driver_Input_PIN = 11; int MAX485_Driver_Output_Enable_PIN = 12; int debug_led_PIN = 9; SoftwareSerial software_serial (MAX485_Receiver_Output_PIN, MAX485_Driver_Input_PIN); // RX, TX void setup() { software_serial.begin(9600); // begin software serial pinMode(MAX485_Driver_Output_Enable_PIN, OUTPUT); digitalWrite(MAX485_Driver_Output_Enable_PIN, LOW); pinMode(debug_led_PIN, OUTPUT); } void loop() // run over and over { byte k; if (software_serial.available() > 0) // make sure there is something to read { k = software_serial.read(); // read in a single byte from the serial port digitalWrite(debug_led_PIN, k); } } |
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#include <SoftwareSerial.h> int MAX485_Receiver_Output_PIN = 10; int MAX485_Driver_Input_PIN = 11; int MAX485_Driver_Output_Enable_PIN = 12; int debug_led_PIN = 9; SoftwareSerial software_serial (MAX485_Receiver_Output_PIN, MAX485_Driver_Input_PIN); // RX, TX void setup() { software_serial.begin(9600); // begin software serial pinMode(MAX485_Driver_Output_Enable_PIN, OUTPUT); digitalWrite(MAX485_Driver_Output_Enable_PIN, LOW); pinMode(debug_led_PIN, OUTPUT); } void loop() // run over and over { byte k; if (software_serial .available() > 0) // make sure there is something to read { k = software_serial.read(); // read in a single byte from the serial port digitalWrite(debug_led_PIN, k); } } |
In subsequent posts, things will start getting more advanced. For now however this should be enough to start from scratch.
Thanks for reading.
The compiler reports an error in slavecode line 26.
(> 0) is not defined
Please help me, I can’t understand this.
Hey Karl
I think there may have been a problem with my code formatting system, try re-copying the code and trying again.
Devon
Hi,
My slave never get any message. I can see master does send message to slave.
how does the setup determine which one is master and which one is Slave. Does the master send only? and the slave receive only as well?
Master sends, slave receives. Everything is hard coded.
hi, I can’t see the schematic