OpenRB-150 library calls interfere with digital inputs

Technical Support
1

I’m using OpenRB-150 board with three XL430 servos and writing the code with Arduino IDE version 2.3.2. The board is powered from a high quality 60W 12V DC switching power supply. There is a switch between pin #1 (Arduino numbering) and GND. This is the test code:

#include <Arduino.h>
#include <OpenRB-150.h>

using namespace ControlTableItem;

constexpr uint8_t DXL_ID = 1;
constexpr float DXL_PROTOCOL_VERSION = 2.0;
constexpr int pin = 1; // Problem with pin 1

Dynamixel2Arduino dxl(Serial1, -1);


void setup() {
  Serial.begin(115200);
  pinMode(pin, INPUT_PULLUP); 

  // dxl.begin(57600);
  // dxl.setPortProtocolVersion(DXL_PROTOCOL_VERSION);
  // dxl.ping(DXL_ID);
  // dxl.torqueOff(0);

  delay(1000);
}


void loop() {
  Serial.println(digitalRead(pin));
  delay(100);
}

It behaves as expected when the dxl calls are commented as shown above. Unfortunately, when I uncomment them, the state of pin #1 is stuck at zero. Why is that?

I would expect an occasional zero reading due to noise, but not all readings at 0 when the switch is open. When I use an external 1K pullup resistor, the behavior is back to normal.

2

I have a feeling this might be a side effect related to the OpenRB not needing a dedicated TX/RX switching pin.

For our Arduino shields, pin 1 is used as the pin to switch between transmit and receive mode, but the OpenRB doesn’t need to use up an Arduino pin to do so. I wouldn’t be surprised if the backend code is still trying to occupy the pin in some way, does everything operate as expected with the external pullup resistor connected?

1 Like
3

Yes. 1K external pullup solves the problem. I also observed cyclical behavior on another floating pin with internal pullup: a few seconds low, a few seconds high.