Vernier Shield Hookup Guide

Contributors: bri_huang

Multiplexer

Vernier uses a variety of methods for identifying which sensors are connected to the interface. A majority of sensors use a resistor placed on one of the pins, but some of their sensors use I2C for both sensor identification and storing calibration data. The Vernier shield uses an analog multiplexer to share / route pins A4 (SDA) and A5 (SCL) to each of the four connectors.

Pins 10 (LSB) and 11 (MSB) are used to control the multiplexer. The following snippet of code illustrates one way to switch which connector A4 and A5 are connected to.

language:c
const int muxLSB = 10;
const int muxMSB = 11;

void setup()
{
  pinMode(muxLSB, OUTPUT);
  pinMode(muxMSB, OUTPUT);
}
void setMux(int connectorNum)
{ 
// void setMux(int connectorNum)
// connectorNum is a number from 0 to 3 which
// identifies which connector to switch the MUX to.
// Where if connector num is equal to:
//    0 --> Analog 1
//    1 --> Analog 2
//    2 --> Digital 1
//    3 --> Digital 2

  switch (connectorNum)
  {
  case 1: // ANALOG 2 - MUX ADDR 01
    digitalWrite(muxMSB, LOW);
    digitalWrite(muxLSB, HIGH);
    break;
  case 2: // DIGITAL 1 - MUX ADDR 10 
    digitalWrite(muxMSB, HIGH);
    digitalWrite(muxLSB, LOW);
    break;
  case 3: // DIGITAL 2 - MUX ADDR 11
    digitalWrite(muxMSB, HIGH);
    digitalWrite(muxLSB, HIGH);
    break;
  default: // ANALOG 1 - MUX ADDR 00
    digitalWrite(muxMSB, LOW);
    digitalWrite(muxLSB, LOW);
  }
}

In general, you won't need to access these lines unless you are interfacing to the Vernier sensors through I2C.