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Topic: Multiple I2C sensors on a single Arduino Uno (Read 2713 times) previous topic - next topic


There are a few threads I've looked at before, but all of them seem to have a slightly different scenario and I can't apply it. So I will ask for help with my case.

I have a TSL2561 Luminosity sensor and a BMP180 Pressure sensor. I want to connect and read both simultaneously.

I connected the TSL2561 to the pins labelled SDA and SCL on the Arduino uno board. It works fine with the libraries and sample program provided by Adafruit.
However, when I connect the BMP180 to the same pins on the board while the TSL2561 is also attached. Only the TSL2561 works.
I tried using libraries and sample program provided by Sparkfun (as adafruit doesn't seem to have any) and my BMP180 didn't work, for whatever reason.

And instead of explaining other things I've tried, could someone outline to me how would I connect those 2 sensors to a single arduino uno board and have them working at the same time?



Hi xmaxer

Is it the Adafruit breakout boards that you are using, for both devices?

Adafruit have a TSL2561 tutorial and library here:  https://learn.adafruit.com/tsl2561/overview

Does the BMP180 work when only it is connected to the Arduino?

Have you connected 3.3V and GND from the Arduino to both breakout boards, as well as SCL and SDA?


Hackscribble.  Writing about making things



I am using these specific ones:

Yes, I connected both to the same 3.3V and GND, and both to the same SDA/SCL pins on the board.

What's really weird, is with the BMP180, when I try and use it. It gets stuck on after printing 'REBOOT'
(You'll understand where, when you see the code)
Code: [Select]
/* SFE_BMP180 library example sketch

This sketch shows how to use the SFE_BMP180 library to read the
Bosch BMP180 barometric pressure sensor.

Like most pressure sensors, the BMP180 measures absolute pressure.
This is the actual ambient pressure seen by the device, which will
vary with both altitude and weather.

Before taking a pressure reading you must take a temparture reading.
This is done with startTemperature() and getTemperature().
The result is in degrees C.

Once you have a temperature reading, you can take a pressure reading.
This is done with startPressure() and getPressure().
The result is in millibar (mb) aka hectopascals (hPa).

If you'll be monitoring weather patterns, you will probably want to
remove the effects of altitude. This will produce readings that can
be compared to the published pressure readings from other locations.
To do this, use the sealevel() function. You will need to provide
the known altitude at which the pressure was measured.

If you want to measure altitude, you will need to know the pressure
at a baseline altitude. This can be average sealevel pressure, or
a previous pressure reading at your altitude, in which case
subsequent altitude readings will be + or - the initial baseline.
This is done with the altitude() function.

Hardware connections:

- (GND) to GND
+ (VDD) to 3.3V

(WARNING: do not connect + to 5V or the sensor will be damaged!)

You will also need to connect the I2C pins (SCL and SDA) to your
Arduino. The pins are different on different Arduinos:

Any Arduino pins labeled:  SDA  SCL
Uno, Redboard, Pro:        A4   A5
Mega2560, Due:             20   21
Leonardo:                   2    3

Leave the IO (VDDIO) pin unconnected. This pin is for connecting
the BMP180 to systems with lower logic levels such as 1.8V

Have fun! -Your friends at SparkFun.

The SFE_BMP180 library uses floating-point equations developed by the
Weather Station Data Logger project: http://wmrx00.sourceforge.net/

Our example code uses the "beerware" license. You can do anything
you like with this code. No really, anything. If you find it useful,
buy me a beer someday.

V10 Mike Grusin, SparkFun Electronics 10/24/2013

// Your sketch must #include this library, and the Wire library.
// (Wire is a standard library included with Arduino.):

#include <SFE_BMP180.h>
#include <Wire.h>

// You will need to create an SFE_BMP180 object, here called "pressure":

SFE_BMP180 pressure;

#define ALTITUDE 1655.0 // Altitude of SparkFun's HQ in Boulder, CO. in meters

void setup()

  // Initialize the sensor (it is important to get calibration values stored on the device).

  if (pressure.begin())
    Serial.println("BMP180 init success");
    // Oops, something went wrong, this is usually a connection problem,
    // see the comments at the top of this sketch for the proper connections.

    Serial.println("BMP180 init fail\n\n");
    while(1); // Pause forever.

void loop()
  char status;
  double T,P,p0,a;

  // Loop here getting pressure readings every 10 seconds.

  // If you want sea-level-compensated pressure, as used in weather reports,
  // you will need to know the altitude at which your measurements are taken.
  // We're using a constant called ALTITUDE in this sketch:
  Serial.print("provided altitude: ");
  Serial.print(" meters, ");
  Serial.println(" feet");
  // If you want to measure altitude, and not pressure, you will instead need
  // to provide a known baseline pressure. This is shown at the end of the sketch.

  // You must first get a temperature measurement to perform a pressure reading.
  // Start a temperature measurement:
  // If request is successful, the number of ms to wait is returned.
  // If request is unsuccessful, 0 is returned.

  status = pressure.startTemperature();
  if (status != 0)
    // Wait for the measurement to complete:

    // Retrieve the completed temperature measurement:
    // Note that the measurement is stored in the variable T.
    // Function returns 1 if successful, 0 if failure.

    status = pressure.getTemperature(T);
    if (status != 0)
      // Print out the measurement:
      Serial.print("temperature: ");
      Serial.print(" deg C, ");
      Serial.println(" deg F");
      // Start a pressure measurement:
      // The parameter is the oversampling setting, from 0 to 3 (highest res, longest wait).
      // If request is successful, the number of ms to wait is returned.
      // If request is unsuccessful, 0 is returned.

      status = pressure.startPressure(3);
      if (status != 0)
        // Wait for the measurement to complete:

        // Retrieve the completed pressure measurement:
        // Note that the measurement is stored in the variable P.
        // Note also that the function requires the previous temperature measurement (T).
        // (If temperature is stable, you can do one temperature measurement for a number of pressure measurements.)
        // Function returns 1 if successful, 0 if failure.

        status = pressure.getPressure(P,T);
        if (status != 0)
          // Print out the measurement:
          Serial.print("absolute pressure: ");
          Serial.print(" mb, ");
          Serial.println(" inHg");

          // The pressure sensor returns abolute pressure, which varies with altitude.
          // To remove the effects of altitude, use the sealevel function and your current altitude.
          // This number is commonly used in weather reports.
          // Parameters: P = absolute pressure in mb, ALTITUDE = current altitude in m.
          // Result: p0 = sea-level compensated pressure in mb

          p0 = pressure.sealevel(P,ALTITUDE); // we're at 1655 meters (Boulder, CO)
          Serial.print("relative (sea-level) pressure: ");
          Serial.print(" mb, ");
          Serial.println(" inHg");

          // On the other hand, if you want to determine your altitude from the pressure reading,
          // use the altitude function along with a baseline pressure (sea-level or other).
          // Parameters: P = absolute pressure in mb, p0 = baseline pressure in mb.
          // Result: a = altitude in m.

          a = pressure.altitude(P,p0);
          Serial.print("computed altitude: ");
          Serial.print(" meters, ");
          Serial.println(" feet");
        else Serial.println("error retrieving pressure measurement\n");
      else Serial.println("error starting pressure measurement\n");
    else Serial.println("error retrieving temperature measurement\n");
  else Serial.println("error starting temperature measurement\n");

  delay(5000);  // Pause for 5 seconds.

This sample program worked when the BMP180 is connected to the A5/A4 analog pins on the board ALONE (ie: no other sensors connected to the board in any way)

When I added the lux sensor to the board to the SDA/SCL pins. The lux sensor worked when tested with it's own standalone program. However, the BMP180 no longer worked as it just got stuck after printing 'REBOOT'. Then I decided to connect the BMP180 to where the lux sensor is connected to (The SDA/SCL pins) and the results where exactly the same, the Lux sensor worked. But not the BMP180.

Thanks for taking the time to help out.


Here's an outside chance that may be worth investigating ....

It looks like both of those both of those boards have 10K pullup resistors on the SDA and SCL lines.  When both boards are connected simultaneously the effective pull-up is 5K which shouldn't be a problem.

Perhaps the TSL2561 is happy with this situation and the BMP180 is not.  You can test this out by running the BMP180 alone and getting it to work as you said it did before.  Then add a pair of external 10K pull-ups to those two lines and see if it still works.

Of course if you already have external pull-ups on those lines then removing them will probably solve your problem.



Right so, resistance problem. I get the first part, but don't know what you mean by adding a pair of 10k resistors to those two lines. Is there any illustration I could get to understand better?

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