2nd SHT15 Humidity/Temp. Sensor to Arduino

Archive SparkFun Site Questions/Comments
1

Hi, all.

I’ve been quite satisfied with the SHT15 and Arduino interfacing using the software example shown in SFE site.

One newbie question:

For the first set of SHT15 humidity/temp sensor, 10K resistors are used for pull-ups.

Would the pull-up resistors be needed for the second set of SHT15 sensor? Or shouldn’t I use the pull-ups?

I’m not positively sure but, in the case of normal I2C, the second set does not use the pullups.

The reason I’m asking is that the SHT15 is not based on I2C but on two wire interfacing.

Thanks for your interests.

2

You only should use one pair of pull-ups per I2C bus. So, when connecting several SHT1x together, you only need one set.

3

2-wire is just another name for I^2C - its just a way to do an end run around Phillips trademark on the name.

Cheers,

–David Carne

4

Hi,

I’m so happy to hear that I shouldn’t add pull-ups for the second and so forth.

Soldering those teeny-tiny SMD resistor chips made my eyes sore even with the maginifiers. Well, that was my first SMD soldering experience. After that experience, I think I might manage the soldering jobs somehow.

Thank you again. :slight_smile:

5

You either get used to it, or buy a microscope :slight_smile:

6

Thanks all,

Btw, I just remember that Sensirion(SHT15) says that SHT15 does not follow the exact I2C of Philips but a sort of Two Wire, which makes the Arduino program longer(I really appreciate the contributions of Maurice, Wayne, and many other kind programmers).

Well, then I might not be able to use the same pins for the 1st sensor and 2nd sensor(SDA and SCL).

Thank you again.

7

Unfortunately, the SHT15 is hardcoded at address 0 so you can’t put multiples on one bus. You can have a single SCL and multiple SDA (one per chip). Just make sure SDA is hi on all but the one you are talking to.

BTW, you only need a resistor on SDA as SCL is always driven from the micro. The SHT15 can’t be a master.

To save yourself some headaches, I would wire it up to two GPIO pins and not use the micro’s built-in I2C hardware. Also, remember that it takes up to 320ms to take a measurement. I ended up having the processor look for the measurement to be done in a timer ISR so it wouldn’t get stuck in a spin loop waiting.

8

Did you succeed? I’m working on the same problem (integrating a second SHT) and could use some help, bc I can’t figure out the right code…

It would be great if you could provide some code!

Thanks

Milarepa