Spark Core and DS18B20 Digital Temperature Sensor

Getting Started
21

I come from some basic Arduino coding and I tried the spark-dallas-temperature.h and OneWire.h (thanks @krvarma for the great work!)
I was able to read eight ds18b20 (and send the data to Gdrive, thanks @binaryfrost), but I did it without a direct reference to the sensor serial number as I was able to do with the Arduino’s library (DallasTemperature.h).

Below is the piece of code for Spark (100* is to bypass the limitation on the float). Everything works, but I would like to be sure that each variable “temperature …” always refers to the same sensor, while if one sensor stops working, I see -12700 as “temperature8” , but I do not know which sensor is not working anymore.

sensor.requestTemperatures();
temperature1= 100sensor.getTempCByIndex(0);
…
temperature8= 100sensor.getTempCByIndex(7);

In Arduino I was referring to the serial number of each sensor, see below.
I tried a bit with the Spark, but I couldn’t figure out how to do it.

DeviceAddress insideThermometer = { 0x28, 0xB8, 0x15, 0xCE, 0x04, 0x00, 0x00, 0xA4 };
…
sensors.requestTemperatures();
float tempCin = sensors.getTempC(insideThermometer);

P.S. I also had a look at the other discussione OneWire Temperature Publish Example with Multiple Sensors, but most probably the issue I’m facing can be easily addressed with the spark-dallas-temperature.h

22

The sample code seems to be configured for parasite mode:
ds.write(0x44); // start conversion, with parasite power on at the end

Is there a specific change needed for non-parasite mode?

23

Figured it out
ds.write(0x44, 1); // is for parasite mode
ds.write(0x44); // is for non-parasite mode

The problem I was having was answered a little higher up
present = ds.reset();
ds.select(addr);
ds.write(0xBE, 0); // Read Scratchpad 0
ds.write(0x00,0); // Recall Memory 0 <--------ERASE THIS LINE

1 Like
24

Did you ever finalize the OneWire library? I’d like to hook up some DS18B20’s.

25

Have you looked in the web IDE (the “Launch” button on Spark.io) for libraries? I think there is more than one available now.

1 Like
26

Thank you very much - just what I was looking for.

27

I setup a network to do temperature monitoring using 5 DS18B20s connected to the 2 unused lines on my POTS land line. Your phoneline is probably 4 wire and each landline only uses 2 of them. So - you have jacks already in your house and you won’t have to run new wiring to each room.
It worked well with a run approx 200 feet long.

Make sure (of course) to disconnect the lines at the TelCo box.

1 Like
28

That’s a pretty sweet idea.

I have considered using them for a CANbus so small modules could communicate around the house. But now with how cheap the photon is, it’s hardly worth the trouble.

29

Hi, Your code works for me. But: how about negative celsius?

30

Re my previous reply: I was asking “bko June '14”, above.

31

Hi @rch

Are you having trouble with negative values or are you just asking? The code uses int16_t, a 16-bit signed type to hold the results from the 18b20, which sign-extends its result to 16-bits. So I think negative values are handled properly.

What are you seeing?