Getting the sensor id

Squirrel Code
1

Hi,

I’m using the “multiple devices” part of this https://electricimp.com/docs/resources/onewire/ for my device code. I’m connecting 3 sensors and it’s working perfectly.
I now need to write the agent side and will need the readings for each sensor’s serial and temperature.
These details are in line 151:
server.log(format(“Device: %02d Family: %02x Serial: %02x%02x%02x%02x%02x%02x Temp: %3.2f”, (device + 1), slaveId[7], slaveId[1], slaveId[2], slaveId[3], slaveId[4], slaveId[5], slaveId[6], tempCelsius));

But I’m not sure how to pass the 6 readings (serial and tempCelsius for the 3 sensors) to the agent.
Would appreciate your help with how to code this please.

Thanks,
Perla

2

Create an array to hold the data to be sent to the agent (this would be at the start of your device code):

`data <- [];`

Later, loop through each of your three sensors in turn

`// Create a sensor entry as a table
local sensor = {};

// Add an 'ID' key to hold a device's serial number as a string
sensor.ID <- format("%02x%02x%02x%02x%02x%02x", slaveId[1], slaveId[2], slaveId[3], slaveId[4], slaveId[5], slaveId[6]);

// Add the temperature data
sensor.temperature <- tempCelsius;

// Add sensor to the data array
data.append(sensor);`

After the loop, send the data array to the agent:

agent.send("incoming.data", data);

In your agent code, you will need to register a function to handle the incoming data:

`device.on("incoming.data", function(info) {
    // 'info' is an array containing three tables
    foreach (sensor in info) {
        server.log("Sensor " + sensor.ID + " reports a temperature of: " + sensor.temperature + "C");
   }
}`

This code just logs the data received from the device, but you’ll see how it can be extended to tweet the data, relay it to a web service like Xively or hold on to it until a mobile phone app requests the current data.

3

Thanks smittytone for your help! it works perfectly…

I have another question regarding the same code please. So, I tested it indoors it works perfectly but outdoors with temperature that can go down to -20 the temperature returned for the sensors is around 4093! And i have one measuring the soil temperature, it’s almost fixed on 0.37! Is it something related to the hardware or can it be fixed with the code?

Thanks

4

Look at the datasheet for your sensor and see what the specifications are. Maybe you are at the lowest temp limit possible?

I live in Minnesota, and I quit working at that temperature too :frowning:

5

hahaha…
It should be –55°C to +125°C, this is why I thought to check the software side…

Check this out:

This is for Netduino but with similar concept, please check the comments part under
Brad BerklandMarch 23, 2013 at 1:57 PM

What do you think?

Thanks for your support.

6

The temp only goes bad below -20, or any negative number?

If you look at this file:

Notice Table 1.
When temps are negative, it applies 2’s complement.

So, when the temp outside is -20, it will be around 4000.

Here is a simpler example of what happens with negative numbers & 2’s complement

5 … 0000 0101
4 … 0000 0100
3 … 0000 0011
2 … 0000 0010
1 … 0000 0001
0 … 0000 0000
-1 … 1111 1111
-2 … 1111 1110
-3 … 1111 1101
-4 … 1111 1100
-5 … 1111 1011

What complicates your sensor is that is can have different resolutions 9,10,11 or 12 bits. So they make bits 11-16 sign bits.

If your hex to decimal value is less than 2048, your temp is positive.

If your hex to decimal value is 2048 or higher, you have a negative temp.

Bitwise, you mask it with FFFF using XOR (exclusive OR) and add 1.

0000 1010 0010 = +10.125C Decimal 162

1111 0101 1110 = -10.125C Decimal 3934

1111 0101 1110
1111 1111 1111 XOR with FFFF

0000 1010 0001

Now add 1

0000 1010 0010

See, it is now the same as +10.125

But you know it is negative because it was greater than 2048

7

Perfect!. Thanks