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You are here: EK2100 Examples > Multicasting a Command

Multicasting a Command

IoT devices work best when they're able to respond without human intervention, so lets build a temperature sensor with an alarm.

Connecting a Thermistor to the Protoboard

This exercise will use a protoboard setup from the Sounding an Audible Alarm exercise. If you need to, take a moment to check it out and make sure your protoboard is assembled correctly. Don't worry, we'll wait.

ClosedTo connect the thermistor:
  1. You'll first need to connect a resistor (blue) to the SN171 protoboard. Bend the legs of the resistor toward one another as seen in the picture. Place one resistor leg into the terminal block labeled GPIO 18 (located on the upper right-hand side of the SN171 protoboard.)
  2. Place the other leg into the connector labeled VCC. (Located in the center of the right-hand side.) There is no polarity on a resistor, so it does not matter which leg you choose for which pin. Note that there are two terminals labeled VCC. You could use either of them here, but for clarity we recommend you use the one between GPIO 14 and GPIO 15.
  3. Tighten the screw for the VCC pin only. This should lock the one leg of the resistor in place. We’ll address the other leg in a moment. (Déjà vu?)
  4. You'll next connect the thermistor to the SN171 protoboard. Place one leg of the thermistor (see picture for identification) into the spot labeled GPIO 18 (don’t worry: it is supposed to share the connector with the resistor) and the other leg in the first slot in the connector. (The GND pin.) There is no polarity on the thermistor, so it does not matter which leg you choose for which pin. Again, a picture is worth some number of words, so please refer to the figure for how the setup should look. Notice how you have to bend the legs of the thermistor to reach across several connector slots.

    Tighten the associated screws.
  5. Reconnect the power to the SN171 protoboard.

Hold the thermistor between your thumb and forefinger to raise the temperature. (If you have especially cold hands, it may be necessary to warm your hands first, or to rub the thermistor to warm it up. You may also blow over the thermistor to warm it up.) Once it reaches a pre-set threshold it will trigger a 5 second timer. The start of the timer will be indicated by the green LED on the SN171 protoboard and the flashing amber LED on the SN132 SNAPstick.

The buzzer will sound once the timer expires unless the alarm cut-off is executed. This can done one of two ways:

  1. Executing the alarmCutOff() function in the “TemperatureAlarm2XX” specific section of the Node Info pane within Portal. (This can be done on either node.)
  2. By pressing the built-in SN171 protoboard button.

A quick “chirp” of the buzzer will indicate that the alarm is bypassed. (Much like the “chirp” of a car alarm.)

ClosedWhat just happened?

The strength of the Internet of Things is that it provides a means for monitoring things in ways that would not be possible for a human. A SNAP node can tirelessly monitor a sensor for a condition, and when that condition is met, it can respond in multiple ways. In this example, the node sounded an audible alarm, but that might be just one part of the response. It could just as easily sound a buzzer, send an email, and shut off a valve, all in rapid succession.

This is where we can see the strength of a "sense and respond network". It's helpful to get an email telling you something is wrong. It's better to get an email telling you that something WAS wrong, and measures were put into place to limit harm.