We are going to have the LED blink at about on and off on one second intervals (0.5Hz). Fan 1 will turn on at 46C temperature. Fan 2 will turn on at 60C temperature. To have some hysteresis both fans will turn off at 30C temperature.

Connect the Microchip MCP9700 temperature sensor up to input channel 1 on the smart servo controller.

• Pin 1 is +5v
• Pin 2 is Signal
• Pin 3 is 0V.

• Connect the LED to output channel 1. Add a 0.5K resistor between the LED and 0V. The resistor is to limit current through the LED.
• Connect the relays to outputs 2 and 3. Add free wheeling diodes across the relays to suppress back EMF.

Go to the IO Setup Tab,

• Set the channel 1 input to Analog.
• Set the output channels 1-3 to Outputs. Set the default state to -1 (off). This will keep the output at the current state even when no rules are active.

Create a new output state rule.

• Set the output state to -1 (Toggle).
• Create a condition to internally trigger every 1 second.

Create a new output state rule that will turn fan 1.

• Add a channel and set it to 2, set the value to 1. 1 is for true/on.
• Create a condition so that the rule will only be active when the temperature sensor is above 46C. From the data sheep for the sensor we calculate that 46C is 0.96 volts.

• Vout = Tc * Ta + V0C where
• Tc = 10.0mV/C
• V0C = 500mV
• Ta = Temperature
• Vout = Output voltage.

This step we are creating a rule that turns off the fans.

• Add an output state rule and add channels 2 and 3.
• Set the values for both to 0 for off.

Create a condition that only activates this rule when the temperature is below 30C. This works out to 0.80 V.

This is similar to how we turned on fan 1 except with a higher turn on voltage.

We are going to turn it on at 60C or 1.10 volts.

Now we program and test to make sure the circuit works the way we want it to.

• The LED should be blinking on and off every second.
• When we heat up the temperature sensor Fan 1 will turn on first.
• As temperature increases Fan 2 will then turn on.
• When we remove the heat source both fans will turn off when the temperature falls below the threshold.

Check out the youtube video for a demonstration of this in action

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Thanks,

Mark