Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder

Circuit, current, resistor, electricity, electrical engineer, housing, Kirchhoff, Ohm, Ohm’s Law, resistance, voltage, wire

 Describe the relationship of a programmable thermostat to energy conservation.  Develop a model of the circuitry in a programmable thermostat.

 Describe how engineers use circuit diagrams to design a circuit.  List the advantages of using a breadboard during circuit design.

 1 breadboard  1 LM35 temperature sensor chip (Transistor: has 3 wires)  1 LM324AN operational amplifier integrated circuit  1 9-volt battery  1 9-volt battery holder  Ice  Ziploc bag

 Thermostat Worksheet  Breadboard and Circuit Diagram Basics Handout  1 jumper wire kit  Resistors  Multimeter

 Why might it be a good idea to be able to control at which temperatures a heater and/or air conditioner turns on and off?

 Today, we are going to investigate the circuit in a thermostat.  Does anyone know what a thermostat is?

 A thermostat is a device installed in homes and buildings to regulate the temperature of an area of the building — such as a single room, a few rooms (a zone), or the entire building.

 Thermostats are useful devices to regulate the temperature of a room, area or an entire building.  They work by using a temperature sensor — generally an electronic chip designed to change its resistance depending on the temperature.

 As the temperature of the transistor changes the amount of electricity it allows to move changes.

 The LM324 is the most common Operational amplifier used today. It was designed and introduced in 1974.

 The LM324 is 4 amplifiers in 1 chip!  Think about how a car has 4 speakers.  They take the input signal am boost it to make it more powerful.  Their function is by far more complex but for our purposes this is sufficient.

 Build the circuit as shown  Next slide shows same circuit from a different angle.

 This was because my fingers heated up the LM35.

 When using ice that you do not get water on the breadboard.  Do not puncture the ice bag.  Keep the ice and water in the bag.

 Do not connect the battery to the breadboard if you are not taking measurements.  Make sure resistors don’t touch one another.

 LEDs can easily burn out if they are left on too long, or if too large of a current is sent through them. This is why the output from the LM324AN goes through a resistance before reaching the LED. If a circuit is not working, and everything else seems to be in the correct place, try a different LED.

 Why is it important to completely close off all parts of the device except the outflow?