Club Light Controller
           By: Alex Cerruti and Chris Wherry
               EE476 -- Spring 2002

Hardware Design  

Figure 1:  Full Wave Bridge Rectifier—Main Power Source

Every circuit begins with the power source.  In our CLUB Light, we had a conveniently available transformer that stepped the line voltage (120 VAC) to 12 VAC.  This voltage was fed into a full wave bridge rectifier, and a 100 mF polarized capacitor was used to minimize the unregulated output voltage.  From this point, all necessary regulated voltages were created using voltage regulators.

Figure 2:  The Atmel 90S8515 Microcontroller Unit and its associated ports


A single 5-volt regulator was used to power the MCU alone, for fear of mixing digital noise into the analog interfacing circuits.  Additionally, all outputs and inputs were buffered from the analog circuits to minimize noise. 


Figure 3:  The Temperature Sensor (top half) and Beat Detector (bottom half)  

The heart of the temperature sensor is the LM34 temperature sensor.  It provides a linear output voltage of 10 mV/°F.  The output voltage from the LM34 is then gained by a factor of 2 using the leftmost, top opamp in a non-inverting configuration.  The opamp immediately following it is used as a comparator, with the trigger voltage set at a temperature corresponding to about 90°F (keeping in mind the gain of 2 from the previous stage).  When the temperature of the sensor exceeds 90°F, the output of the comparator goes high (+5 volts).  Finally, this signal is sent into a 2N3904 transistor, which pulls the pin voltage on PIND.7 low when the temperature exceeds 90°F, instructing the MCU to turn on the cooling fan.  

The audio input receives a line-level input (typically 2 Volts peak).  The very first opamp is a Sallen-Key 2nd order Butterworth Low Pass filter with cutoff of about 250 Hz.  This filter was used for its nice attenuation characteristics.  The output of the filter (only the positive excursions of the audio signal) is then fed into the second opamp that gives a gain of 2, and its output is passed through a diode.  The capacitor in parallel with the resistor to ground acts as a filter, increasing the amount of time it takes for the voltage to decay on the input of the third opamp, a comparator.  The comparator is set to trigger at 2.5 volts, and its output is again fed into a 2N3904 transistor to interface it to PIND.6 of the MCU (admittedly, a Schmitt Trigger would probably work better here, with a rising edge trigger of 4 volts, and a falling edge trigger of 1 volt or less).  The MCU then polls for a random number (using software) and changes the color wheel accordingly.


Figure 4:  Fan and lamp driver interface circuits

The fan and lamp driver interface circuits are simply used to easily control these devices and to isolate the MCU from high voltages.  When a high voltage is output onto PINC.2, the TIP31-C will sink current and the fan will turn.  The TIP31-C isolates the MCU from back EMF induced by the stators in the fan motor.  A 12-volt DC voltage regulator supplies the power to the fan.  Similarly, a 2N3904 controls the relay, which turns the lamp on or off.  A smaller transistor could be used for the lamp relay because a large sink current was not required.


Figure 5:  Motor driver interface circuit

The motor driver interface circuit is very similar to the fan driver interface circuit.  A 12-volt voltage regulator provides the power to run the stepper motor (it draws 200 mA of current, continuously).  The TIP31-C is capable of providing the required current to the stator windings, and additionally, they isolate the MCU from back EMF.  It should be noted that at all times the light is on, this circuit draws power, which it uses to lock the axle in place when the color wheel is not spinning.  The motor spins by receiving signals from the MCU.  For example, in order to make the motor spin clockwise as seen in the schematic above, the ports would have to be successively pulsed in a periodic sequence:  turn on PINB.3 for 5 msec then turn it off, turn on PINB.2 for 5 msec then turn it off, turn on PINB.1 for 5 sec then turn it off, turn on PINB.0 for 5 msec, then turn it off, turn on PINB.3 for 5 msec then turn it off….  Every time a period is cycled (from PINB.3 to PINB.0) the motor turns 1/5 of the distance to the next color.  Hence, five periods are required to rotate the stepper motor to the next color from the previous color.  The same sequence, but in reverse order, is used to spin the motor counter-clockwise.