Single-phase alternating current motors are typically found in household items such as fans, and their speed can be easily controlled when using a number of discrete windings for set speeds. In this project, we build a digital controller which allows users to control functions such as motor speed and operating time. This project also includes an infrared receiver circuit that supports the NEC protocol, where a motor may be controlled from push buttons or from a signal received by an infrared transmitter.
To carry this out, a GreenPAK™ SLG46620 IC is used as a basic controller in charge of these diverse functions: a multiplex circuit to activate one speed (out of three speeds), 3-period countdown timers, and an infrared decoder to receive an external infrared signal, which extracts and executes a desired command.
If we look at functions of the circuit, we note several discrete functions simultaneously employed: MUXing, timing, and IR decoding. Manufacturers often use many ICs for building the electronic circuit because of the lack of an available unique solution within a single IC. Use of a GreenPAK IC enables the manufacturers to employ a single chip for including many of the desired functions and consequently reduce the system cost and oversight of manufacturing.
The system with all its functions has been tested to ensure proper operation. The final circuit may require special modifications or additional elements tailored to the chosen motor.
To check that the system is operating nominally, test cases for the inputs have been generated with the help of the GreenPAK designer emulator. The emulation verifies different test cases for the outputs, and the functionality of the IR decoder is confirmed. The final design is also tested with an actual motor for confirmation.
1. 3-Speed AC Fan Motor
3-speed AC motors are single-phase motors operated by an alternating current. They’re often used in a wide variety of household machines such as various types of fans (wall fan, table fan, box fan). Compared to a DC motor, controlling speed in an alternating current motor is relatively complicated since the delivered current's frequency must change in order to change the motor speed. Appliances such as fans and refrigeration machines usually do not require fine granularity in speed, but require discrete steps such as low, medium, and high speeds. For these applications, AC fan motors have a number of built-in coils designed for several speeds where changing from one speed to another is accomplished by energizing the desired speed's coil.
Figure 1: 3-Speed AC Wall Fan Motor
The motor we use in this project is a 3-speed AC motor that has 5 wires: 3 wires for speed control, 2 wires for power, and a start capacitor as illustrated in the Figure 2 below. Some manufacturers use standard color coded wires for function identification. A motor’s datasheet will show the particular motor’s information for wire identification.
Figure 2: Motor Wiring Diagram
2. Project Analysis
In this project, a GreenPAK IC is configured to execute a given command, received from a source such as an IR transmitter or an external button, to indicate one of three commands:
On/Off: the system is turned on or turned off with each interpretation of this command. The state of On/Off will be reversed with each rising edge of the On/Off command.
Timer: the timer is operated for 30, 60, and 120 minutes. At the fourth pulse the timer is turned off, and the timer period reverts to the original timing state.
Speed: Controls the speed of the motor, successively iterating the activated output from the motor’s speed-selection wires (1,2,3).
3. IR Decoder
An IR decoder circuit is built to receive signals from an external...Read more »