ECE 332L
Microprocessors Lab Lab 8
Spring 2008
PWM and DC Motor
Objective:
Pulse-Width Modulation (PWM) and DC Motor.
Note: A new Nios II processor core has been generated that provides 2 PIO based interfaces to the hardware. You
need to change Nios II IDE system library property (includes Timestamp timer, Program memory (.text), Read-
only data memory (.rodata), Read/write dta memory (.rwdata), Heap memory, and Stack memory), see figure on
the last page. The interface to the Digilent PmodHB3 H-Bridge is through a 40-pin connector (JP2). The
PmodHB3 H-Bridge module drives the DC motor. In addition, 4 AAs or AAAs batteries are used to power the
DC motor. Some details of the DC motor are included in the following figure.
Tamiya 70093 3-Speed Crank Axle Gearbox
This compact gearbox gives you options for gear ratios of 17:1, 58:1,
and 204:1.
The motor is rated for 3 volts but will typically work fine up to 6 volts.
When using this product with the dual serial motor controller (or any
motor driver based on an H-bridge), keep in mind that up to a few
volts (depending on the load) are lost on the transistors of the H-
bridge, so that a 4.5 volt battery delivers about 3 volts to the motors,
giving them a reasonable amount of power. Motor overheating can be
caused by excessive stalling, even at very low voltages.
http://www.technobots.co.uk/acatalog/info_1452_004.html
The documentation (Digient PmodHB3, 2A H-Bridge Reference Manual, Revision: February 26, 2007, Doc: 502-
069) for the H-Bridge is supplied on class web site.
During development cycles, the hardware to be controlled might not be available yet or can be easily damaged.
To accommodate these situations, code development can be carried out with the use of a test platform. Upon
completion of code development on the test platform, the code can be migrated to the final hardware with minor
changes.
Since the H-Bridge hardware used in this lab can be easily damaged and batteries can be quickly run down, this is
a good case to use a test platform. The test platform in this case is a set of LEDs that visually represents the PWM
state. You can utilize 10 LEDs to represent the full period and activate the number of LEDs (using buttons) to
represent the ON duty cycle (one LED ON as 10% duty cycle or five LEDs ON as 50% duty cycle).
Important: You need to show your design to the lab instructor before you are permitted to use the DC motor
hardware setup.
Intermediate Deliverables:
1. Develop routine that lights one LED for the required ON duty cycle and are off for the remainder of period.
Provide switch or button that enables or disables display of LED.
2. Extend first routine to display level bar that is progressively lit to maximum value specified by duty cycle and
remaining LEDs are unlit. Provide buttons to increase or decrease duty cycle.
3. Add functionality that reverses direction of progress bar. Use switch or button.
