Meeting Log Fall 2008
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September 25, 2008
H-bridges
An H-bridge is a four-transistor circuit that is often used for motor control. It is technically a DC-AC inverter circuit, but in practical robot applications the resulting "AC" output to the motor is such a low frequency it might as well be called switched DC. Depending on which of its inputs are active, an H-bridge can drive the motor forward or backward, let it coast, or stop it almost immediately.
Switching Regulators
Coop has written a good page on power supplies in general. I would urge you to check it out.
September 29, 2008
Tutorial: Blinky, a simple LED blinker
We started covering the basics of programming PICs in assembly. This is actually a large topic and will take several meetings to discuss. We created a simple LED blinker and experimented with changing the blink rate and blink pattern.
Demo
There was interest in constructing a larger dot-matrix LED sign, as inspired by the oh-so-blinky IEEE sign hanging in the office. An older one that Ben constructed several years ago was brought in and demonstrated.
October 2, 2008
Continuing our adventures with the PIC16F628A, we talked about interrupts.
Here is some sample code. The code rewrites the LED blinker of last meeting to use an interrupt-based timing scheme instead of using delay loops. This means that the microcontroller could do something in place of the delay loop if we wanted to -- interrupts are a way to emulate multitasking ability.
October 6, 2008
The major topic was button debouncing. We began writing a program to serve as a light sequencer, and we finished the code during the next meeting.
October 9, 2008
There was a walkthrough of the code produced on Oct. 6, and the mistakes were found and corrected. The working (but probably not optimal) code is here.
October 20, 2008
We looked at the basic use of analog-to-digital converters as well as using the MPLAB debugger.
For this meeting we used the PIC18F2420, since some of our PIC16F690 chips mysteriously stopped working. Sample code is posted here. The code initializes the analog to digital converter, selects Channel 0, and then conducts an endless stream of conversions. We relied on the debugger to view the result since it was a convenient segway into debugging.
October 23, 2008
We continued our look at ADC from the last meeting, then added table lookup to drive a seven-segment LED display directly from the microcontroller, completely bypassing any sort of decoder chip. The completed source code is here.
November 3, 2008
We discussed Pulse Width Modulation (PWM) during this meeting. An overview of pulse width modulation can be found here. For more details, particularly pertaining to software pwm: refer to our Software PWM page.
November 8, 2008
We enhanced our microcontroller programming knowledge by learning about the precision Timer Module found on most microcontrollers.
November 17, 2008
We continued work on our microcontroller project, a Persistence of Vision Device.
