Week 10, Tuesday

Week 10 Wednesday -- MAE 412

Lecture:

Optical Proximity Detector Circuit -- potential problem -- missed events from too low a sampling frequency -- don't forget that the ISR suspends the USER program for 8.3 msec every 41.5 msec.
Solution -- /R/S Flip-Flop -- truth table
Aside: SPDT Switch Debouncer using /R/S Flip-Flop
Hall Effect Sensor -- Schmitt-trigger input / open collector output
Point-to-Point Trolley Control using Diodes
Polarity reversal using DPDT relay or switch
Mechanical Sensors / Limit Switches
Rule 17 - "... All devices should be disabled when I/O port lines are high (true)." Why?
Rule 13 - "Control circuits involving track power (20 VAC) must be electrically isolated from computer and logic circuits (5 VDC) using OPTO-ISOLATORS." Please note that separate DC power supplies are not permitted. If you need 12-20 VDC you should get this by rectifying the track voltage while being careful not to draw power during a DATA FRAME -- see Rule 10 below. Additional power packs (9VDC unregulated) are permitted. These may be needed for powering Servo Motors or other high current devices.
Rule 10 - "In general, power is not to be extracted from the railroad tracks during a DATA FRAME. The exception to this rule is in the powering of low-current and electrically-quiet devices such as LEDs and lamps." How to test for Power Draw during DATA FRAME?
Auxillary Power Supply circuit for operating devices that require 12-20 VDC.
Model Airplane Position Servo

Assignments and Reference Material:

For information about the Interrupt Service Routine read Chapter 5 on Communications by Gurion and Simon in Volume 1 of the On-line Text.
For information about the Bar-Code Reader, RR Signal Control, and Interlocking Control (Track Kill) read Chapter 6 on Block Management by Lecky and Fiderer in Volume 1 of On-line Text.
Read Chapter 2 of Volume 1 of the On-line Text ("Hornby Railways ...")
Document your working computer using ORCAD (see example on CIRCUITS page) -- Hand in next Tuesday (include 74LS244 buffer).
Read Chapter 3 of CST -- available on-line (go to BLACKBOARD => LIBRARY => e-reserves => authentication page => user:mae412 password:littman1). Continue studying the 6502 instruction set.