ELE4
Control Systems
Revision Notes
• Open Loop - No feedback
• Closed Loop - Feedback
• Negative
- Reduces the effect of the input
- Output reaches an adjustable steady end point
• Positive
- Increases the effect of the input
- Output oscillates or saturates
Contents
• Hunting
• Hysteresis
Contents
Contents
| RAM | Memory Mapping |
| ROM | I/O Mapping |
| Port | Read |
| Processor | Write |
| Clock | Volatile |
| Bus | Interrupt |
| Data Bus | Bit |
| Address Bus | Byte |
| Control Bus | Word |
Contents
• PIC/AVR
• RISC
• Harvard Architecture
- Separate Instruction Bus
• Advantages
- Cheap
- Adaptable
Contents
• Used to determine the sequence of operations required.
• Aids logical thought.
Contents
• PRINT
• INP
• OUT
• REM
• END
• DIM
• DO – LOOP – WHILE/UNTIL
• FOR – NEXT - STEP
• IF – THEN – ELSE
• GOSUB – RETURN
• INKEY$
• INPUT
• CLS
• GOTO
Contents
• Integer - %
• Real
• String - $
• Arrays
Contents
• Comparison with PC
- NN processors very simple but very many used, traditional computer processors very complex but only a few used.
- NNs retain data in the weightings of the connections made, computers have dedicated memory components.
- NNs are trained - changing the weightings of the connections made with experience, computers follow a pre-described set of instructions.
- NNs best at predictive tasks, computers better at calculations.
Contents
- Three states – 0, 1, open circuit
- Enables data to be put onto a data bus without causing ‘bus contentions’
- Output Enable (OE) often ‘active low’
- One needed per bit
Contents
- Enables data to be outputted from data bus.
- Processor sets valid data onto data bus and then pulses CK high.
- Data captured and stored in latches.
- One flip-flop needed per bit.
Contents
R7 = Rf,
R6 = 2Rf,
R5 = 4Rf,
R4 = 8Rf,
R3 = 16Rf,
R2 = 32Rf,
R1 = 64Rf,
R0 = 128Rf
- Usually connected to data bus via a latch.
Contents
• Digital Ramp ADC
- Computer increments output from DAC until the analogue voltage is greater than the analogue input voltage.
- Comparator detects this and ACK is pulled low.
- Computer detects this and so the last number it sent to the DAC is equivalent to the analogue input voltage.
Contents
• Very fast.
• Many comparators
- 2n-1
• Expensive
• Uses:-
- Video
- Digital Oscilloscopes
Contents
• Base address usually &H378.
Contents
• Two switching points.
- Hysteresis
- Reduces false switching on noisy signals.
• Consider as a comparator with a variable reference voltage.
• Calculate the voltage at P when the output is high.
- This gives the upper switching point.
• Calculate the voltage at P when the output is low.
- This gives the lower switching point.
Contents
• Resolution:-
- 360/2n degrees
- n = number of rings.
• 360/s degrees.
- S = number of slots.
• Optical Shaft Encoder.
- Angular direction, speed and absolute position.
• Slotted Disk (with one sensor).
- Angular speed and relative position.
Contents
• Remember LED calculations often included in these questions!
• Photodiodes:-
- Can produce a small voltage – 0.6V
- Often used in reverse bias mode
- Reverse bias current proportional to incident light
- Very fast response time (LDRs are very slow)
Contents
• Rotates through a precise angle.
- 7.5° for 4 pole motor
- 1.8° for 6 pole motor.
• Needs control electronics to continuously rotate.
- Current applied in turn to each set of coils.
• Less torque and speed of rotation than traditional motor.
Contents
• Seven LEDs for segments plus one for the decimal point.
• Combinations lit to display numbers and characters.
- E.g. a, b, g, c, d for 3
• Standard calculations apply to each LED (segment).
Contents
• Multiplexed display.
- Only one column powered at any one time.
- Relies on persistence of vision.
- Can be dimmer than normal display since each column is only illuminated for 1/5th of the time.
• LEDs to be lit are selected via the Row connections as each Column is powered.
Contents