A PIC, or peripheral interface controller, is a microcontroller: a small computer on a single chip. A PIC holds a processor, program memory, data memory and input/output pins.

Name a commonly used PIC with digital I/O only and one with analogue inputs.

The PIC16F84A has digital input and output pins only. The PIC16F88 adds analogue inputs through a built-in 10-bit ADC.

Explain how a PIC can provide closed loop temperature control.

A thermistor divider feeds an analogue input, and the program compares the reading with a set value. The PIC switches the heater on below the set value and off above it.

Why does on/off control with a single set point cause rapid switching, and how can a program prevent it?

Small fluctuations around one set point switch the output on and off repeatedly. A program can use two set points a little apart, so the output changes only when clearly needed.

CCEA A-Level Technology and Design 8900

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Electronic Control SystemsOption A

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Microelectronic Control SystemsOption A

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Microelectronic Control Systems

Microcontroller systems, ADCs and DACs

3 things to know
A2 1

Overview

PICs as input, process and output, closed loop temperature control and hysteresis, feedback, anti-static handling, ADC step size and readings, DACs and sampling rate.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is a PIC?

Process

How does a PIC-based control system map onto input, process and output?

Key term

Compare a PIC with digital I/O only and one with mixed digital and analogue I/O.

Questions from this subtopic

Each one with the model answer underneath.

1
What is a PIC?
Model answer
A PIC, or peripheral interface controller, is a microcontroller: a small computer on a single chip. A PIC holds a processor, program memory, data memory and input/output pins.
2
How does a PIC-based control system map onto input, process and output?
Model answer
Sensors and switches connect to the PIC's input pins. The program is the process, and the output pins drive devices through interface circuits.
3
Compare a PIC with digital I/O only and one with mixed digital and analogue I/O.
Model answer
A digital-only PIC reads just logic 0 or 1 on each input pin. A mixed I/O PIC also has analogue inputs feeding a built-in ADC, so it can read sensor voltages directly.
4
Name a commonly used PIC with digital I/O only and one with analogue inputs.
Model answer
The PIC16F84A has digital input and output pins only. The PIC16F88 adds analogue inputs through a built-in 10-bit ADC.
5
Explain how a PIC can provide closed loop temperature control.
Model answer
A thermistor divider feeds an analogue input, and the program compares the reading with a set value. The PIC switches the heater on below the set value and off above it.
6
Why does on/off control with a single set point cause rapid switching, and how can a program prevent it?
Model answer
Small fluctuations around one set point switch the output on and off repeatedly. A program can use two set points a little apart, so the output changes only when clearly needed.

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The output voltage is V.

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