William Sandqvist william@kth.se Comparator an 1 bit AD-converter A - - PowerPoint PPT Presentation

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William Sandqvist william@kth.se Comparator an 1 bit AD-converter A - - PowerPoint PPT Presentation

Sep 10, 2022 438 likes •791 views

William Sandqvist william@kth.se Comparator an 1 bit AD-converter A comparator is a sensitive amplifier for the difference between input voltages. The slightest positive difference means that the output get (1) or negative difference get (0).

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William Sandqvist william@kth.se

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William Sandqvist william@kth.se

Comparator an 1 bit AD-converter

A comparator is a sensitive amplifier for the difference between input voltages. The slightest positive difference means that the

  • utput get (1) or negative difference get (0).

The comparator can be used to accurately determine when a voltage UIN pass a certain reference voltage UREF.

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William Sandqvist william@kth.se

PIC-processor comparators

PIC16F690 has two internal analog comparators. They can be connected to different pins or to internal units. The comparator is a very versatile component..

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Many configuration options!

William Sandqvist william@kth.se

C1:s and C2:s outputs are are accessible internally, but can also be connected to external pins ( eg. C2OUT → RC4 ).

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Analog function?

William Sandqvist william@kth.se

One choose to use the "analog" function on pins with the ANSEL registers. PIC16F690: Default-setting is the analog function – so in practice choose to remove analogous function when you need digital.

RA0 RA1 RA2 RA4 RC0 RC1 RC2 RC3 RC6 RC7 RB4 RB5

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CMP2 at lab

William Sandqvist william@kth.se

ANSEL.4=1; ANSEL.6=1; TRISC.0=1; TRISC.2=1; TRISC.4=0;

RA2/C1OUT

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Control registers

William Sandqvist william@kth.se

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CMP2 at lab

William Sandqvist william@kth.se

1 C2CH.0=0; C2CH.1=1; C2R=0; C2POL=0; C2OE=1; C2ON=1;

  • 1
  • 1

1

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CMP2 at lab

William Sandqvist william@kth.se

C2CH.0=0; // C12IN2- C2CH.1=1; // C12IN2- C2R=0; // C2IN+ C2POL=0; // not invert SR1=0; // no SR-latch C2OE=1; // out to pin C2ON=1; // C2 on ANSEL.4=1; // analog ANSEL.6=1; // analog TRISC.0=1; // RC0 input TRISC.2=1; // RC2 input TRISC.4=0; // RC4 output

With these settings we use Comparator 2 as independent stand alone component!

In gray – default setting

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William Sandqvist william@kth.se

Lab: try a Comparator

When the voltage at the twerminal on the 10k potentiometer is passing reference voltage 2.5V (5V divided by two) the comparator output turns on. The trip point is very distinct.

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William Sandqvist william@kth.se

Lab: try a Schmitt-trigger

A third 1k resistor from the output to the "+" input shifts the reference level so that we must now turn more to change the output. There are dual threshold for on and

  • ff. The function will be more secure. The connection is

called the Schmitt trigger and the phenomen of dual tresholds is called hysteresis.

Hysteres.

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William Sandqvist william@kth.se

Otto Schmitt

A schmitt-trigger has ”snap action”. When you have passed the trip-point the process is no longer possible to prevent …

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William Sandqvist william@kth.se

Threshold voltages? (10.10)

0V 5V ? ?

3 1 5 5 , 1 5 , 5 = +

? 0V 5V

3 2 5 5 , 1 1 5 = +

?

Voltage division Voltage division

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William Sandqvist william@kth.se

RC-oscillator

The comparator charges the capacitor to the upper trig level, then turn the output on and discharges the capacitor to the lower trigger

  • level. The frequency of the output of the comparator depends on the

product R·C. As C is constant R will determine the frequency.

3 2 3 1

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William Sandqvist william@kth.se

Lab: try RC-oscillator

Schmitt trigger is continuously charging and discharging the capacitor voltage between the two threshold levels. Along with the earphone, we now have a buzzer!

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William Sandqvist william@kth.se

Sensors

NTC-Thermistor LDR-Photo resistor

Try some resistive sensors … We will measure frequency with the PIC-processorn CCP- unit later in the course …

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Sensors

FSR-Force Sensitive Resistor, press between your fingers.

William Sandqvist william@kth.se

Try some resistive sensors …

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Simulate the RC-oscillator

William Sandqvist william@kth.se

”sensor”

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Simulate RC-oscillator

William Sandqvist william@kth.se

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William Sandqvist william@kth.se

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A more stable RC-oscillator

William Sandqvist william@kth.se

About 2 130 000 results (0,30 sekonds) Hans Cam enzind designer of the 555 timer (1934-2002) Signetics 1970

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555 as RC-oscillator

William Sandqvist william@kth.se

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555 RC-oscillator

William Sandqvist william@kth.se

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The 555 inside story

William Sandqvist william@kth.se

5kΩ 5kΩ 5kΩ

Two comparators and one SR-latch.

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555 as Schmitt-trigger

William Sandqvist william@kth.se

With these connections the 555 becomes a Schmitt-trigger with the threshold levels 1/3 and 2/3 of the supply voltage.

3 2 3 1

This circuit has better "performance" than the single comparator connected as Schmitt trigger we have shown previously.

IN

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William Sandqvist william@kth.se

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PIC-processor SR-latch

William Sandqvist william@kth.se

Programable, self resetting, bits to generate pulses on S and R. SR-latch output can be read by the program (C1OUT, C2OUT),

  • r connected directly to the chip pins (C1OUT/RA2, C2OUT/RC4).
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PIC-processorns SR-latch

William Sandqvist william@kth.se

”1” ”1”

SR-latchs inputs can be configured to connect to the comparators.

C1OUT C2OUT

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William Sandqvist william@kth.se

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PIC-processor as oscillator

William Sandqvist william@kth.se

PIC-processor two comparators and SR-latch can be configured as a RC-

  • scillator, ”555 style”

A stable oscillator is needed when it is C that the sensor is – as the capacitive sensing.

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Touch-control

William Sandqvist william@kth.se

Vandal proof button at the pedestrian crossing!

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Touch-control

William Sandqvist william@kth.se

Moore contacts – Keyboard. Comparators inputs are multiplexed to the same pins – useful when you want to sense several keys …

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Touch-control

William Sandqvist william@kth.se

ch1 ch2 ch3 ch4

ch1+ch2 ch2+ch4 ch3+ch2 ch1+ch3

ch3+ch4 ch1+ch4

Moore contacts – Keyboard.

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William Sandqvist william@kth.se