Variable Pressure Detector

Variable Pressure Detector ECET 270

Andy Schnobrich

Overview This project utilizes a variable

capacitor as a pressure switch. The analog portion of the circuit is used to detect how much the switch is depressed. The digital portion of the circuit is used to Display the time that the switch is depressed and to display the current pressure level.

The Wien-Bridge Oscillator

+15V

15V

741

2

3

7

4

6

500

4.7k

RB

10k

R2

12.1k R1

12.1k

C2

.0022FC1

.0022F

RA

VOUT

The Peak Detector and Voltage Comparator Circuit

+15V

15V

741

2

3

7

4

6

Vin

(13.90°)[email protected]

D1

1N914

C1

.47FR1

10k

IDC

+15V

15V

741

2

3

7

4

6

R1

150k

R2

150k R3

680

VLED

VCC

ILEDV3

V1

The RC Wheatstone Bridge and The Instrumentation Amplifier

+15V

15V

741

2

3

7

4

6

C1

70pF

R1

56kR2

100k

C2

60.5pF

FROM THE WEIN BRIDGEOSCILLATOR

VOUT2VOUT1

+15V

15V

741

2

3

7

4

6

+15V

15V

741

2

3

7

4

6

+15V

15V

741

2

3

7

4

6

R2

12.1k

R1

10k

VOUT1

VOUT2

Vy

Vx

VOUT1

VOUT2

VOUT

R2

12.1k

R2

12.1kR2

12.1k

R2

12.1k

R2

12.1k

The Second Order Active Band Pass Filter

+15V

15V

741

2

3

7

4

6

+15V

15V

741

2

3

7

4

6

R1

12.1k

RA

12k 33k

C1

0.0033F

C2

0.0033F

R2

12.1k

R3

12.1k

FROMINSTRUMENTATION

AMPLIFIER

VOUT

330

RB

250 2250 4250 6250 8250 1025002468

1012141618

Frequency Response

frequency (Hz)

Vout

_pp

(V)

The Active Rectifier Circuit

+15V

15V

741

2

3

7

4

6

+15V

15V

741

2

3

7

4

6D1

1N914

D2

1N914

R2

12.1kR1

12.1k

R3

12.1kR5

12k+15V

15V

741

2

3

7

4

6

VOUT

VIN

R4

10k

The Active Peak Detector and Voltage Comparator Circuits

+15V

15V

741

2

3

7

4

6

+15V

15V

741

2

3

7

4

6

+15V

15V

741

2

3

7

4

6

R3

100k

R2

100k

R1

100k

R6

680

R5

680

R4

680

LED3

RED

LED2

YELLOW

LED1

GREEN

VOUT1

VREF1

3.9V

15mA

VREF2

6.3V

VREF3

10.2V

VOUT2

VOUT3

VOUT4

15V

15V

15V

15mA

15mA

The Transistor Drivers, and Passive Low Pass Filters

R3

100k?

R2

100k?

R1

100k?

VREF1

VREF2

VREF3

VOUT2

15V

15V

15V

R5

680

2N3903

RC2

1k

5V

C2

22F

VOUT5

VOUT1

R4

680

2N3903

RC1

1k

5V

C1

22F

VOUT4

VOUT3

R6

680

2N3903

RC3

1k

5V

C3

22F

VOUT6

FROM ACTIVE PEAK DETECTOR

RB2

22k

RB1

22k

RB3

1k

Normal1st Level

2nd Level

3rd Level

0V

0V

0V

0V

FROM ACTIVEPEAK DETECTOR

VOUT1

VOUT2

VOUT3

-13V

-13V

-13V

+13V

+13V

+13V

0VVOUT6

0VVOUT5

0VVOUT4

+5V

+5V

+5V

The Monostable Multivibrator, and 555 Square Wave Oscilator Circuits

VOUT4

Q4: 2N3904

5V

SN74121

2

3

4

5

6

7

14

13

12

11

10

9

8

1

5V

NC NC

NC

NC

NC

NC

OUTPUT

RB4

6.8k

RC4

1k

Cext

0.1F

RT

150k

VOUT7

1

3

2

4 8

7

6

5

RB

1M

RA

100k

C1

0.068FC2

0.01FOUTPUT

+5V

LM555

The Counter, Decoder, and Display Circuits

74190

FROM 555 TIMER

FROM 1/3 PRESSURETRANSISTOR SWITCH

FROM MONOSTABLEMULTIVIBRATOR

74190

74190

7446

a

b

c

d

e

f

d

R1

220

R7

220

.

.

.

.

7446

a

b

c

d

e

f

d

R8

220

R14

220

.

.

.

.

7446

a

b

c

d

e

f

d

R16

220

R22

220

.

.

.

.

R15

220

RCO

RCO

CLK

CLK

1/10's place

1's place

10's place

The Pressure Display Circuit

7

1

2

6

7446

8

16

vcc

13

12

11

10

9

15

14

a

b

c

d

e

f

g

R's220

.

.

.

.

R's220

a

b

c

d

e

f

20

10

7

8

9

19

18

17

16

vcc

.

.

.

.PLD

FULL

2/3

1/3

FROM TRANSISTORDRIVERS

MSB LSB