This a project for the ECET 270 class at Purdue College of Technology New Albany. It was completed and presented at the close of the Spring 2014 Semester.

1. Variable Pressure Detector
ECET 270
Andy Schnobrich

2. 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.

3. The Wien-Bridge Oscillator
+15V
15V
741
2
3
7
4
6
500
4.7k
RB
10k
R2
12.1k
R1
12.1k
C2
.0022FC1
.0022F
RA
VOUT

4. The Peak Detector and Voltage Comparator
Circuit
+15V
15V
741
2
3
7
4
6
Vin
(13.90°)V
@5.86kHz
D1
1N914
C1
.47F
R1
10k
IDC
+15V
15V
741
2
3
7
4
6
R1
150k
R2
150k R3
680
VLED
VCC
ILED
V3
V1

5. The RC Wheatstone Bridge and The
Instrumentation Amplifier
+15V
15V
741
2
3
7
4
6
C1
70pF
R1
56k
R2
100k
C2
60.5pF
FROM THE WEIN BRIDGE
OSCILLATOR
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
12.1k
R2
12.1k
R2
12.1k
R2
12.1k

6. 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
0.0033F
C2
0.0033F
R2
12.1k
R3
12.1k
TATION
ER
VOUT
330
RB
0
2
4
6
8
10
12
14
16
18
250 2250 4250 6250 8250 10250
Vout_pp(V)
frequency (Hz)
Frequency Response

7. The Active Rectifier Circuit
+15V
15V
741
2
3
7
4
6
+15V
15V
741
2
3
7
4
6D1
1N914
D2
1N914
R2
12.1k
R1
12.1k
R3
12.1k
R5
12k
+15V
15V
741
2
3
7
4
6
VOUT
VIN
R4
10k

8. 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

9. 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
22F
VOUT5
VOUT1
R4
680
2N3903
RC1
1k
5V
C1
22F
VOUT4
VOUT3
R6
680
2N3903
RC3
1k
5V
C3
22F
VOUT6
FROM ACTIVE
PEAK DETECTOR
RB2
22k
RB1
22k
RB3
1k
Normal
1st Level
2nd Level
3rd Level
0V
0V
0V
0V
FROM ACTIVE
PEAK DETECTOR
VOUT1
VOUT2
VOUT3
-13V
-13V
-13V
+13V
+13V
+13V
0VVOUT6
0VVOUT5
0VVOUT4
+5V
+5V
+5V

10. 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
0.1F
RT
150k
VOUT7
1
3
2
4 8
7
6
5
RB
1M
RA
100k
C1
0.068FC2
0.01FOUTPUT
+5V
LM555

11. The Counter, Decoder, and Display Circuits
74190
FROM 555 TIMER
FROM 1/3 PRESSURE
TRANSISTOR SWITCH
FROM MONOSTABLE
MULTIVIBRATOR
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

12. 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's
220
.
.
.
.
R's
220
a
b
c
d
e
f
20
10
7
8
9
19
18
17
16
vcc
.
.
.
.
PLD
FULL
2/3
1/3
FROM TRANSISTOR
DRIVERS
MSB LSB