Project
by Robert Reed
Building a Pulse Generator
Design, Troubleshoot, and Calibrate Electronic Circuits
If you work with digital and logic circuits (and we all
do), you will find this instrument handy for design,
troubleshooting, and calibration of electronic circuits. Although I own a somewhat expensive commercial function generator, I find that this pulse generator is
the one I reach for most of the time. The generator is
fairly easy to build and uses a straightforward design.
It requires six integrated circuits and two transistors.
In addition, you will need a power supply of 15 volts at
200 mA.
You may build this unit as shown or add/delete stages
if you prefer something more customized for your needs.
In two years of use, I have not felt any need to change the
design, as it has worked well under all situations.
I housed this unit in a 7 x 4 x 5-inch box. If you build
it exactly as shown, do not use a box any smaller than
this, as you will be crowding the front panel controls.
Before we get into the construction, I feel that a description of the theory of operation is in order.
Referring to the schematic (Figure 1), the heart of the
unit is the U4 rate generator and the U3B width generator.
The U4 multivibrator rate is set in six steps by capacitor
selection of S6a, S6b.
This, in turn, is varied by potentiometer P2 to give
complete coverage between bands. The RATE change
is two microseconds to one second continuous with R9
and P2 values giving an approximate 10 percent overlap between ranges. The squarewave output is sent
through U5a,b (AND gate), which provides buffering to
U4. One gate sends the signal to J3 (internal trigger
out). The other gate sends the signal to U2b-P5, which
isolates the various inputs from each other by an OR
gate function.
The positive edge from the output of U2b triggers
the width generator, U3b. Incidentally, all of these circuits are positive-edge triggered. U3b is a monostable
multivibrator, and its output width is determined by
capacitor selection via S7a, S7b. As in U4, it is varied by
Figure 1. The heart of the unit is the U4 rate generator and the U3B width generator.
F
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NUTS & VOLTS
E
v
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t
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i
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g
+ 15 V C1 + 15 V
.05
EXT. TRIG.
4 R5 2.2K
+
J1 12
R1 10K U1A
5-
R2 1.2K R3 15K
+ 15 V
INT. TRIG. OUT
J3
+ 15 V
10
-
EXT. GATE U1B 7
9+
J2 R4 10K D2 R6
2.2K
3, 6, 8
+ 15 V
11
U5A
13 12
+ 15 V
0.1
1
3
U5C
2
C16
0.22
+ 15 V RUN
S2
8
9
2 U2A
1
+ 15 V
8, 9, 12
13, 14
1,2
STOP
7
U4
D3
3, 5, 6
R9
9.1K
8
10
4 U5B
9
S6A
3
6
5 U2B
4
C4 R10
.05 22K
16, 3
6
4 U3B 7
1, 8 2 5
S7B
S7A
Q2
12
U2C
11
12
Q1
R16
470
+ 15 V
C11-C15
*SEE TEX T
R11
5.1K
RATE
100K
P2
5
4
U5D
6
+ 15 V
R7
22K
C2
.05
S6B
+ 15 V
SINGLE
S3
C17
1.0
DC AC
R17
1 K
P4
LEVEL
1 K
J4
13
U3A
12 10
15 14 9 11
S1
BURST C3 R8
.05 5, 1K
BURST LENGTH
1.0 M
P1
+ 15 V
C5-C10
*SEE TEXT
WIDTH
50K
P3
R12 + 15 V 22K R13
22K
R14
1.8 K
MAIN OUT
+ 15 V
POWER
0.1 A S8
120V/15V
120VAC
C19
1000 NF
-+
+
V IN V OU T
U7 7815
GRD
+ C20
100 MF
+15V
10 5
11 U6 6
R15 1, 3 7 9, 13
680 14
C18
.05
+5V
J5
T TL OUT
R18
22K
V IN V OU T
U8 7805
GRD
+5V
Pilot
46
APRIL 2005
