Lab of Experiment
One-Shot (Monostable)
Chia-Chun Tsai
What is One-Shot

Vout output a voltage for a time T each, if a
signal to trigger once to the input.
Input
Trigger
Chia-Chun Tsai
One-Shot
(Monostable)
Vout
2
1
555 Timer
VCC: 5V~15V
GND: 0V
OUT: 0V or VCC
RST(Reset): if RST=0V, OUT=0V
RST=Vcc if normal state
THR(Threshold): if TH≧2/3 VCC,
then via DIS (discharge) and
OUT=0V
TRI(Trigger): if TR≦1/3 Vcc, then
OUT=VCC
Con(Control voltage): Connect
0.1μF to GND
DIS(discharge) :
Chia-Chun Tsai
3
One-Shot based on 555
Vout: 0V-5V-0V Pulse
Vc1: 0V 2/3*5V0V
exponential wave
T = 1.1*R1*C1
= 1.1*5k*47μ
=258.5ms
Chia-Chun Tsai
4
2
555 One-Shot Applications
Chia-Chun Tsai
5
One-Shot to Turn on a Lamp
Chia-Chun Tsai
6
3
DC-6V Relay
Chia-Chun Tsai
7
555 One-Shot in Series
Chia-Chun Tsai
8
4
Traffic Signal based on 555 One-Shot
Chia-Chun Tsai
9
One-Shot based on 74121
A1
0
x
x
1
10
1
10
0
X
Chia-Chun Tsai
A2
x
0
x
1
1
10
B
1
1
0
x
1
1
Q
0
0
0
0
pulse
pulse
10
1
01
01
pulse
pulse
pulse
X
0
10
5
Two RC Choices for 74121
Q: 0V-5V-0V Pulse
T=0.693RC=0.693*5k*47μ
=162.855ms
R= 1.4kΩ~40kΩ
C=0~1000μF
Chia-Chun Tsai
Q: 0V-5V-0V Pulse
T=0.693(R+2kΩ)C
=0.693*(5k+2k)*47μ
=227.997ms
R= 1.4kΩ~40kΩ
C=0~1000μF
11
74121 One-Shot Applications
Q: 0V-5V-0V Pulse
T=0.693(R+2kΩ)C
=0.693*(33k+2k)*100μ
=2.4255s
R= 1.4kΩ~40kΩ
C=0~1000μF
Chia-Chun Tsai
12
6
74121 One-Shot in Series
Chia-Chun Tsai
13
7