Int. Journal of Applied Sciences and Engineering Research, Vol. 5, Issue 1, 2016
© 2016 by the authors – Licensee IJASER- Under Creative Commons License 3.0
Research article
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ISSN 2277 – 9442
Determination of the reliability of a locally made clap activated
switch by part count analysis
Ehiagwina Ojiemhende Frederick1, Adewunmi Olugbenga Titus2, Bamigboye Oladayo Oladele3, Seluwa
Oludare Emmanuel4
Department of Electrical Electronics Engineering School of Engineering Federal Polytechnic, Offa, Kwara
State, Nigeria
DOI: 10.6088/ijaser.05007
Abstract: In this research work, the reliability of a locally designed and constructed clap activated switch
was determined. The sound of clap is detected by a small condenser microphone. The microphone
transduces the sound wave to electrical waves which is further amplified by transistor connected in the
common emitter configuration. The amplified output from the transistor is then fed to the Bistable
Multivibrator circuit. The part count method which assumes typical operating conditions of part or
components complexity, ambient temperature, various electrical stresses, operation mode and environment
(called reference conditions) was used for the estimation of the reliability of the Clap Activation Switch. It
is observed that the reliability of the Clap Activated Switch constructed locally have an estimated reliability
that ranges between 0.99706 for the first year of operation to 0.94299 around the twentieth year of
operation. Further work can be done by evaluating the reliability of the device using part stress analysis;
this will enable the determination of the reliability under actual operating conditions to be carried out.
Keywords: Electrical stresses, part count analysis, reliability, switch.
1. Introduction
Developing countries of the world are mainly consumers or, at best, assemblers of electronic devices
designed by developed nations. There are needs to fast track development and industrialization by
encouraging research into designing, construction, testing and mass production of electronic devices in
developing countries and Nigeria in particular. The government has shown interest in advancing the
country technologically. The clap activated switch can be used to switch ON/OFF devices and they are
designed and usually constructed in developed countries and shipped to developing nations. In this research
work, a clap activated switch was locally design and construct; hence there is the need to evaluate the
reliability of the device. The amplified output from the Bistable Multivibrator is connected to the relay; the
contact is connected to the power line and hence turns ON/OFF any electrical devices connected all the
way through the relay.
1.1 Reliability analysis
In general, reliability designates the ability of a system to perform its assigned function, where past
experience helps to form advance estimates of future performance. Reliability is a measuring index for the
performance of engineering systems defined reliability as the probability that a device or system will
perform its prescribed function adequately for the period of time intended under specified operating
conditions (Akinsanmi O. , "Determination of the Comparative Reliability of a Nokia 1200 Mobile Phone
—————————————
*Corresponding author (e-mail: frederick.ehiagiwna@fedpoffaonline.edu.ng)
Received on January, 2016; Published on February, 2016
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Determination of the reliability of a locally made clap activated switch by part count analysis
Charger", 2009; Abdullahi, Muazu, & Jibril, 2007; Faruk, Ayeni, Abdulkareem, & Moses, 2012). Reliability
can be determined through the mathematical concept of probability by identifying the probability of
successful performance with the degree of reliability. If a device or system does not fail during the time of
service it is said to perform satisfactorily. On the other hand, some devices are expected to fail, be repaired
and then returned to service during their entire useful life. In this situation a more appropriate measure of
reliability is called availability of the device in question. Therefore, in this work the reliability of the design
is evaluated using exponential distribution model. The exponential distribution model is defined in
(Akinsanmi, Sha'aban, & Ayo, 2009; Arsenault, 1980). The exponential failure density function f (t) is
defined by (1):
f t   e t
(1)
The reliability function is defined by (Akinsanmi, Sha'aban, & Ayo, 2009) in the form of (2):
Rt   e t
(2)
The generic failure rate, G of each component that makes up the clap activated switch is obtained from the
Military Handbook (MIL-HBK-217 Notice 2) (MIL-HDBK-217, 1991), using parts count method of
reliability prediction. In this paper, it is assumed that the failure of any components that makes up an
electronic system will result to system failure based on series theorem of reliability.
(Jones & Hayes, 1999) predicted the reliability of several selected Circuit Board of different types using
techniques such as HRD4, Siemens (SN29500), CNET, MIL-HDBK-217E and Bellcore (TR –TSY-00032)
models. Part count analysis were performed on the Circuit Board using Published failure rates and the
results was compared with observed field performance. It further noted system sensitivity to widely
differing parameter such as electrical stress, temperature and other   factors . While a framework and
procedure for predicting the reliability of electronic equipment at all levels was presented in (IEEE STD,
2003). On the other hand, (Goel & Graves, 2006; Bhargava, Banga, & Singh, 2014) summarized researches
in field of electronic system reliability. It reviewed the merits and demerits of traditional reliability
prediction models. It pointed out MIL-HDBK-217 as first and widely used predictive models, even as (Jais,
Werner, & Das, 2013) highlighted its shortcomings. However, the justification of it use in this research lies
in its simplicity and wide acceptability.
1.2 Part count method
This is one of the methods used in assessing the reliability of electronic devices. The part count method
assumes typical operating conditions of part or components complexity, ambient temperature, various
electrical stresses, operation mode and environment (called reference conditions). The failure rate for a part
under the reference conditions is calculated by using (3) (MIL-HDBK-217, 1991):
n
b,i   r i
(3)
i 1
where:
 r = the failure rate under the reference conditions.
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Determination of the reliability of a locally made clap activated switch by part count analysis
i  the number of components or parts.
It is convenient to specify the reliability of electronic equipment by some probability parameters, which
give indication of the failure rate of such a system or equipment, and does not depend on the operating time.
By using such parameters, it is also possible to compare the performance between different systems with
different operating periods. Two of such parameters that are commonly used are the mean time before
failure (MTBF) and mean time to failure (MTTF).
1.3 Mean time before failure (MTBF)
Systems users are usually concerned with the length of time that a system will run without failure. This is a
measure of the reliability of such system. For a repairable system, the time before failure is the critical
measure, while for non-repairable systems; the time distribution is exponentially decreasing and the mean
time before successful failure of the system. The MTBF can be obtained by running a system for
predetermined length of time under specified conditions. Calculating the average length of time before
failures could be seen as exponentially decreasing function and MTBF is the mean time before consecutive
failures. Hence for the failure rate  (is the number of failures per unit time), MTBF is given as
(Akinsanmi O. , "Determination of the Comparative Reliability of a Nokia 1200 Mobile Phone Charger",
2009), (Abdullahi, Muazu, & Jibril, 2007):
MTBF 
1

(4)
The reliability of the system ( R ) for a specified period ( t ) of failure free operation is as shown in (2).
1.4 Mean time to failure (MTTF)
The mean time to failure MTTF is used for components or items that are not repairable e.g. filament bulbs,
resistors, capacitors and so on, which are disposed as soon as they fail. This MTTF can be obtained by
stressing a large number of components under known conditions for a period of time and noting the number
of failures can obtain the MTTF (Taylor, 1989).
1.5 Equipment Failure Profile
Over the years, complex equipment and components have been found to follow a familiar pattern of failure,
which has been well documented. Hazard or failure rates have been calculated for equal time interval from
installation to replacement. When the failure rate is plotted against a time scale spanning the equipment life
time, the resulting graphics, popularly known as ``BATHTUB’’ is obtained as shown in Figure 2. It exhibits
three distinct periods or zones- the infant mortality period, the constant failure rate period and the wear out
period. Failure rate is usually expressed in failure per hour (or failure per thousand or even per million
hours) (Andrew, Jordan, & Lawrence, 1995).
1.6 Infant mortality period
This is the running-in period. During this period, the failure rate has been found to be high, due to other
design or manufacturing errors, misuse or misapplication of other identifiable causes. It however, falls off
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Determination of the reliability of a locally made clap activated switch by part count analysis
rapidly with operation. Failures in this period can be avoided during product development through the use
of stimulated tests, or by vigorous stressing during commissioning tests.
Figure 1: Equipment failure profile (Akinsanmi O. , "Reliability Assessment of UPS Systems in
Developing Countries", 2003)
1.7 Constant failure rate period
This period follows the running-in period. During this period, the failure rate is lowest and is a function of
the basic design. Failure results either through accidents or poor operation or maintenance and they can be
reduced by good control of operating and maintenance procedures. In this phase, the mean time to failure
(MTTF) is the reciprocal of the (constant) failure rate.
1.8 Wear out Period
This period manifests towards the tail end of the equipment component life. During this period, failure is
due to old age; various components are worn out, metals become embrittled, insulation dries out and so on.
Failure rates can only be reduced by preventive replacement of these components. Generally in some
systems, one or two of the phases (usually the early failures and wear out failures) could be more reduced
or effectively absent. Therefore, estimates for the parameters that affect the equipment failure profile of the
constituent components, especially the length of the constant failure rate period and the associated failure
rates are essential ingredients for predicting the reliability (Akinsanmi O. , "Reliability Assessment of UPS
Systems in Developing Countries", 2003)
1.9 Equipment availability
Equipment availability is the probability that an equipment will perform its required function at a stated
instant of time or over a stated period. Availability is a function of the utilization factor (U). The utilization
factor of a unit or system is op defined as the ratio of the operating time ( t op ) to the sum of the
maintenance time ( t m ) and idle time ( t id ) which may occur between completion of maintenance and use
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Determination of the reliability of a locally made clap activated switch by part count analysis
due to administrative reasons, and the operating time. Mathematically, the utilization factor U, was given
by (Akinsanmi O. , "Determination of the Comparative Reliability of a Nokia 1200 Mobile Phone Charger",
2009; Abdullahi, Muazu, & Jibril, 2007; Oroge, 1991) as expressed in (5).
U
t op
t id  t m  t op
(5)
If t id  0 , t m  0 , then U will approach its maximum value and can now be called availability of a unit
or system.
Mathematically, this can be expressed as shown in (6):
U max 
t op
t m  t opmin 
 At 
(6)
However, MTBF  top min  and MTTF  top
Where MTBF and MTTF is mean time before failure and mean time to failure respectively.
Then, the availability is as shown in (7):
At  
MTBF
MTBF  MTTF
(7)
And if the availability of equipment is stated as 0.99, it means that the equipment is working satisfactorily
for 99% of the time, and under repair for the remaining 1% of the time.
2. Materials and method
2.1 Principle of operation of the clap activated switch
The sound of clap is detected by the small condenser microphone that is shown in Figure 2 biased by
resistor R1 in the circuit. The microphone transduces the sound wave to electrical waves which is further
amplified by transistor Q1 connected in the common emitter configuration. The amplified output from the
collector of Q1 is then fed to the Bistable Multivibrator circuit also known as flip-flop. The flip-flop circuit
is made by using two transistors Q2 and Q3 .
In the flip-flop circuit, only one transistor conducts at a time and the other transistor is cut-off, and when it
receives pulse from external source then Q1 is cut-off and Q2 conducts. Thus the output from the
flip-flop is either at logic 0 or 1, and it remains in one state 0 or 1 until it receive trigger pulse from external
source. The sound energy from the clap which is the trigger for the flip-flop makes changes to the output.
The output from the flip-flop is of low current and is unable to drive the relay directly, hence, the output
need to be amplified by transistor Q4 . Transistor Q4 is connected to the relay (electromagnetic switch)
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Determination of the reliability of a locally made clap activated switch by part count analysis
which works as a mechanical switch. The relay contact is connected to the power line and hence turns
ON/OFF any electrical devices connected all the way through the relay (Horowity & Hill, 1989; Ojeleke &
Olawale, 2014).
2.2 System description
Figure 2: Circuit diagram of the Clap Activated switch (Ojeleke & Olawale, 2014)
The clap activated switch of Fig. 1 is made up of one step-down transformer T1 rated 240/12V, with a
secondary current of 300mA. The transformer steps down the supplied voltage to 12V a.c., half wave
rectification was employed using a single diode D1 and the output is connected to a capacitor C1 rated
1000 F / 16V for filtering purpose in order to have a smoothened DC voltage supply. The condenser
microphone is connected with resistors [ R1  R3 ] in series as a potential divider, which is then connected
to transistor Q1 (BC548) whose current is limited by R4 the output from Q1 is connected to Bistable
Multivibrator comprising of transistors Q2 and Q3 , resistors [ R5  R12 ], diodes D2 and D3 , and
capacitors C 3 and C 4 . The weak output from the Bistable Multivibrator is amplified by transistor Q4 biased
by R13 . Diode D4 prevents current from flowing back to the Bistable Multivibrator. The output from Q4 is
designed to control relay K 1 which performs the switching operation when a clap is made.
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Determination of the reliability of a locally made clap activated switch by part count analysis
3. Reliability assessment of electronic equipment
The expression for the parts count method of assessing reliability of the clap activated switch is given in (8)
as:
n
CAS   i  nR R  nC C  nQ Q  nT T  nD D  nK K  nCON CON  nMIC MIC (8)
i 1
where:
n R  Number of resistors in the clap activated switch
nC  Number of capacitors in the clap activated switch
nQ  Number of transistors in the clap activated switch
nT  Number of transformers in the clap activated switch
n D  Number of diodes in the clap activated switch
n K  Number of keys or relay in the clap activated switch
nCON  Number of connectors in the clap activated switch
nMIC  Number of microphones in the clap activated switch
 R  Failure rate of the resistors
C  Failure rate of the capacitors
Q  Failure rate of the transistors
T  Failure rate of the transformers
 D  Failure rate of the diodes
 K  Failure rate of the keys or relay
CON  Failure rate of the connectors
MIC  Failure rate of the microphones
CAS  Failure rate of the clap activated switch
By substituting (8) in (2), the reliability of the clap activated switch is given as (9):
RCAS t   e tCAS (9)
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Determination of the reliability of a locally made clap activated switch by part count analysis
4. Results and discussion
The design criteria presented above will be used to assess the locally constructed clap activated switch. We
can now obtain the failure rate. The conclusions arrived at will be used to assess the reliability, RCAS t  of
the clap activated switch, with the generic failure rate which has taken care of the environmental factors,
and the results of the failure rates are as shown in Table 1 below.
From the Table 1 the total failure rate is obtained to be 0.33503  10
6
Table 1: Failure rate of the component parts of the clap activated switch
Components of the
clap activated switch
(a)
Quantity ( ni )
(b)
Failure rate of the
generic part
Failure Rate of
the components
10 
10 
(c)
(d) = (b) *(c)
6
6
Resistors
16
0.00370
0.05920
Mica capacitors
7
0.00057
0.00399
MOSFET
1
0.01200
0.01200
Electrolytic
1
0.01300
0.01300
Diodes
5
0.00345
0.01725
Transistors
1
0.00015
0.00015
Transformer
4
0.00061
0.00244
Relay
1
0.04900
0.04900
Connectors
60
0.00130
0.07800
Switch
1
0.10000
0.10000
Total failure rate (CAS )
  d   0.33503
Reliability of the clap activated switch plotted against time can be obtained for the period of twenty (20)
years as shown in Figure 3, which indicates that the reliability of the clap activated switch decreases with
age. A reliability value of not less than 0.98 is expected for the first six (6) year of operation.
5. Conclusion
It is observed that the reliability of the Clap Activated Switch constructed locally have an estimated
reliability that ranges between 0.99706 for the first year of operation to 0.94299 around the twentieth year
of operation. Further work can be done by evaluating the reliability of the device using part stress analysis;
this will enable the determination of the reliability under actual operating conditions to be carried out.
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Determination of the reliability of a locally made clap activated switch by part count analysis
Figure 3: Estimated Reliability of the locally constructed clap activated switch
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