2.6 Timer
A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. It works reverse in direction compared to the stopwatch. Whereas a
stopwatch counts upwards from zero for measuring elapsed time, a timer counts down from a specified time interval, like an hourglass. Timers can be mechanical, electromechanical,
electronic quartz, or even software as most computers include digital timers of one kind or another. In this project, the mechanical or electronic timer probably uses to complete
this circuit. The timer has a control relay or contactor build in it. Control relay or contactor is an electromechanical device which activates one or more switches according to the
current through a coil not connected to the switches. A relay is essentially an electromagnet with two possible states arranged so that when there is sufficient current the core of the
relays coil attracts a ferromagnetic armature which mechanically operates switches; a spring holds the armature away from the core when not actuated. The spring is designed to
snap the contacts between two stable mechanical states; there should not be a range of coil current which allows the contacts to be in an intermediate state.
2.7 Inverter
In this project, a 12V rechargeable battery will be used to store the energy which supplies the voltage to the rain sensor and timer. So, the power supply needs to be
converted from 12V dc to 240Vac because the rating of water pump is 240Vac. The solution is an inverter will be installed to convert the supply. The inverter will converts
direct current DC to alternating current AC; the resulting AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control
circuits. Figure 2.5 below show the inverter circuit that might be used in completing this project. In this circuit, the DC supply will converted to the AC supply forms then boost up
to the 240Vac.
Figure 2.5: An Inverter Circuit
2.8 Water Pump
In this project, a 240Vac water pump will be used to flow the water in completing the irrigation process. There are several types of water pump available in market depend on
the requirement of the user. For this project, only common water pump needed that can supply water from a tank to the crops or plant next to the pump. So, the decision is to use
the water pump that being commonly use in aquarium fish tank to circulate the water. The cost will be cheap and easy to get in market. Figure 2.6 shows the sample of water pump at
the local market.
Figure 2.6: A Common 240Vac Water Pump
2.9 First Review: Study on Portable Power Supply Equipment Using The Flexible
Solar Cell Sheet By Sonoda Toshiaki, Iguchi Yoshio, Yonemochi Shigenobu, 1995- 1997 [11]
The article describes about study on portable power supply equipment which carried out in 1995-1997. This study aim at obtaining the technical data for realizing
portable power supply equipment using the solar cell as a source of energy which is used as a power supply for the field and which is excellent in maintenance, supply, and secrecy,
and does not have noise, and exhaust gas and exhaust heat.
The equipment consists of the amorphous silicon solar cell module covered by the surface protection film processed with the sand mat, the lithium ion secondary battery, and
the charger. The result of this study is as follows:
a The solar cell module were the unfolding condition size
900mm600mm1.5mm, the folding condition size 180mm300mm20mm, the weight of 440g, the maximum output of 22W, the surface reflectance of
maximum of 2, and the conversion efficiency of 5.8.
b The secondary battery and the charger were able to be charged even if the
output of the solar cell module changed 14V-20V.
2.10 Second Review: Solar Electricity in Rural Villages By S.N. Singh, A.K. Singh,
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