CHAPTER 3 METHODOLOGY 3.1 Overview The Water Monitoring ...

Figure 3.7 show that a transistor driven relay circuit is used to connect betweenmicrocontroller and motor pump. Generally this relay will energize when supply voltage,V in is 5 volt (HIGH) and will OFF when V in is 0 volt (LOW).U25VU24240V AC (L)U27NU1U18D1D1N4001NCCOMNOA1 2MOTOR PUMPBP2.1R1Q1Relay_SPDT_b1kQ2N3904Figure 3.7: Pump Circuit with Transistor Driven RelayA relay will operate when a suitable ‘pull-in’ and ‘holding’ dc current is passthrough its energizing coil. An NPN transistor is using to control the coil current. A lowpowercircuitry is providing enough base current to turn the transistor on and off. An NPNtransistor will control the relay with a 5V coil, operating from a +5V supply. Series baseresistor R1 is used to set the base current for Q1, so that the transistor is driven intosaturation (fully turned on) when the relay is to be energized. A very little power willdissipate when the transistor has a minimal voltage drop. A power diode D1 (1N4001) isconnected across the relay coil, to protect the transistor from damage due to the back-EMFpulsed generated in the relay coil’s inductance when Q1 turns off.20