Cellphone-Based Remote Controller for Water Pump

nconvenience in switching on a water pump installed in a remote farm is a common problem faced by farmers. Many circuits have been developed to solve this problem. Most of them are expensive and microcontroller-based. Here we present a cellphone-based remote controller for water pump. By calling the cellphone attached to the controller, the water pump can be directly activated.

Circuit and working
Fig. 1 shows the block diagram of cellphone-based remote controller for water pump. Fig. 2 shows the circuit. The circuit is built around DTMF decoder IC MT8870 (IC1), timer NE555 (IC2) wired as monostable multivibrator and a few discrete components. The main component of the circuit is IC MT8870. This DTMF decoder has band-split filter and digital decoder functions. It offers the advantages of small size, low power consumption and high performance.

Fig. 1: Block diagram of cellphone-based remote controller for water pump 

 Fig. 2: Circuit of cellphone-based remote controller for water pump 
Once monostable timer IC2 is triggered, its output goes high for the preset time period. The time period depends on the values of resistor R7 and capacitor C4. It can be adjusted between 8 and 50 minutes using pot-meter VR1. The high output at pin 3 of IC2 energises relay RL1 to switch on the water pump.

The triggering pulse for IC2 is generated by DTMF decoder IC1 and the arrangement of diodes D1 through D5. Std pin of IC1 provides a high pulse when a valid tone-pair is received. Transistor T1 conducts only when outputs Q0 through Q2 and Std are high simultaneously. This can be achieved by sending digit ‘7’ through DTMF.

The water pump controller is connected to a dedicated cellphone through connector J1 with auto-answering mode enabled. The DTMF signal sent from the user end is decoded by the DTMF decoder and the corresponding binary-coded decimal (BCD) value appears on outputs Q0 through Q3. In this circuit only three of them are used.

Working of the circuit is simple. To switch ‘on’ the water pump, call the cellphone connected to the controller circuit and press ‘7’ once the ring stops. LED1 will glow to indicate that the water pump is switched on. The water pump turns off automatically after the preset time. LED1 turns off simultaneously.

Construction and testing
An actual-size, single-side PCB for cell-phone-based remote controller is shown in Fig. 3 and its component layout in Fig. 4. Suitable connector is provided on the PCB to connect the cellphone. Assemble the circuit on a PCB to minimise time and assembly errors. Carefully assemble the components and double-check for any overlooked error. Use suitable IC socket for MT887 and NE555 ICs.

Fig. 3: An actual-size, single-side PCB for cellphone-based remote controller

Fig. 4: Component layout for the PCB

Use relay RL1 with contact current rating capable of carrying the water pump’s current.

To test the circuit for proper functioning, press switch S1 and verify 5V at TP1 with respect to TP0. Connect the cellphone to the controller using connector J1. Call this cellphone and press ‘7’ once the ring stops. At the same time, verify high-to-low triggering pulse at TP2. TP3 now should be high for the preset time period.

 

Remote Control for Home Appliances

Using this circuit, you can remotely control the switch-on and switch-off operation of your AC mains operated home appliances. The working range of the circuit depends on the orientation and the intensity of the IR beam.

The circuit consists of a transmitter and a receiver.

 Fig. 1: Transmitter circuit
Fig. 1 shows the transmitter circuit. It is built around timer IC NE555 wired as an astable multivibrator. The multivibrator produces a pulsed output waveform with ‘on’ time of about 57 µs and ‘off’ time of about 326 µs, which means it generates about 2.6 kHz. The output of IC1 is fed to IR LED1 through current-limiting resistor R3. The IR LED1 used here is the same as in TV remotes. The circuit operates off a 9V battery, which is connected to the circuit through switch S1.

Fig. 2 shows the receiver circuit. It consists of phototransistor L14F1 (T1), voltage regulator 7805 (IC2), three 2N2222 transistors (T2, T3 and T4), dual voltage converter LM319 (IC3), dual J-K flip-flop 74109 (IC4) and some discrete components. The circuit operates off a 9V battery, which can be connected to the circuit through switch S2.

The Darlington pair built around transistors T2 and T3 amplifies the photo-current generated by the photo-transistor (T1). The equivalent photo-voltage appears across resistor R4. So across resistor R4 you get a replica (in term of wave shape but not in amplipude) of what you produce at the output of IC1 in the transmitter. The amplitude would vary with distance and other factors such as the angle of arrival of the IR beam at sensor L14F1.

 Fig. 2: Receiver circuit



The low-pass filter constituted by resistor R7 and capacitor C4 produces about 3V DC. This DC voltage is fed to the junction of the inverting input of N1 and the non-inverting input of N2. The window comparator (IC3) is designed such that whenever the input voltage is between 2 and 4 volts (greater than 2V but less than 4V), its output goes high. If the input voltage is less than or equal to 2V, or more than or equal to 4V, the output goes low.

The window output is fed to the clock input of J-K flip-flop CD74109 (IC4). IC4 is wired in toggle mode. That means its output goes high if it is initially low and vice versa every time it is clocked. The output of IC4 is fed to the base of relay-driver transistor T5. Relay RL1 energises to light up the bulb when transistor T5 conducts.

Working of the circuit is simple. Initially, when no IR beam is falling on sensor photo-transistor T1, the DC voltage appearing at the input of the window comparator is nearly zero. The window output remains low. Transistor T5 is cut-off and the relay remains de-energised.

When switch S1 is pressed momentarily, the IR beam falls on the photo-transistor for this short period of time and a postive-going pulse appears at the input of the window comparator. The output of the comparator goes low, which toggles the flip-flop (IC4) and transitor T5 conducts. Relay RL1 energises to switch on bulb B1.

Assemble both the circuits on separate PCBs and house in suitable cabinets. In the transmitter unit, fix IR LED1 on the front side and switch S1 on the back side of the cabinet. Keep the 9V battery inside the cabinet.

Similarly, in the receiver unit, fix the photo-transistor (L14F) on the rear side such that the IR beam falls on it. To avoid circuit malfunction, cover the phototransistor (T1) with a suitable contraption so that the phototransistor is not exposed to unwanted light sources. Fix switch S2 on the front panel and the relay on the back side. Keep the 9V battery inside the cabinet.