Many of us face problem when we out of our home like if we want to on the motor, so that when we reach home water will be filled in over head tank or we want to on other appliances like light fan etc.
Hence to solve this problem we have describe a simple circuit which will on your device or appliances remotely and it will become off automatically after preset time interval.
Many circuits have been developed so far to solve this problem but main advantage of this circuit is uses readily available components and this circuit is not expensive as well because this circuit is made using without microcontroller.
Fig. 1: Prototype of Remote Control for Devices using Cell Phone Circuit on Breadboard
This circuit is based on two IC’s namely MT8870 which is DTMF decoder IC and another is NE555 timer which is wired as monostable multivibrator with few more components like crystal, relay, resistors and capacitors.
How to operate a device remotely
In this circuit for operating a device we will require two cell phone, one will be with us from which we will call on the other cell phone which is connected to device. And other cell phone will be connected to the device in auto answer mode. For operating the device call on the cell phone which is connected to the device as this cell phone is in auto answer mode it will pick up the call automatically . When ring stop dial number 7 from the keypad of the mobile from which you are calling. Now the device connected to it with the relay start operating and will become off automatically after certain time period.
Working of circuit
Connect the cell phone with the head phone or ear phone properly at mobile phone audio jack. Now when you call on the mobile connected with device at the receiving end DTMF decoder IC will provide a high pulse at pin 15 after detecting the valid tone pair. This will trigger the pin 2 of IC2 and its output will go from high to low. This in turn make the output pin 3 of IC2 high and the transistor T2 connected to it start conducting because of this relay energise and device become on. The time period for which device remain on can be adjusted with the help of variable resistor VR1 and capacitor C4. By increasing or decreasing the value of variable resistor and capacitor time period can be increased or decreased. This can be calculated by the below formula-
Time period = 1.1*VR1*C4 in seconds
In this circuit transistor T1 will only conduct when all the outputs pin 11, pin12, pin13 and pin15 will become high simultaneously with the help of diode D1 to D5. This can only be done by pressing the number 7 through DTMF decoder. The DTMF signal send from the dialler mobile end is decoded by the DTMF decoder and its respective BCD value appear at the output on pin 11, pin12, pin13. That’s why to on the device we are using number 7.