There are several designs that the author has seen for controlling appliances remotely via a mobile phone, but they have all involved connecting a microcontroller to the serial port of the phone and either using the Caller ID, or parsing data from an SMS message. Not only are these devices complex to build, they are also specific to a particular model of phone.

Mobile Phone Switch – Freely phone home and control an appliance

THERE are several designs that the author has seen for controlling appliances remotely via a mobile phone, but they have all involved connecting a microcontroller to the serial port of the phone and either using the Caller ID, or parsing data from an SMS message. Not only are these devices complex to build, they are also specific to a particular model of phone.

The circuit prsented in Fig.1 is much easier and cheaper to build and should work on any mobile phone, as long as the screen lights up when it receives a call. The way it works is simple, the mobile phone receives a call causing its screen to light up, a lightdependent resistor (LDR) detects this and triggers a flip-flop (IC1) which turns a relay on or off, thus controlling the power to whatever is connected to the relay contacts.  Finally, as the circuit does not answer the call, nor receive an SMS message, there are no call charges incurred.

The circuit is based around a 4013 dual flip-flop IC, which is configured in such a way that its two outputs change state with each high-going pulse to its trigger input. LDR1, which is an ORP12 light dependent resistor, is placed so that it faces the screen of the
mobile phone. The sensitivity of LDR1 can be adjusted by VRl.

When the phone rings and the screen lights up, the resistance of LDR1 falls, this turns on transistor TR1, which could be any sort of general purpose NPN transistor. Capacitor C1 acts as a smoothing capacitor, which maintains a continuous high logic level even if the screen on the mobile phone flashes when it rings. If the screen of the phone you are using doesn’t flash then this component can be omitted.

Resistor R2 pulls the input to IC1 low and also discharges C1 when the phone is not ringing. Transistor TR2 is controlled by the Q1 output of IC1 and is used to turn on or off the relay, RLAl, which controls the Live mains supply of the attached device.

LEDs D1 and D2 indicate whether the relay is on or off and diode D3 protects the circuit from the back EMF pulse induced at the moment that the relay coil is turned off. Switch Sl can be used to manually trigger the circuit and can be omitted if not required.

The whole circuit, along with the phone, should be mounted in a lightproof enclosure so it is not accidentally triggered by ambient light. If the circuit is to be in permanent operation then you should ensure the phone’s charger is connected to prevent the battery running out.

It is a good idea to use a brand new sim card, which can usually be obtained for free, or very little cost, from most of the major mobile network providers. This will make the circuit more reliable as only you will have the telephone number to operate the device. However, the circuit will still be triggered by the occasional wrong number, or text message sent by the network provider, so it shouldn’t be used to control any critical appliances.

Article reproduced by permission of Wimborne Publishing. www.epemag.com Mobile Phone Switch – Freely phone home and control an appliance

THERE are several designs that the author has seen for controlling appliances remotely via a mobile phone, but they have all involved connecting a microcontroller to the serial port of the phone and either using the Caller ID, or parsing data from an SMS message. Not only are these devices complex to build, they are also specific to a particular model of phone.

The circuit prsented in Fig.1 is much easier and cheaper to build and should work on any mobile phone, as long as the screen lights up when it receives a call. The way it works is simple, the mobile phone receives a call causing its screen to light up, a lightdependent resistor (LDR) detects this and triggers a flip-flop (IC1) which turns a relay on or off, thus controlling the power to whatever is connected to the relay contacts.
Finally, as the circuit does not answer the call, nor receive an SMS message, there are no call charges incurred.

The circuit is based around a 4013 dual flip-flop IC, which is configured in such a way that its two outputs change state with each high-going pulse to its trigger input. LDR1, which is an ORP12 light dependent resistor, is placed so that it faces the screen of the mobile phone. The sensitivity of LDR1 can be adjusted by VRl.

When the phone rings and the screen lights up, the resistance of LDR1 falls, this turns on transistor TR1, which could be any sort of general purpose NPN transistor. Capacitor C1 acts as a smoothing capacitor, which maintains a continuous high logic level even if the screen on the mobile phone flashes when it rings. If the screen of the phone you are using doesn’t flash then this component can be omitted.

Resistor R2 pulls the input to IC1 low and also discharges C1 when the phone is not ringing. Transistor TR2 is controlled by the Q1 output of IC1 and is used to turn on or off the relay, RLAl, which controls the Live mains supply of the attached device.

LEDs D1 and D2 indicate whether the relay is on or off and diode D3 protects the circuit from the back EMF pulse induced at the moment that the relay coil is turned off. Switch Sl can be used to manually trigger the circuit and can be omitted if not required.

The whole circuit, along with the phone, should be mounted in a lightproof enclosure so it is not accidentally triggered by ambient light. If the circuit is to be in permanent operation then you should ensure the phone’s charger is connected to prevent the battery running out.

It is a good idea to use a brand new sim card, which can usually be obtained for free, or very little cost, from most of the major mobile network providers. This will make the circuit more reliable as only you will have the telephone number to operate the device. However, the circuit will still be triggered by the occasional wrong number, or text message sent by the network provider, so it shouldn’t be used to control any critical appliances.

Article reproduced by permission of Wimborne Publishing. www.epemag.com Mobile Phone Switch – Freely phone home and control an appliance

THERE are several designs that the author has seen for controlling appliances remotely via a mobile phone, but they have all involved connecting a microcontroller to the serial port of the phone and either using the Caller ID, or parsing data from an SMS message. Not only are these devices complex to build, they are also specific to a particular model of phone.

The circuit prsented in Fig.1 is much easier and cheaper to build and should work on any mobile phone, as long as the screen lights up when it receives a call. The way it works is simple, the mobile phone receives a call causing its screen to light up, a lightdependent resistor (LDR) detects this and triggers a flip-flop (IC1) which turns a relay on or off, thus controlling the power to whatever is connected to the relay contacts.
Finally, as the circuit does not answer the call, nor receive an SMS message, there are no call charges incurred.

The circuit is based around a 4013 dual flip-flop IC, which is configured in such a way that its two outputs change state with each high-going pulse to its trigger input. LDR1, which is an ORP12 light dependent resistor, is placed so that it faces the screen of the mobile phone. The sensitivity of LDR1 can be adjusted by VRl.

When the phone rings and the screen lights up, the resistance of LDR1 falls, this turns on transistor TR1, which could be any sort of general purpose NPN transistor. Capacitor C1 acts as a smoothing capacitor, which maintains a continuous high logic level even if the screen on the mobile phone flashes when it rings. If the screen of the phone you are using doesn’t flash then this component can be omitted.

Resistor R2 pulls the input to IC1 low and also discharges C1 when the phone is not ringing. Transistor TR2 is controlled by the Q1 output of IC1 and is used to turn on or off the relay, RLAl, which controls the Live mains supply of the attached device.

LEDs D1 and D2 indicate whether the relay is on or off and diode D3 protects the circuit from the back EMF pulse induced at the moment that the relay coil is turned off. Switch Sl can be used to manually trigger the circuit and can be omitted if not required.

The whole circuit, along with the phone, should be mounted in a lightproof enclosure so it is not accidentally triggered by ambient light. If the circuit is to be in permanent operation then you should ensure the phone’s charger is connected to prevent the battery running out.

It is a good idea to use a brand new sim card, which can usually be obtained for free, or very little cost, from most of the major mobile network providers. This will make the circuit more reliable as only you will have the telephone number to operate the device. However, the circuit will still be triggered by the occasional wrong number, or text message sent by the network provider, so it shouldn’t be used to control any critical appliances.

Article reproduced by permission of Wimborne Publishing. www.epemag.com