Mobile Controlled Dtmf
IC 7805-
The input voltage must always be higher than the output voltage by some minimum amount (typically 1.5 to 2 volts) . 7805 is a linear voltage regulator, so it is not very efficient and it has drop out voltage problem. As they are based on a linear regulator design, the input current required is always the same as the output current. As the input voltage must always be higher than the output voltage, this means that the total power (voltage multiplied by current) going into the 78xx will be more than the output power provided. The extra input power is dissipated as heat. This means both that for some applications an adequate heatsink must be provided, and also that a (often substantial) portion of the input power is wasted during the process, rendering them less efficient than some other types of power supplies7805 IC has a thermal shutdown feature to protect the IC in case of overheating so it should be safe to use 7805 without a heatsink plate for less than 200mA load. However should your load cross 200mA, you should consider using a heatsink plate. Heatsink plate should be large enough to bring 7805 heat to such a level that you can comfortably touch it
The two capacitors used in the voltage regulator circuit are not mandatory but they are good to maximize voltage regulation.
BC548-
The BC548 is a general purpose epitaxial silicon NPN bipolar junction transistor
If the plastic package is held in front of one's face with the flat side facing toward you and the leads downward, (see picture) the order of the leads, from left to right is collector, base, emitter.
The transistor is initially in the cut-off region. When the DTMF decoder receives a valid signal, ‘DV’ of HT9170 goes high. This sends the transistor in saturation region & it behaves as a closed switch & the LED connected to it is lighted showing that a valid tone pair was received. The microcontroller accepts data from HT9170 only when the transistor is conducting i.e. the
The input voltage must always be higher than the output voltage by some minimum amount (typically 1.5 to 2 volts) . 7805 is a linear voltage regulator, so it is not very efficient and it has drop out voltage problem. As they are based on a linear regulator design, the input current required is always the same as the output current. As the input voltage must always be higher than the output voltage, this means that the total power (voltage multiplied by current) going into the 78xx will be more than the output power provided. The extra input power is dissipated as heat. This means both that for some applications an adequate heatsink must be provided, and also that a (often substantial) portion of the input power is wasted during the process, rendering them less efficient than some other types of power supplies7805 IC has a thermal shutdown feature to protect the IC in case of overheating so it should be safe to use 7805 without a heatsink plate for less than 200mA load. However should your load cross 200mA, you should consider using a heatsink plate. Heatsink plate should be large enough to bring 7805 heat to such a level that you can comfortably touch it
The two capacitors used in the voltage regulator circuit are not mandatory but they are good to maximize voltage regulation.
BC548-
The BC548 is a general purpose epitaxial silicon NPN bipolar junction transistor
If the plastic package is held in front of one's face with the flat side facing toward you and the leads downward, (see picture) the order of the leads, from left to right is collector, base, emitter.
The transistor is initially in the cut-off region. When the DTMF decoder receives a valid signal, ‘DV’ of HT9170 goes high. This sends the transistor in saturation region & it behaves as a closed switch & the LED connected to it is lighted showing that a valid tone pair was received. The microcontroller accepts data from HT9170 only when the transistor is conducting i.e. the