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.
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 microcontroller receives a high signal at input port ‘P1.4’
The relay takes advantage of the fact that when electricity flows through a coil, it becomes an electromagnet. The electromagnetic coil attracts a steel plate, which is attached to a switch. So the switch's motion (ON and OFF) is controlled by the current flowing to the coil, or not, respectively. A very useful feature of a relay is that it can be used to electrically isolate different parts of a circuit. It will allow a low voltage circuit (e.g. 12VDC) to switch the power in a high voltage circuit (e.g. 100 VAC or more). The relay operates mechanically, so it can not operate at high speed. There are many kinds of relays-
1. Electromagnetic relay
2. Power Relay.
3. Time Delay Relay.
4. Latching Relay.
5. Crystal Can Relay.
6. Co-axial Relay.
The relay we r using are normally-open relays……i.e. the load circuit is open normally & when the contrl circuit is energized the load circuit closes.
Basic 5 Pin Mini Relay
Case size: 1 inch x 1 inch x 1 inch
Pin 30: Power into the relay for the accessory device
Pin 87: Relay switched power out to the accessory device
Pin 87a: Powered hot when relay is at rest. Open when relay is activated Pin 85: Positive hot line to activate the relay coil
Pin 86: Ground line to the relay
Is the relay driver I.C.
Link: Read Pg 10,11,12 from relay pdf file. i.e. read about de-spiking diode.
The Intel 8051 is used in embedded systems
4k bytes ROM for the program
128 BYTES of RAM for variables
32 I/O lines ( 4 PORTS WITH8 EACH )
1 Serial port
6 interrupt sources
16 bit address line
8051 contains four I/O ports (P0 - P3)
Each port can be used as input or output(bi-direction)
Intel's original MCS-51 family was developed using NMOS technology, but later versions, identified by a letter C in their name (e.g., 80C51)...
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