go to main index know about us who we are and what we are provide ? we provide training on how to reach us send e-mail us







Auto Dialler Circuit







In this project we show that how we use the telephone as a electronics eye. With the help of landline phone we check and examine the position of the house automatically. In this logic we attach some sensor with the telephone and if there is any mis happening then telephone is automatic on and then circuit press the redial button of the telephone and then  telephone dial the  pre-dialied number and sense the voice message to the received end. All  these logic is to be divided into few parts.




Sensor unit.


Micro controller interface


Switch on the telephone


Redial the number



Transfer the message on the telephone line


Switch off the telephone line after sending the message.



In this sensor unit  it is our choice , how many sensorís  we use , IN this project we use two sensorís, In this project we use two electronics circuit with infra red sensorís and fire alarm sensor.


In the infra red sensor. We use ic 555 as a main component. Pin no 4 and pin no 8 is connected to the positive supply. Pin no 1 is connected to the negative voltage. One capacitor is grounded from the pin no 5 for noise cancellation. Output is available on the pin no 3. Sensor is connected to the pin no 2.


In the case of infra red sensor. Pin no 2 is negative bias through the 33k ohm resistor and pin no is positively biased through the photodiode. One infra red transmitter l.e.d is  focused to the photodiode . Infra red l.e.d is directly connected to the positive and negative supply through the 470 ohm resistor..


In normal stage when light is focus on the photodiode then  pin no 2 is positively biased photodiode. If pin no 2 is positive then  negative  output is available on the pin no 3. Now when any body interrupt the light then  there is no light on the photodiode and pin no 2 is now gets its voltage from only 33 k ohm resistor.  If pin no 2 is become negative then  output is shifted to the  pin no 3. when positive output is available on the pin no 3 and with the help of this voltage  NPN transistor is on and npn transistor provide a negative voltage as a pulse to the microcontroller.


If we connect two sensor as a input to the microcontroller then we use same circuit with the ic 555 .

 Note that microcontroller sense only negative input to the microcontroller.







ATMEL AT89C2051 Pinout and Description

The 2051 is a low voltage (2.7V - 6V), high performance CMOS 8-bit microcontroller with 2 Kbytes of Flash programmable and erasable read only memory (PEROM). This device is compatible with the industry standard 8051 instruction set and pinout. The 2051 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications. The 2051 provides the following features:

~ 2 Kbytes of Flash
~ 128 bytes of RAM
~ 15 I/O lines
~ two16-bit timer/counters
~ five vector, two-level interrupt architecture
~ full duplex serial port
~ precision analog comparator
~ on chip oscillator and clock circuitry

In addition, the 2051 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port and interrupt system to continue functioning. The Power Down Mode saves the RAM contents but freezes the oscillator disabling all other chip functions until the next hardware reset.

To learn how to use the 2051 microcontroller, get the Microcontroller Beginner Kit (click here)

2051 - 24MHz DIP Available

The 2051 can be programmed using a device programmer such as the PG302 (Click Here).

We also have Projects that use the 2051 Microcontroller.
See the Intermediate Tutorial Section.

This page last updated on April 7, 2003.




All the input sensor is connected to the pin no 18 and 19. Pin no 18 is connected to the P1.6, and pin no 19 is connected to the P1.7. pin no 20 is connected to the positive supply. Pin no 1  reset pin. One capacitor is connected from positive to pin no 1 and one resistor is  grounded from pin no 1. One microswitch is connected  across the  capacitor fro manual reset switch.


One buzzer is connected to the pin no 16 ( Port p1.4) this buzzer is on when  circuit sense a input from the  input sensorís. .

Microcontroller sense the input  and then  we switch on the telephone line optocoupler. Here we use 817 optocoupler. Once the optocoupler is on one 270 resistor is connected in parallel with the  telephone line. After this we press the flash button of the telephone dialer circuit. For flash purpose we provide a negative pulse  to the flash point for this we  CLR P1.1  and after some delay we SET the P1.1 and after pressing the flash button we press the redial number. For this we press the pin no 12 ( port p1.0)  and after  some delay again we set the P1.0


 After pressing the flash button, redial button and switch on the telephone line we switch on the memory ic. We press the pin no 24 of the isd 1420. ISD 1420 is a voice processor  ic.  Output from the voice processor is available on the pin no 14 and 15 and this output is coupled to the transformer and output from this transformer is  connected to the telephone line. At the same time telephone dialer ic provide a   pulse of the telephone number to the telephone line.


Telephone dialer circuit.

 In this portion of telephone dialer circuit we  use the   telephone dialer circuit.  For this we use one dtmf generator circuit to generate a dtmf tones from the circuit. For this purpose we use one DTMF generator circuit to generate a dtmf tones from the circuit. We connect one telephone keypad  or push to on switches with this circuit. We use total 14 push to on switches with this circuit to dial the dtmf tones. Once we dial the number in the  dialer circuit. Now when micrcontroller press the redial switch then circuit is on and  redial the  pre-dial number .

All the switches are connected to the pin no no 12,13,14,15,16,17,18. All the switches are connected in row and matrix combination including redial and flash switch




In DTMF there are 16 distinct tones. Each tone is the sum of two frequencies: one from a low and one from a high frequency group. There are four different frequencies in each group.

Your phone only uses 12 of the possible 16 tones. If you look at your phone, there are only 4 rows (R1, R2, R3 and R4) and 3 columns (C1, C2 and C3). The rows and columns select frequencies from the low and high frequency group respectively. The exact value of the frequencies are listed in Table 3 below:

TABLE 3: DTMF Row/Column Frequencies




R1: ROW 0


R2: ROW 1


R3: ROW 2


R4: ROW 3






C1: COL 0


C2: COL 1


C3: COL 2


C4: COL 3


C4 not used in phones


Thus to decipher what tone frequency is associated with a particular key, look at your phone again. Each key is specified by its row and column locations. For example the "2" key is row 0 (R1) and column 1 (C2). Thus using the above table, "2" has a frequency of 770 + 1336 = 2106 Hz The "9" is row 2 (R3) and column 2 (C3) and has a frequency of 852 + 1477 = 2329 Hz.

The following graph is a captured screen from an oscilloscope. It is a plot of the tone frequency for the "1" key:


You can see that the DTMF generated signal is very distinct and clear. The horizontal axis is in samples. The frequency of the tone is about 1900 Hz - close to the 1906 Hz predicted by Table 3 (697+1209).




CIRCUIT DIAGRAM USE IN THIS PROJECT FOR TELEPHONE DIALLER IS GIVEN BELOW. In this circuit we use ic 91215  as adtmf generator. Pin no 15,16,17,18 is a row and pin no 12,13,14 is a row. All the switches are connected to these pins. Redial button and flash button is connected to the microcontroller output pin s no 13 and 12 . Output from the  91215 is available on the pin no 7 of the  ic . Output from the 91215 is further amplify by the  ic 741. Here pin no 7 of the ic 741 is connected to the positive supply and pin no 4 is connected to the negative supply. Pin no 6 is the output pin and amplify signal is available on this pin and again further amplify by the two transistor circuit. Output from the transistor circuit is connected to the one coil of the output transformer.

Now when we press a redial number then 91215 generate a pre-dial tones and this signal is further  connected to the coil and further pass on the telephone line.


Components required:


Ic 91214


push to on sw

555 timer

 .001 Ķf,0.1 Ķf,0.01Ķf



crystal 11.0592 MHz

3.38 MHz.


condenser Mic

speaker 8 ohm

relay 12v 100 ohm

transformaer 6v 500mA

infrared Sensor,

heat Sensors

connecting wires

copper clad board
































Easy to implement


Low cost,

Components easily available in market.



Home security

Car security

In hospital patient security

Machine monitoring


www.ludhianaprojects.com/auto dialler.doc