Microcontroller Based Caller ID & Use of DS1232

A Practical Application using Microcontroller – Caller ID

Caller ID is known as caller identification (CID), it is a telephone service to transmit a caller’s number to the called person phone soon after the call is replied. Where, caller ID can additionally furnish the name of the calling person if available. The caller ID could be shown on the phone display or on a separate display device which is connected to it.

Caller ID is a characteristic of digital telephone network, by which the phone number of the calling person can be transferred, using the standard phone line to the called person before he/she responses the call. There are two different caller ID signaling systems, in which data is sent between the first and second phone ring signal bursts. Furthermore the number information is transmits using standard DTMF signals. The microcontroller is used to control the total system.

The incoming and the dialed numbers are displayed on the LCD display. The Microcontroller is used to control the whole system. It gets the numbers through the DTMF decoder and displays it over the LCD.

Small Notes on DTMF:

There are two types of dialing systems: Pulse dialing and tone dialing. Tone dialing system is a general dialing system and faster than the pulse dialing system. DTMFs are used in telephone line system and also used to control the telephone systems. The DTMF system consists mainly low and high frequency bands for each number, according to these frequencies the signals can be transferred to the system. When a number is pressed on telephone then a tone will generate.

Specifications and Standards of Caller ID:


There are two types of caller ID signaling systems. The numbering systems consist, country code (CC) and national significant number (NSN). For example, in the phone number 91-9885098850, the country code is “91” and national significant number is “9885098850”. The national significant number consists of an area code and the subscriber number.

callerThe calling number information and called number information is transferred in following format:

caller IThe information passed through as DTMF tone sequence. From the above figure, first calling number is transmitted by the sequence of forwarded number sequence followed by information code. Here A and B indicates the start of the calling and forwarded number. If there are more forwarded numbers then they transmitted alternatively. And C is the end of transmission.

The Main Features of the Caller ID Device:

  • Showing of the calling phone number before the call is answered
  • Maintaining a log of all the unanswered calls as well as the time and date of the call
  • Displaying the number dialed by the user and duration of the call
  • Display of time and date when the device is idle
  • Enabling the user to adjust the date and time using the pushbutton

Block Diagram of Caller Id using 8051 and Working:

Microcontroller is the most important component in caller ID system. It is used for many reasons. The 8051 is the 8-bit controller, we can program very easily. It has 4Kb of flash memory, 128 bytes of on-chip RAM.

caller IDMicrocontroller plays main role in caller ID system; it controls the whole system components completely mainly DTMF and LCD display. The main function of the device is to receive the DTMF signals representing to the caller ID information from the telephone line and to decode them into corresponding binary codes. A cell phone is connected from its ear phone socket to the DTMF decoder for receiving the data. These codes are then transferred to the microcontroller. The processed data is then given to the parallel connected seven segment displays.

A way to test the Power Supply to the Microcontroller Based System – Using DS1232

DS1232 is a micro-monitor chip, which is used to monitor and control the power supply and software execution of a microcontroller based system and to provide a push-button reset. It mainly works on three virtual conditions:

  1. First, a precision temperature compensated reference and comparator circuit monitors the status of Vcc.
  2. Second function is to perform push-bottom reset control.
  3. The third function is a watchdog timer that forces the reset signals to active state if the strobe input is not driven low prior to time out.

When Vcc returns to an in-tolerance condition, the reset signals are kept in the active state for a minimum of 250ms to allow the power supply and processor to stabilize.

The DS1232 is available in 8-pin and 16-pin configuration. Here we are only going to see about 8-pin DS1232.

DS1232DS1232 Pin Description


  • Stops and restarts the microprocessor when it is out of control
  • 8-pin DIP with space saving
  • Removes the separate components
  • The microprocessor will restart automatically when power comes
  • If external override occurred then it controls the pushbutton
  • The supply power is controlled 5% or 10%
  • Microprocessor will stay ideal when checking the power transients

Application of DS1232:

The circuit below shows how the DS1232 is used with a DS87C520 Microcontroller.


From the circuit, a pull-up resistor is for the active low output and a decoupling capacitor to reduce the possibility of noise on the power supply causing a reset. The RST output of the DS1232 is not required by the microcontroller. The LEDs are used to signal when ISRs (Interrupt Service Requests) are being serviced.

When the active high reset signal rises with VCC and remains high between 250 ms and 1 second. The active low reset remains 0V until the delay elapses and then is pulled high by the pull-up resistor. The pull-up resistor is required because RST is an open collector output. Usually, RST and requires about 450 ms to become inactive. If reset signal is inactive, the microcontroller must strobe the ST signal low before the watchdog timer elapses. The DS1232’s watchdog timer cannot be disabled, so this must occur within n ms of the reset signals becoming inactive or the microprocessor will be reset. The DS1232 monitors VCC at all times and resets the microcontroller if the voltage drops below VCCTP (VCC trip point). VCCTP can be programmed to 5% or 10% below VCC and the micro monitor will hold the reset signals active for 250 ms to 1 second after VCC recovers and returns above VCCTP. VCCTP is programmed with the TOL pin.