LCD based digital alarm clock

An alarm clock is a clock that indicates a pre-set time by producing sound at that time. This functionality of digital clock is used to awaken people or remind them of something. This circuit is an extension to the digital clock with time setting option. Here an extra switch is provided to set the alarm. While the alarm is set, the clock time does not stop and runs in the background.The circuit is build around 8051 micro-controller (AT89C51) and uses LCD to display time.

Celsius and fahrenheit scale digital thermometer using AT89C51

Fahrenheit scale digital thermometer is a temperature indicator which displays temperature in Fahrenheit scale. It is similar to Celsius scale digital thermometer, except a little modification in the microcontroller program. The temperature sensed in Celsius scale in the Celsius scale thermometer project is converted into the Fahrenheit scale temperature just by using the Celsius to Fahrenheit conversion formulae. This project also uses 8051 microcontroller (AT89C51).

Simple Digital clock using 8051 microcontroller (AT89C51)

A digital clock is one that displays time digitally. The circuit explained here displays time with two ‘minutes’ digits and two ‘seconds’ digits on four seven segment displays. The seven segment and switches are interfaced with 8051 microcontroller AT89C51. This circuit can be used in cars, houses, offices etc.

Automatic bidirectional visitor counter using 8051 microcontroller (AT89C51)

A counter that can change its state in either direction, under control of an up–down selector input, is known as an up–down counter. The circuit given here can count numbers from 0 to 9999 in up and down modes depending upon the state of the selector. It can be used to count the number of persons entering a hall in the up mode at entrance gate. In the down mode, it can count the number of persons leaving the hall by decrementing the count at exit gate. It can also be used at gates of parking areas and other public places.
This circuit divided in three parts: sensor, controller and counter display. The sensor would observe an interruption and provide an input to the controller which would run the counter in up/down mode depending upon the selector setting. The same count is displayed on a set of 7-segment displays through the controller.

interface 16x2 LCD with 8051 microcontroller

Interface a keypad with Microcontroller

Keypad is a widely used input device with lots of application in our everyday life. From a simple telephone to keyboard of a computer, ATM, electronic lock, etc., keypad is used to take input from the user for further processing. In this article we are interfacing keypad with the MCU AT89C51 and displaying the corresponding number on LCD. This module can be further used in a number of systems to interfaced keypad with microcontroller and other processors to get desired output.

Keypad is organized as a matrix of switches in rows and column. The article uses a 4X3 matrix keypad and a 16x2 LCD for displaying the output of keypad.
The circuit diagram shows the connection of keypad with the controller. Port P2 of the microcontroller is used to send the data for displaying on the LCD. P1^1, P1^2, P1^3 pins of microcontroller is connected to RS, RW, EN pins of LCD respectively. Port P0 is used to scan input from the keypad (refer circuit diagram for connection).

The concept of interfacing keypad with the MCU is simple. Every number is assigned two unique parameters, i.e., row and column number (n(R, C) for example 6 (2, 3)). Hence every time a key is pressed the number is identified by detecting the row and column number of the key pressed.

Initially all the rows are set to zero by the controller and the columns are scanned to check if any key is pressed. In case no key is pressed the output of all the columns will be high.

Internal block diagram of DACO800

• The DAC0800 is an 8-bit, high speed, current output DAC with a typical settling time (conversion time) of 100 ns.

• It produces complementary current output, which can be converted to voltage by using simple resistor load.

• The DAC0800 require a positive and a negative supply voltage in the range of ± 5V to ±18V.

• It can be directly interfaced with TTL, CMOS, PMOS and other logic families.

• For TTL input, the threshold pin should be tied to ground (VLC = 0V).

• The reference voltage and the digital input will decide the analog output current, which can be converted to a voltage by simply connecting a resistor to output terminal or by using an op-amp I to V converter.

• The DAC0800 is available as a 16-pin IC in DIP