Digital Stopwatch With 7-segment Schematic

You may have heard or seen such an object called Stopwatch hour. Stopwatch function to find out how long it takes in an activity. Usually the stopwatch is used in a variety of races: race, swimming, or even racing.

Stop watch is made ​​with a digital timer IC LM555 and IC MM74C926 4 digit counter with multiplexed 7-segment LED. MM74C926 consists of 4 digit counter, an internal output latch, NPN output for controlling the source of common cathode, 7-segment display and an internal multiplexing circuitry with four multiplexing outputs. Counter the negative edge clock face. Clock continually be produced by the timer IC LM555. The circuit works with a 5V power supply. It can be easily assembled on the PCB. Enter the circuit in a metal box with provisions for the 7-segment display, turn the switch S1, start / stop switch and reset switch S2 S3.

Digital Stopwatch reset the circuit by pressing S3 so now the display shows '0000 '. Open switch S2 to stop watch to start counting time. If you want to stop the clock, close S2. Rotary switch S1 is used to select different time periods on the output of the astable multivibrator (IC1).

Knight Rider Running Light Schematic

4017 Knight Rider circuit, the 555 is wired as an oscillator. It can be adjusted to give the desired speed for the display. The output of the 555 is directly connected to the input of a CD 4017.

Part List :

R1 22kΩ

R2 220Ω

VR1 50kΩ Preset

C1 1µF 16V

C2 0.01µF (103)

C3 10µF 16V

D1 – D10 1N4148

D11 – D16 LED

IC1 NE 555

IC2 CD 4017

The input of the counter is called the CLOCK line (555). The 10 outputs become active, one at a time, on the rising edge of the waveform from the 555. Each output can deliver about 20mA but a LED should not be connected to the output without a current-limiting resistor (220Ω in the circuit above).

The first 6 outputs of the chip are connected directly to the 6 LEDs and these “move” across the display. The next 4 outputs move the effect in the opposite direction and the cycle repeats. The animation above shows how the effect appears on the display. Using 6 LEDs, the display can be placed in the front of a model car to give a very realistic effect.