Composed and Submitted by: Jennifer Goldy
IC MM74C926 is inside comprised of a 4-digit counter, a yield hook up stage, a npn yield in charge of sourcing driver systems for regular cathode, 7-portion show and an inner multiplexing hardware with four multiplexing yields.
The multiplexing circuit organize additionally incorporates an in-manufactured free running oscillator, and does not depend on any extra outside recurrence producing system.
The counter is intended to continue on a negative climbing of the clock signals.
The clock sign is fabricated by the clock IC LM555 (IC1) and inspired over stick 12 of IC2.A higher flag on reset stick 13 of IC2 resets the IC to zero rationale.
Reset stick 13 is connected with +5V by method for a reset push-on-switch S3.
The minute S2 is pressed actually for a small amount of a second, the tally figure is rendered to a zero rationale, transistor T1 reacts with a trigger and it resets IC1.
This implements the including to begin a circumstance wherein S2 is in "off" condition.
A low logic signal on the latch-enable input pin 5 (LE) of IC2 latches the count in the counter module into the on chip set output latches.
In an event when switch S2 is switched ON, pin 5 is forced to go low and thereby the count figure is allowed to be saved in the latch section of the IC.
Display-select pin 6 (DS) ascertains if the figure on the counter or the stored count in the latch may be shown on the display or not.
In case pin 6 is held low the figure in the output latch section is enabled to get displayed, however if pin 6 is rendered with a high logic the count stored in the counter is illuminated over the connected display.
On an occasion when switch S2 is switched, the base of pnp transistor T2 is linked with ground ensuring that it begins operating. The emitter of T2 is rigged with DS pin of IC2.
Consequently, whenever switch S3 is switched ON, reset pin 13 of IC2 is coupled with negative through the transistor T1 making sure that the oscillator is inhibited from generating clock pulses. This operation is executed to implement a synchronization between IC1 and IC2.
At the first level, reset the module in order to enable the display to show ‘0000.’ Next disconnect switch S2 for the stop watch to initiate its counting the periods. In case you wished to inhibit the clocking of the chip, simply switch OFF the control S2.
The given rotary switch S1 may be opted for selecting the many different time intervals at the output of the astable multivibrator (IC1).
The design will work off a 5V supply inputs. The circuit may be easily fixed and built on a general-purpose PCB.
You may want to enclose the entire circuit in a metallic cabinet with slots built for four 7-segment displays, rotary switch S1, start/stop switch S2 and reset switch S3 in the dashboard plate of the selected encloser.