When stopping in the H condition, the BR terminal of each counter runs out in the L condition. When making the counter stop, it makes the count-down terminal stop in the L level condition. The stop of the count-down is done in making the input of N3 the L level. When becoming at 0вЂ™0вЂі, the count-down is made to stop. In addition from the clock generator, the pulse in the 1 second is inputted to the count-down terminal (DW) of the counter and the count-down is done. Only when the BR terminal of all counters becomes the L level, the output of the NAND gate becomes the L level. The BR signal of each counter is reversed by the inverter and is inputted to the NAND gate. No change can be seen.ДЇor the count out detector (Figure 3), the L level is output by the BR, terminal of the counter when the count value becomes 0. The output of the counter becomes вЂњ9вЂќ momentarily but it is immediately set to вЂњ5вЂќ. After that, the countdown is done from 5. Because вЂњ5вЂќ was already set to the counter, there has no (or very minimal) effect. With it, the output of the NAND gate becomes the H level. The output of the counter becomes вЂњ5вЂќ when вЂњ5вЂќ is set to the counter. The circuit this time set вЂњ5вЂќ as the presetting. The input of the presetting is set to the counter when the LD becomes the L level. For this part, the output of the NAND gate becomes in the L level when the 10th of the second display becomes 9. The point in the second counter circuit is to make the 59 seconds next of the 00 seconds. Next is the second counter circuit section (Figure 2) where 74HC192 is being used. The BCD (Binary Coded Decimal) counter is the counter which handles from 0 to 9. The condition of the LD is controlled with the control circuit which is controlling the operation of the timer. When the LD is not in the H condition, the counter does not work. At the time of this condition, because the value which is the same as the set value of BCD-SW spreads through the display part, too, you can confirm the set value in the display part. When the LD (load) terminal is in the L condition, the original value of the counter can be set with BCD-SW. The counter of the upper places is count-downed by the change of such BR. Next, it changes into H (the high level: +5V) when the counter becomes 9. The output of the BR (Borrow) becomes the L (the low level: 0V) when the counter becomes 0. The counter is count-downed by the low to high transition of the signal. The pulse signal (being the once per minute) from the second counter is inputted to DW (Count Down). There is 74HC190 in the counter which can be down in the count which is used as the clear terminal as the second counter. In the configuration of the minute counter (Figure 1), the 74HC192 (Presettable Synchronous Up/Down BCD Counter) is used as the counter. When using the 3 terminal voltage regulator, donвЂ™t supply the +5 V power supply from outside.В When supplying +5 V from outside, do not mount the 3 terminal voltage regulator. It uses the 3 terminal voltage regulator to work at only +12 V. The timer is supplying +12 V and +5 V separately is the power supply. This countdown timer circuit can be subdivided into four sections namely, the minute counter circuit, the second counter circuit, the count out detector, and the start/stop control circuit. We will be showing in the following pages the circuit schematic diagram, what components are to be used, and how the circuit operates.ДЇigure 1: Minute counter circuit, Figure 2: Second counter circuit, Figure 3: Count out detector, Figure 4: Start/Stop control circuitДЇigure 6:В Actual MultiSim 01 Simulated Circuit It can be used in sports, games, and in other areas.

This timer can be used in different activities. Countdown timers can be started and then stopped at any time and then the display will be showing how much time had passed in between. This is only one of the many useful things that can be created with this component. The group has chosen to create the digital project, Countdown Timer, in order to show one of the applications of the seven-segment decoder. It can be easily read because it easily catches the eye. For example, with a seven-segment decoder display, it is easier to read the time in a digital clock than with an analog one. It is most commonly used in digital clock displays, clock timers, and others. This can be used in displaying letters or numbers.

The seven-segment decoder is used in many applications. Uy, for our ECE 130 вЂ“ Computer Application class way back Augat University of St. вЂњCountdown Timer CircuitвЂќ is a project submitted by my group, namely, M. Posted on FebruUpdated on February 16, 2012

Countdown timer circuit schematic