Schematics > Oscillators and timers > 9 Second Digital Readout Countdown Timer
9 Second Digital Readout Countdown TimerThis circuit provides a visual 9 second delay using a 7 segment digital readout
LED. When the switch is closed, the CD4010 up/down counter is preset to 9 and
the 555 timer is disabled with the output held high. When the switch is opened,
the timer produces an approximate 1 second clock signal, decrementing the
counter until the 0 count is reached. When the zero count is reached, the 'carry
out' signal at pin 7 of the counter moves low, energizing the 12 volt relay and
stopping the clock with a low signal on the reset line (pin 4). The relay will
remain energized until the switch is again closed, resetting the counter to 9.
The 1 second clock signal from the 555 timer can be adjusted slightly longer or
shorter by increasing or decreasing the resistor value at pin 3 of the timer.
The CD4510 is a CMOS Presettable BCD Up/Down counter which can be preset to
any number between 0 and 9 with a high level on the PRESET ENABLE line, (pin 1)
or reset to 0 with a high level on the RESET line (pin 9). Inputs for presetting
the counter (P1, P2, P3, P4) are on pins (4, 12, 13, 3) respectively. The
counter advances up or down on each positive-going clock transition (pin 15) and
the counting direction (up or down) is controlled by the logic level on the UP/DOWN
input (pin 10, high=up, low=down). The CARRY-IN signal (pin 5) disables the
counter with a high logic level.
The CD4511 is a CMOS BCD to 7 segment latch decoder capable of sourcing up to
25 mA which allows it to drive LEDs and other displays directly. A LATCH-ENABLE
line (pin 5, active low) stores data from the BCD input lines. A LAMP-TEST input
(pin 3, active low) can be used to illuminate all 7 segments, and a BLANKING
input (pin 4, active low) can be used to turn all segments off. The LED display
must be a common cathode type so that the segments are illuminated with a
positive voltage on their respective connections.
9 Second Digital Readout Countdown Timer
Title: 9 Second Digital Readout Countdown Timer
Source: unknown
Published on: 2007-07-21
Reads: 557
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