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Circuits > Oscillators and timers > 9 Second LED Timer and Relay Circuit
9 Second LED Timer and Relay Circuit
This circuit provides a visual 9 second delay using 10 LEDs before closing a
12 volt relay. When the reset switch is closed, the 4017 decade counter will be
reset to the 0 count which illuminates the LED driven from pin 3. The 555 timer
output at pin 3 will be high and the voltage at pins 6 and 2 of the timer will
be a little less than the lower trigger point, or about 3 volts. When the switch
is opened, the transistor in parallel with the timing capacitor (22uF) is shut
off allowing the capacitor to begin charging and the 555 timer circuit to
produce an approximate 1 second clock signal to the decade counter. The counter
advances on each positive going change at pin 14 and is enabled with pin 13
terminated low. When the 9th count is reached, pin 11 and 13 will be high,
stopping the counter and energizing the relay. Longer delay times can be
obtained with a larger capacitor or larger resistor at pins 2 and 6 of the 555
timer.
9 Second LED Timer and Relay Circuit
Title: 9 Second LED Timer and Relay Circuit
Source: unknown
Published on: 2007-07-21
Reads: 424
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Circuits > Oscillators and timers > 9 Second LED Timer and Relay Circuit |
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