# 555/556 Timer Circuit

Discussion in 'Electronic Basics' started by DaveK, Feb 10, 2007.

1. ### DaveKGuest

I'm kind of new to this electronics stuff. I took a class years ago
and have a pretty good idea of how basic circuits work. I don't have a

I am working on a little project which I don't know how to set up. I
am using a 4.5VDC battery power source with a mercury switch that will
be used to close the circuit and sound a buzzer. What is happening is
that when the circuit closes the mercury will continue to slosh around
and sound the buzzer multiple times. What I would like to happen is
when the circuit closes it sounds the buzzer for a split second, opens
and stays open for a determined amount of time (3sec) even if the
mercury closes the circuit again. I was told I could use a 555 or 556
timer to accomplish that. I purchased both timers and set up a couple
basic circuits that I saw on the internet. I've played around with the
timers for a long time but I just can't figure out how to use them to
accomplish my above goal.

I would surely appreciate any information or what I would need to
purchase to get my circuit working. If you have any questions I would
be happy to answer them. You can reach me by e-mail
or phone 480-763-8199.

Dave Kofka

2. ### BobGuest

Dave,

It would help if you could provide a link to the circuit you're using, or
post the schematic in alt.binaries.schematics.electronic . It should be easy
figure out why it's not working.

The basic idea would be to use the first 555 to immediately fire and drive
the buzzer. This first 555's output would also fire the second 555. The
first 555 would timeout quickly and stop the buzzer. The second timer would
have a longer delay (3 seconds) and would inhibit refiring of the first 555
until the 3 seconds elapsed.

There may be a tricky way to do it with a single 555 but using two (or a
556) would be easier.

Bob

3. ### John FieldsGuest

---
View in Courier:
CR1
.. +------------------[<1N4148]--------------------+
.. | |
..+V---+---------+--|--+-------+---------------+-----+-------+ |
.. | R1 R2| | | |8 R3| | |8 |
.. [10K] [10K]|[Rt1] +---+---+ [10K] [Rt2] +---+---+ |
.. | | | | 2|_ Vcc |3 C2 | | 2|_ Vcc |3 |
.. +-[0.1µF]-+--+--|--O|T OUT|-+-[0.1µF]-+-----|--O|T OUT|--+
.. | C1 | 6| | | | 6| |
.. | O +---|TH | +----+ +---|TH |
.. | O S1 | 7|_ 555| | | 7|_ 555|
.. | +--O|D | | +--O|D |
.. | | | GND | [BUZZER} +| | GND |
.. | [Ct1] +---+---+ | [Ct2] +---+---+
.. | | U1 |1 | | U2 |1
..GND--+---------------+-------+----------+----------+-------+

When S1 closes it pulls the junction of R1 and C1 to ground, which
generates a momentary low going pulse at U1-2, the TRIGGER- input of
U1. This causes U1-3 to go high for:

Tout = 1.4 Rt1 Ct1

during which time the buzzer will sound.

When U1 times out, U1-3 will go low, generating a low-going pulse at
U2-2, which will cause U2-3 to go high for:

T = 1.4 Rt2 Ct2

When U2-3 goes high it will force U1-2 high and keep any extraneous
contact closures of S1 from triggering U1. When U2 times out it
will be disconnected from U1-2 by CR1 and the next S1 contact
closure will start the cycle anew.

4. ### John FieldsGuest

---
I left out a couple of diodes.

Here's the LTSPICE circuit list:

Version 4
SHEET 1 1972 1056
WIRE 96 16 -448 16
WIRE 208 16 160 16
WIRE 240 16 208 16
WIRE 416 16 320 16
WIRE -672 80 -832 80
WIRE -560 80 -672 80
WIRE 16 80 -560 80
WIRE 288 80 16 80
WIRE 416 80 416 16
WIRE 416 80 288 80
WIRE 736 80 416 80
WIRE -672 112 -672 80
WIRE -560 112 -560 80
WIRE 288 128 288 80
WIRE -272 160 -336 160
WIRE 16 160 16 80
WIRE 16 160 -48 160
WIRE 112 160 16 160
WIRE 448 160 384 160
WIRE 736 160 736 80
WIRE 736 160 672 160
WIRE 832 160 736 160
WIRE 112 192 112 160
WIRE 832 192 832 160
WIRE -672 224 -672 176
WIRE -560 224 -560 192
WIRE -560 224 -672 224
WIRE -368 224 -560 224
WIRE -272 224 -368 224
WIRE 16 224 -48 224
WIRE 208 224 208 16
WIRE 288 224 288 192
WIRE 288 224 208 224
WIRE 448 224 288 224
WIRE 736 224 672 224
WIRE -672 256 -672 224
WIRE -448 288 -448 16
WIRE -272 288 -448 288
WIRE 16 288 16 224
WIRE 16 288 -48 288
WIRE 448 288 272 288
WIRE 736 288 736 224
WIRE 736 288 672 288
WIRE 16 320 16 288
WIRE 112 320 112 272
WIRE 112 320 16 320
WIRE 736 320 736 288
WIRE 832 320 832 272
WIRE 832 320 736 320
WIRE -832 352 -832 80
WIRE -304 352 -832 352
WIRE -272 352 -304 352
WIRE 112 352 112 320
WIRE 448 352 416 352
WIRE 832 352 832 320
WIRE -832 432 -832 352
WIRE -672 432 -672 320
WIRE -448 432 -448 288
WIRE -304 432 -304 352
WIRE 416 432 416 352
WIRE 416 432 -304 432
WIRE -368 496 -368 224
WIRE -112 496 -368 496
WIRE 272 496 272 288
WIRE 272 496 -48 496
WIRE -832 544 -832 512
WIRE -672 544 -672 512
WIRE -672 544 -832 544
WIRE -448 544 -448 512
WIRE -448 544 -672 544
WIRE -336 544 -336 160
WIRE -336 544 -448 544
WIRE 112 544 112 416
WIRE 112 544 -336 544
WIRE 384 544 384 160
WIRE 384 544 112 544
WIRE 832 544 832 416
WIRE 832 544 384 544
WIRE -832 592 -832 544
FLAG -832 592 0
SYMBOL Misc\\NE555 -160 256 R0
SYMATTR InstName U1
SYMBOL voltage -672 416 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value PULSE(4.5 0 .1 1e-6 1e-6 .01 .05)
SYMATTR InstName V1
SYMBOL voltage -832 416 R0
WINDOW 123 0 0 Left 0
WINDOW 3 24 104 Invisible 0
SYMATTR Value 4.5
SYMATTR SpiceLine Rser=0
SYMATTR InstName V2
SYMBOL res 96 176 R0
SYMATTR InstName R2
SYMATTR Value 1e6
SYMBOL cap 96 352 R0
SYMATTR InstName C1
SYMATTR Value .5e-6
SYMBOL Misc\\NE555 560 256 R0
SYMATTR InstName U2
SYMBOL res 816 176 R0
SYMATTR InstName R4
SYMATTR Value 1e6
SYMBOL cap 816 352 R0
SYMATTR InstName C2
SYMATTR Value 5e-6
SYMBOL res 336 0 R90
WINDOW 0 -33 60 VBottom 0
WINDOW 3 -27 58 VTop 0
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL cap 96 32 R270
WINDOW 0 69 32 VTop 0
WINDOW 3 66 35 VBottom 0
SYMATTR InstName C3
SYMATTR Value .1e-6
SYMBOL cap -656 320 R180
WINDOW 0 24 64 Left 0
WINDOW 3 24 8 Left 0
SYMATTR InstName C6
SYMATTR Value .1e-6
SYMBOL res -576 96 R0
SYMATTR InstName R6
SYMATTR Value 10k
SYMBOL res -464 416 R0
SYMATTR InstName R1
SYMATTR Value 100
SYMBOL diode -48 480 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL diode -656 176 R180
WINDOW 0 46 30 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL diode 304 192 R180
WINDOW 0 -41 35 Left 0
WINDOW 3 -73 0 Left 0
SYMATTR InstName D3
SYMATTR Value 1N4148
TEXT -808 568 Left 0 !.tran 0 10s 0

5. ### romaGuest

See these delay circuits at :http://members.shaw.ca/roma/eighteen.html