Simple delay circuit

Hi there

Im looking to build a delay circuit. Basically i want to be able to
close a switch which activates a 5 - 10 second delay. Then after the
delay i want it to turn on an alarm, until the switch is open again.

Ive been suggested to use a 555 timer, but it looks like after the
delay the alarm would either oscillate or it would only stay on for x
amount of seconds.

Is there any delay circuit out there that will keep the alarm on until
i open the switch again??

thanks for any help

cheers, dom

ive found this circuit:
http://img327.imageshack.us/img327/5206/r844gs.gif

Would that do the trick? I assume i attach a 9v battery on pins 8 and 1
of the 555.

How would i connect the alarm to pin 3? Also do i need to connect
anything to pin 2

thanks for any help

cheers, dom

On 5 Apr 2006 06:46:34 -0700, "(E-Mail Removed)"
<(E-Mail Removed)> wrote:

>ive found this circuit:
>http://img327.imageshack.us/img327/5206/r844gs.gif
>
>Would that do the trick? I assume i attach a 9v battery on pins 8 and 1
>of the 555.

---
That won't work for you since that's just the standard way to
generate an output pulse. The battery does attach to pin8 (+) and
pin 1 (-).
---

>How would i connect the alarm to pin 3? Also do i need to connect
>anything to pin 2

---
Yes to both questions, but since you had to ask, why don't you
describe in detail what you're trying to do?

That is, what's the application, what voltage do you want this thing
and the alarm to run on, how much current does the alarm need, and
can the switch open instead of closing in order to start the delay?


--
John Fields
Professional Circuit Designer

(E-Mail Removed) wrote:
> ive found this circuit:
> http://img327.imageshack.us/img327/5206/r844gs.gif
>
> Would that do the trick? I assume i attach a 9v battery on pins 8 and 1
> of the 555.
>
> How would i connect the alarm to pin 3? Also do i need to connect
> anything to pin 2
>
> thanks for any help
>
> cheers, dom

Hi, Dom. One easy way to get additional use out of the 555 is to
include other things in the circuit -- like your switch, for example,
and a relay. Assuming you've got a power supply between 5 and 15VDC,
you can get hold of a relay with a coil of the same voltage that uses
less than 100mA and you could try something like this (view in fixed
font or M$ Notepad):

|
| SW1
| VCC-o
| __--o----o----------o----------o-----o------o---.
| GND-o | | | | | |
| | | | | | |
| 33K.-. | | | | |
| | | | | | | |
| | | | | | | |
| '-' | | | | |
| | | .---o-----o--. | |
| o----------)------o2 8 4 | D| C|
| .001uF | | | | - C|
| --- | | | ^ C|
| --- .-----o | | | | RY1
| | | | | 3o---o---. .---o
| === | | | | |
| GND | .-. | | |
| - R | | | 555 | -----
| D ^ | | .--o6 | -----
| | '-' | | | |
| | | | | | |
| '-----o---o--o | '---o
| C | |7 |
| --- | |
| --- | |
| | | |
| === | |
| GND | 1 5 |
| '---o----o---'
| |
| ===
| GND
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The 555 can source or sink current (allegedly up to 200mA, but I'd keep
it to 50mA -- the output voltage bogs way down when you go over that).
This trick will ensure an easy, reliable delay-on relay contact for
your alarm you can wire up just like a switch. Here's how it works:

When your switch makes contact, the circuit is powered up. The 555 is
instantly triggered by the 33K resistor and the .001uf cap with a short
pulse as the cap charges up. The output of the 555 (pin 3) also goes
to Vcc instantaneously (in relay time). This keeps the relay from
turning on, because the other end of the coil is also connected to your
voltage. After the time period you choose by your R and C (68K and
100uF will give you about 8 seconds), the 555 output will go low. This
will apply voltage across the relay coil, so it will turn on. You can
wire the relay contacts up to your alarm just like a switch, so your
alarm will go on after the 8 seconds. It will stay on until you remove
the power, because the 555 will only trigger when the trigger pin (2)
goes low. That won't happen as long as there's power.

Note that when you turn the Single Pole Double Throw switch (SPDT) off,
the power connection is grounded. That removes voltage from the relay,
and discharges the timer cap C through the diode (both Ds can be
1N4001). If you have a SPST (Single Pole Single Throw) switch, just
load Vcc down by putting an extra 1K resistor from pin 8 (Vcc) to pin 1
(GND) to help discharge things when the switch opens.

I hope this has been of help. If you've already got the 555, and you
can scrounge a small relay, you should have your alarm working right
away. If you have any more questions, feel free to ask.

Good luck with your project
Chris

Hi there thanks for the info

I'm looking to make a sonic 'grenade'. Basically i'll have an alarm
salvaged from a rape alarm running off a 9v battery. I'll put the 'pin'
out, closing the switch. Then a short delay of around 10 seconds will
do, before the alram goes off. Preferably i would like the alarm to
stay on, until the switch is opened again

Not sure about the operating current though. Oh, and yes the switch
could be opened or closed i suppose, whichever is easiest

thanks for the info guys

cheers, dom

(E-Mail Removed) wrote:
> Hi there thanks for the info
>
> I'm looking to make a sonic 'grenade'. Basically i'll have an alarm
> salvaged from a rape alarm running off a 9v battery. I'll put the 'pin'
> out, closing the switch. Then a short delay of around 10 seconds will
> do, before the alram goes off. Preferably i would like the alarm to
> stay on, until the switch is opened again
>
> Not sure about the operating current though. Oh, and yes the switch
> could be opened or closed i suppose, whichever is easiest
>
> thanks for the info guys
>
> cheers, dom

Hi, Dom. I'd guess your piezo alarm probably uses less than 200mA.
You should be able to use just about any small relay which will operate
with 9V across the coil.

If you happen to be around a Radio Shack, try their Catalog #: 275-005
relay, which states a coil resistance of 500 ohms, and will operate on
a coil voltage of 9VDC. They're asking $4.29 USD for the thing.
Together with the 555 circuit above again, all components available at
Radio Shack), the circuit should use quite a bit less current than the
piezo alarm itself.

However, if you're going to be using a 9V transistor battery, you could
significantly extend the battery life by using a PNP transistor instead
of the relay, like this:

|
| SW1
| VCC-o
| __--o----o----------o----------o-----o--------------.
| GND-o | | | | |
| | | | | |
| 33K.-. | | | |
| | | | | | |
| | | | | | |
| '-' | | | |
| | | .---o-----o--. |
| o----------)------o2 8 4 | |
| .001uF | | | | |
| --- | | | |
| --- .-----o | | ___ |<
| | | | | 3o---|___|-| 2N3906
| === | | | | 1K |\
| GND | .-. | | |
| - R | | | 555 | |
| D ^ | | .--o6 | .---o---.
| | '-' | | | | |
| | | | | | | Piezo |
| '-----o---o--o | |Element|
| C | |7 | | |
| --- | | '---o---'
| --- | | |
| | | | ===
| === | | GND
| GND | 1 5 |
| '---o----o---'
| |
| ===
| GND
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

This will save most of the relay coil current. Note the 2N3906 is also
available at Radio Shack.

Good luck with your project
Chris

On 5 Apr 2006 11:04:19 -0700, "(E-Mail Removed)"
<(E-Mail Removed)> wrote:

>Hi there thanks for the info
>
>I'm looking to make a sonic 'grenade'. Basically i'll have an alarm
>salvaged from a rape alarm running off a 9v battery. I'll put the 'pin'
>out, closing the switch. Then a short delay of around 10 seconds will
>do, before the alram goes off. Preferably i would like the alarm to
>stay on, until the switch is opened again
>
>Not sure about the operating current though. Oh, and yes the switch
>could be opened or closed i suppose, whichever is easiest
>
>thanks for the info guys

---
Here's a simple way to do it if you can reverse the sense of the
switch. That is, have it open to start the delay. View in Courier:


+9V----+---------+----------+-------+
| | |K |
| | [1N4001] [ALARM]
| E | |
| 2N2907 B--[1K]--+-------+
| C |
| | |
[100K] [1K] |
| | C
+---------+--------B 2N4401
|+ | E
[1200µF] O| |
| |NC |
| O| |
| | |
GND>---+---------+----------+

You'll have to change the 2N4401 for something that can handle the
current if your alarm draws more than about half an amp. the 1N4001
is in there in case your alarm is inductive or if you want to drive
a relay with the circuit, in which case you could do this:

+9V----+---------+----------+-------+
| | |K | O--->COM
| | [1N4001] [COIL]- - -|
| E | | O--> |
| 2N2907 B--[1K]--+-------+ |
| C | +-------->NO
| | |
[100K] [1K] |
| | C
+---------+--------B 2N4401
|+ | E
[1200µF] O| |
| |NC |
| O| |
| | |
GND>---+---------+----------+

and use the relay to drive the alarm.


--
John Fields
Professional Circuit Designer

ive had the same prob needing a 30second to 60
for a automation project, so built my own.
ajustable from 0-60sec to delay switch on
wile the pc boots so my relays dont flicker.
no 555 timer in this circuit.
just a large cap to do the timeing.
i could send a circuit to youre
email if you want it.

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
> Hi there
>
> Im looking to build a delay circuit. Basically i want to be able to
> close a switch which activates a 5 - 10 second delay. Then after the
> delay i want it to turn on an alarm, until the switch is open again.
>
> Ive been suggested to use a 555 timer, but it looks like after the
> delay the alarm would either oscillate or it would only stay on for x
> amount of seconds.
>
> Is there any delay circuit out there that will keep the alarm on until
> i open the switch again??
>
> thanks for any help
>
> cheers, dom
>

On Thu, 6 Apr 2006 18:57:02 +1000, "crazy frog"
<(E-Mail Removed)> wrote:

>ive had the same prob needing a 30second to 60
>for a automation project, so built my own.
>ajustable from 0-60sec to delay switch on
>wile the pc boots so my relays dont flicker.
>no 555 timer in this circuit.
>just a large cap to do the timeing.
>i could send a circuit to youre
>email if you want it.

---
Why not post a copy to alt.binaries.schematics.electronic so we can
all enjoy it?

And, BTW, don't top post.

--
John Fields
Professional Circuit Designer

how do you attach the photos?

i will do it soon.

"John Fields" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Thu, 6 Apr 2006 18:57:02 +1000, "crazy frog"
> <(E-Mail Removed)> wrote:
>
> >ive had the same prob needing a 30second to 60
> >for a automation project, so built my own.
> >ajustable from 0-60sec to delay switch on
> >wile the pc boots so my relays dont flicker.
> >no 555 timer in this circuit.
> >just a large cap to do the timeing.
> >i could send a circuit to youre
> >email if you want it.
>
> ---
> Why not post a copy to alt.binaries.schematics.electronic so we can
> all enjoy it?
>
> And, BTW, don't top post.
>
> --
> John Fields
> Professional Circuit Designer