Simple delay circuit

ive found this circuit:

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

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

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

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

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

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

Good luck with your project Chris

--- 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:

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:

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.

how do you attach the photos?

i will do it soon.

the circuit is in alt.binaries.schematics.electronics now

John, one or two lines at the top of a message is obviously the most convienient way to communicate (don't come back with BS of keeping post order, you're smart enough to sort out the quote levels and 99% of posts get through these days).

Or better still, a couple lines below a couple lines of quoted text, as here. Even you, dear John, have failed this, placing in fact three levels of quoted text, totalling a whole 27 lines, above your mere four lines of response. I dare say you have no room to complain.

Tim

how can it suck, if it f***in works. i made it work the way i wont it to work. dick head

thankyou for backing me up tim

get

Plonk.

-- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85.

Michael A. Terrell Central Florida

Wow, I guess you really told him! Now, lets see what you accomplished with that reply:

Etc.

Ouch!