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Time delay circuit

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firealarmfreak

New Member
Hey, I am making my own homemade fire alarm control panel, because i love electronics and fire alarms.

I have a 160 in one elecronics project kit and i have a relay which creates a latching circuit.

But now i want to create a delay circuit so that when i pull the alarm it waites 1-3 seconds before the alarm goes off.

I have 3 pull stations, 1 bell and 1 strobe connected to the board.

I do not have access to the 555 timer or any intergreated circuits (Yet) but i herd i could just use resisters and capaciters.

Anybody know how to do this, some instructions would be greatly appreciated.

Feel free to contact me through e-mail at: firealarmfreak@gmail.com

Thanks.

Chris.
 

firealarmfreak

New Member
Time delay circuit question

Hey, I am making my own homemade fire alarm control panel, because i love electronics and fire alarms.

I have a 160 in one elecronics project kit and i have a relay which creates a latching circuit.

But now i want to create a delay circuit so that when i pull the alarm it waites 1-3 seconds before the alarm goes off.

I have 3 pull stations, 1 bell and 1 strobe connected to the board.

I do not have access to the 555 timer or any intergreated circuits (Yet) but i herd i could just use resisters and capaciters.

Anybody know how to do this, some instructions would be greatly appreciated.

Thanks.

Chris.
 

rjvh

New Member
wy would you delay a fire alarm signal :confused:
peoples life are in danger

according the NFPA it is not aloud to delay an alarm triger signal from a manual pull station

Robert-Jan
 

firealarmfreak

New Member
RE: Delay cicuit question

I don't understand it either.

But in a real fire alarm system they have a delay because at my middle school they gave me permission to pull it to test it (they called the fire dept ahead of time to tell them not to come) and there was a 3 second delay before alarm actiavtion so to learn electronics i thought it would be cool to put in that feature on my homemade panel since my panel is not for real emegergency use.

anybody no how to do it wityhout any intergreated circuit?

Chris.
 

rjvh

New Member
it is posible that the alarm sound delayd but so far i know this is not done intentional
and you should not build it in your system
in case of an emergency every second counts

in sprinkler systems there could be alarm trigering delays build in but that is done for a different reason
and these delay systems are build mechanicaly (never seen an electronic one)

it's nice to experiment with this idea but keep in mind that failing of a system like this can have big consequenses and i would warn you if you gona use this system
if you have nothing now this is always better but don't sell it
Robert-Jan
 

shaneshane1

New Member
firealarmfreak said:
Hey, I am making my own homemade fire alarm control panel, because i love electronics and fire alarms.

I have a 160 in one elecronics project kit and i have a relay which creates a latching circuit.

But now i want to create a delay circuit so that when i pull the alarm it waites 1-3 seconds before the alarm goes off.

I have 3 pull stations, 1 bell and 1 strobe connected to the board.

I do not have access to the 555 timer or any intergreated circuits (Yet) but i herd i could just use resisters and capaciters.

Anybody know how to do this, some instructions would be greatly appreciated.

Thanks.

Chris.


i suppose you could use a resistor with a capacitor, and when it slowly gets to a certain voltage it would trigger the alarm, but the only way i know how to do that is to use a voltage camparitor, but thats a IC and thats no good for you is it?
 

Boncuk

New Member
Time delay

Hi firealarmfreak,

here is a very simple delay circuit just using one transistor.

You can use any small signal NPN-transistor for the circuit. R1 restricts the charge current of C1. If the threshold voltage exceeds 0.7V the transistor will conduct and the LED is lit. R2 takes care of discharging C1.

With the values given in the example the delay time is approximately 3 seconds.

Just keep in mind that delaying a fire alarm signal there might be fatal consequences.

Regards

Boncuk
 
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Hero999

Banned
A 555 is really the only way to do it, you can use a couple of transistors but it won't be very stable.
 

Boncuk

New Member
Hero999 said:
A 555 is really the only way to do it, you can use a couple of transistors but it won't be very stable.

Hi Hero,

A 555 isn't a high precision timer either, but takes more wiring. Precision only depends on the quality of Rs and Cs.

All he wants is delaying the alarm output for a period. I think it doesn't make a big difference if this delay is 3 seconds or 4.

A real precision timer requires a crystal oscillator, and even that might not be accurate enough due to crystal tolerances and frequency drift with changing temperatures.

Simulating any circuit ageing of parts is never taken into consideration and therefore a simulation will always be perfect with absolutely no tolerances.

Regards

Hans
 

rjvh

New Member
I still have a small problem that he want to use it as a delay for a fire alarm trigering
i do also understand that he see it from an educational point of view but still than, alarm systems are there to warn people for danger and you should not delay that.

in my preveous job (M&E coordinator/inspector) i did deal a lot with fire alarm and i still do a lot with fire fighting systems if you read the codes this is something that you have to discurage (i mean the delayed trigering)

Robert-Jan
 

Andy1845c

Active Member
I can't think of any practical reason to add a delay in an alarm either. I suppose a delay would give you time to reset a alarm switch if it was bumped or pulled mistakenly, but this isn't practical. Most alarm switches I have seen (I actully have a few somplace) can't be reset without opening the switch with a special screw driver. The older ones had a glass rod that would break when you pulled the leaver down.

I'd suggest that firealarmfreak research reason behind the delay. If your doing this for a school project, I bet your local fire marshall would be willing to tell you about why it happens and if its done intentonally.
 

kchriste

New Member
Forum Supporter
The delay probably has more to do with the systems antifalsing circuitry than anything else. The alarm probably needs for the signal from the pull switch to to valid for a short period of time before it trips the bells and notifies the fire dept.
 

silvarblade

Member
i do agree with the person above(sorry forgot to remember his name) you can use a RC circuit for your delay time. its easy but not always reliable!!
 

slosjo

New Member
@firealarmfreak-
Reguardless of what you are using a delay for, this website does a good job of explaining how a RC timer circuit works.

https://www.electronics-tutorials.ws/rc/rc_1.html

You have to carefully select the values of R and C to get the desired delay, and if you are looking for 3 seconds, you will need a big cap. The best thing to do would be to connect the output of the circuit on the above webpage across the contacts of something with a threshold voltage, e.g. a relay, transistor, etc...or something else that will turn on only when the voltage gets to a certain point to activate your alarm or whatever it is you are trying to turn on.

There are better ways to accomplish what you are trying to do with integraged circuits, but this is the quick and dirty "RC only" solution.

-slosjo
 

firealarmfreak

New Member
Hey everybody that says they dont know why i want to delay a fire alarm signal and how its unsafe.

I am NOT using this panel as a real emegergency device. Its for my own experience and enjoyment. we have smoke alarms that dont delay in our house.

All i want is one simple explanation, dont worry this is not to be used for any real emergency.
 

firealarmfreak

New Member
Hey I found out what the delay is for, Its for verification. When you pull the alarm, the panel waits 1-3 seconds to verify that the pull station is still activated, if not, the panel is sent back to normal, if so, the panel goes into alarm.
 

rezer

New Member
Fire/Burg alarm systems will often have programmable delays for zone activation. This is to cut down on false calls. They sometimes will use cross-zoning as well, in that two zones within the same area must be active before an alarm is considered valid. But this is primarily for the burg alarms. Still the delays exist because alarm companies are charged fees if police or security respond to a false alarm.

Are you using a pull-station?

If so, you can use a series RC circuit like what has already been suggested. What type of input will this be going to?
 

oz93666

New Member
here's how to do it with one cap (5000uF) and one resistor (100 ohm 1w)......solder the cap across the coil terminals of the relay. The -ve terminal of cap is connected to -ve battery, the +ve terminal of battery connects through the resister to +ve end of cap. As power flows through the resister the cap will gobble it up preventing the relay from pulling , the voltage rises across the cap to the point where the relay pulls. Above values give about 3sec delay with a very small sensitive 9v.relay. With larger relay you will have to decrease resister value and increase cap value......
 
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killivolt

Well-Known Member
here's how to do it with one cap (5000uF) and one resistor (100 ohm 1w)......solder the cap across the coil terminals of the relay. The -ve terminal of cap is connected to -ve battery, the +ve terminal of battery connects through the resister to +ve end of cap. As power flows through the resister the cap will gobble it up preventing the relay from pulling , the voltage rises across the cap to the point where the relay pulls. Above values give about 3sec delay with a very small sensitive 9v.relay. With larger relay you will have to decrease resister value and increase cap value......

This post is from "2008"
 

oz93666

New Member
This post is from "2008"

I first found this site last week when I Google searched 'simple time delay circuit' , we must remember that this site is an enormous resource of expanding information which thousands of unseen information seekers , who never join or post , may be drawn to . It was them as well as the posters I was addressing..
 
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