Time d..............elay circuit.

[shockz]

Hi guys. i have a task for you guys to tackle. Im wanting to contruct a circuit that incorporates 1) an alarm 2) time delay 3) electronic lock.

First of all i want to be able to incorpate a time delay of about 10 seconds in which the alarm would then trigger . In accomplishing the design for the delay circuit i would like to be able to reset the circuit within this 10 second delay using some sort of electronic lock. I would be very gratefull on your commments and any prototypes of any part of this circuit or all stages of the circuit.

The alarm in which i would like to incorporate these features is based on a LDR circuit that i have. it is very sensitive and triggers as soon as light hits is. However, I would also like to incorpate the feautes into a lazerbeam circuit that i also have.

 

[ericgibbs]

Hi guys. i have a task for you guys to tackle. Im wanting to contruct a circuit that incorporates 1) an alarm 2) time delay 3) electronic lock.

First of all i want to be able to incorpate a time delay of about 10 seconds in which the alarm would then trigger . In accomplishing the design for the delay circuit i would like to be able to reset the circuit within this 10 second delay using some sort of electronic lock. I would be very gratefull on your commments and any prototypes of any part of this circuit or all stages of the circuit.

The alarm in which i would like to incorporate these features is based on a LDR circuit that i have. it is very sensitive and triggers as soon as light hits is. However, I would also like to incorpate the feautes into a lazerbeam circuit that i also have.

hi,
From your description I guess you are asking for an 'entry & exit' delay for the alarm system.

The detectors either LDR/laser would be triggered when the beam is broken and an alarm delay circuit activated, after this delay period, unless its cancelled using the 'electronic lock', the alarm wound sound.

What type of alarms do you want to control also what do you mean by electronic lock.?

 

[shockz]

well i have two designs. the first is a ldr alarm that i have placed in a box, when the lid is removed it sounds. i have this circuit up and running. it works fine however, it is impractical as when i open the box it sounds straightaway and obviously i dont want it to sound on my entry only on intuders so i need a delay in which i can reset it. the second alarm is to secure a room using an infrared transistor and a laser. when the laser breaks i want a delay so that i can reset the alarm.

what i mean by an electronic lock is a means to disable the alarm using a keypad or switches etc.

 

[ericgibbs]

well i have two designs. the first is a ldr alarm that i have placed in a box, when the lid is removed it sounds. i have this circuit up and running. it works fine however, it is impractical as when i open the box it sounds straightaway and obviously i dont want it to sound on my entry only on intuders so i need a delay in which i can reset it. the second alarm is to secure a room using an infrared transistor and a laser. when the laser breaks i want a delay so that i can reset the alarm.

what i mean by an electronic lock is a means to disable the alarm using a keypad or switches etc.

hi,
Do you have any 555 timers and transistors/components already on the shelf for this delay.
If you fill in your location we can advise where to get the bits you need if you dont already have them.

 

[shockz]

i have a load of components ranging from 555 timers, 556, resistors caps, thermistors, transitors, lazers, optocoupler etc. im just unsure if how to incorpoate the delay into my circuit and how to build a keypad in there aswell

 

[ericgibbs]

i have a load of components ranging from 555 timers, 556, resistors caps, thermistors, transitors, lazers, optocoupler etc. im just unsure if how to incorpoate the delay into my circuit and how to build a keypad in there aswell

The option I would choose is to configure a 555 as a monostable.
This would be triggered by a break in the 'beam', the monostable timing period would inhibit the alarm from sounding during the delay.
At the end of the delay the monostable restting would set an alarm latch so that the alarm would sounds continuously, until you stop it.

If during the delay you cancel/inhibit the alarm latch by using a switch etc, the alarm would not sound.

I would use a 2nd 555 to do the same thing for an 'exit' delay.
You would switch on the alarm enable which would start the 555 mono, which would inhibit the 1st mono from being triggered while the exit delay is running.

Post a diagram of what you have already got installed.

 

[shockz]

https://www.electro-tech-online.com/members/shockz-albums-shockz-picture41214-working-alarm.html

 

[shockz]

this is the circuit that im using,however, instead of the variable im just using 2x 2.2k resistors. it works fine. just how i want it to.

 

[ericgibbs]

hi,
If you want to keep the LDR as the beam detector I would replace the siren with a fixed resistor and add a 2nd transistor.
The low going output of the 2nd transistor would trigger the 555 timer, at the end of the entry time delay, a latch would be set which sounds the siren.

 

[shockz]

hmmm, so would i keep the 47micro farad capacitor in there? and are you suggestin that i only use one 555 (monostable) timer. where would i insert this latch?

 

[ericgibbs]

hmmm, so would i keep the 47micro farad capacitor in there? and are you suggestin that i only use one 555 (monostable) timer. where would i insert this latch?

hi,
I can only see 1uF cap across the siren, that would stay with the siren.

The 555 is for the 'entry' delay.
This latch could be a logic latch or a relay type latch, which would go after the 'entry' delay 555 timer.

An 'exit' timer would inhibit the LDR transistor from triggering the system.

Are you asking for a circuit diagram or would you prefer to design your own circuit.?

 

[shockz]

just so that i can understand the circuit a little more, a diagram would be very useful. i can then experiment myself. if that is ok?

 

[ericgibbs]

just so that i can understand the circuit a little more, a diagram would be very useful. i can then experiment myself. if that is ok?

ok,
If no one else posts a circuit today, I'll post one Tuesday.

Using the 555's you have on the shelf is the cheapest way to go.

 

[shockz]

ok, thankyou very much, i apreciate that.

 

[ericgibbs]

ok, thankyou very much, i apreciate that.

hi,
This is a working version of the entry/exit timer for the IR/LDR beam break.
Breaking the beam would set a latch and trigger an entry 555 monostable.
If at the end of the timing period you have not RESET the system the alarm will sound until you reset it.

When you want to exit thru the beam, press the RESET this will trigger an exit 555 mono, at the end of the exit period delay the system will become active.

If this looks OK for your app, let me know and I will tidy up the drawing.

I need a couple of measurements from you, the voltage across the LDR when the beam is broken and not broken.
Also details of the siren, working voltage and resistance.

EDIT:
The left side of the plot shows an exit cycle and the right side an entry with alarm, which you reset.

 

[shockz]

ive since revised the circuit that i sent you and it doesnt work under the conditions that i want it to, for some strange reason. this is another circuit that i have made... its very sensitive to light.

 

[ericgibbs]

ive since revised the circuit that i sent you and it doesnt work under the conditions that i want it to, for some strange reason. this is another circuit that i have made... its very sensitive to light.

hi,
That original circuit that you posted the link for, would never work.
Do you have a link to the thread where you found it,?

Post diagrams of the circuits you are working on.

 

[mbarazeen]

what about the lock you mentioned?? you have one already? or willing to make one digital lock by your self?

 

[shockz]

i want to make to reset the alarm. so basically before the alarm goes off there is a delay in whihc i can stop the alarm by sounding. i want to use a comination lock of some sort to do this. any ideas?

 

[shockz]

**broken link removed**

the first circuit responds to light. the second to shadows. these are the basic circuits i have developed. with the addition of capacitors as shown. ive been able to add a very short delay before the alarm sounds and allow the alarm to trigger fora further 10 seconds when light is removed.