A real easy one for you clever guys, Ive seen loads of tripwire or laser alarms circuits on the internet using a 555, that will pulse and output for say 30 seconds but I need one that will automatically reset itself after a set time/output ready for the next trigger, is this poss ?

Thanks

 

Yes, use it in the monostable mode, using the capacitor trigger method, .

What is your requirement.?

 

By "pulse" do you mean to output a continuous pulse chain?

For that you would use one 555 set up as a monostable connected to the reset pin of another 555 in astable mode.

A 556 is ideal for this.

 

Its going to be a trip wire alarm thats running off a constantly trickle charging 12v vehicle battery, the voltage can be regulated to 5v.
The idea is fishing line connected to some type of momentary switch, triggered the system will pulse a relay, the relay will be powering strobe and horn, beeep----beeep----beeep----beeep for 15, 20, or 30 seconds then automatically resets itself ready for the next trigger, is this poss?

 

Yes with the circuit I posted, using the monostable mode, I take it the trip switch will reset itself.

 

Yes with the circuit I posted, using the monostable mode, I take it the trip switch will reset itself.

Thanks,

so s1 is to arm the system,
what sort of switch would I use for s2
how would I adjust the output time before the system resets
can a relay be placed where led1 is

sorry for all the questions
Thanks Again

 

This is the way I would use it, to alter the relay time adjust R1 and C1 to give you the desired time,



for 10 seconds R1 is 100k and C1 is 100uF,
15 seconds is R1 150K and C1 100uF
30 seconds is R1 300K and C1 100uF
Time is set by the formula T= RxCx1.1 seconds

R is in ohms and C is in Farads

https://www.allaboutcircuits.com/tools/555-timer-monostable-circuit/

 

Thanks

Is there any way of having the trigger on a delay, say 10 seconds, time to disarm or switch the unit off?

 

Thanks

Is there any way of having the trigger on a delay, say 10 seconds, time to disarm or switch the unit off?

Sure, just use 2 timers in a cascaded configuration...then use a toggle switch to pull both resets low before the first one times out.

 

Sure, just use 2 timers in a cascaded configuration...then use a toggle switch to pull both resets low before the first one times out.

Thanks, being thick that has gone over my head, could you give me a little more info please on this

 

Ok, give me some time and I'll get you a schematic.

 

The NE555 can drive up to 200mA.
So I don't think the 2N2222 is really needed in the circuit of post #7

 

Here ya go.

The top trace is showing a reset before the second timer triggers. (about in the middle of the 10 second time)
The middle trace shows the second timer output without reset. (about 30 seconds before auto reset)
The bottom trace shows the reset pulse from the toggle switch.

Don't be confused by the electronic switches used in the sim, your trigger will be whatever you use as the trip wire (must pull timer trigger low) and the toggle switch is just that an ordinary toggle switch.

If you use a momentary toggle switch just engage for about half second.

I didn't show any of your connections to the relay, just the coil and flyback diode.

Timer 2 must be a bi-polar type to avoid using a transistor. (IE: NE555)

In this configuration you could add a "pre-alarm" buzzer on timer 1. (many professional systems come with a pre-alarm buzzer.)

D1 and D2 may not be needed but I'm not going to get into that debate.

 

Thanks, trigger is going to be a N.O reed switch, the arm / disarm will be a key switch or combination pad if I can get a reasonable priced jobby,

yes I would like to add a pre alarm buzzer, where would this connect to, last question (for today anyway) could a potentiometer be used to adjust the delay time?

Thanks Again

 

A pre-alarm buzzer would connect to timer1s output to ground. (negative) May need some adjustment of the coupling cap.

Yes, a "pot" configured as a variable resistor can be used to adjust the time on both of the timers. (just be sure to place a fixed resistor in series with it to avoid bad things.)

Be sure to use twisted pair from the reed switch to the trigger or perhaps shielded cable to avoid false triggering.

 

Thanks, trigger is going to be a N.O reed switch,

Does this trip wire reset itself or do you have to manually?

 

Thanks for the "Like" but that didn't answer my question.

 

Does this trip wire reset itself or do you have to manually?

manually, as the door on the unit could be open for a while so that would make the reed switch closed, I think the trip wire will be at the back of the unit pulley'ed up to a momentary switch that wont get touched until its tripped (over)

So the idea is, open main door (reed switch closes) triggers the timer, that gives me time to key in code or switch off key switch to disarm the system, when leaving arm the system, close the main door and leave........

Just had a though, when arming does that also give me a delay ?

 

Just had a though, when arming does that also give me a delay ?

Not currently and don't you want the output from the timer to pulse the relay?

 

Not currently and don't you want the output from the timer to pulse the relay?

Ahhhhhh, back to the drawing board then, as yes I would like a delayed arm and also, yes the relay needs to be pulsed as that will be switching horns on a like old car alarm