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Need a 555 cct that can only be triggered once during its countdown time

davenn

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Sep 5, 2009
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That is, once the 555 timer has been triggered, it cannot be triggered again till countdown has ended

problem ....
Doorbell gets constantly pushed by little clowns passing by the house
What it so that once the button is pushed, the 555 is triggered and the doorbell does its single ding dong
and no matter how often the button is pushed the doorbell wont get activated again till the timer counts down
say something around 20 - 30 sec

The 555 output will be triggering a relay that operates an AC bell
have done a massive hunt through dozens of timer ccts without seeing something for this purpose
if it takes 2 x 555's or a 555 and something else, no prob.

just showing up my lack of design abilities ;)

cheers
Dave
 

Kiwi

Jan 28, 2013
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G'day Dave, hope the health is improving.

My suggestion would be to disconnect the push button from the doorbell circuit during the count down, and connect it to a car windscreen washer pump. That way if the button was pressed they would get a squirt of water. :D
 

Anon_LG

Jun 24, 2014
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The switch could activate a second 555 timer in monostable mode, set it so that the pulse lasts the 20-30 seconds when activated, feed the output to a NOT gate, which feeds into a transistor, cutting the switch from the doorbell temporarily, when the pulse ends the switch will work again, enabling another press and wait.

I hope your health is improving,
 

davenn

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The switch could activate a second 555 timer in monostable mode, set it so that the pulse lasts the 20-30 seconds when activated, feed the output to a NOT gate, which feeds into a transistor, cutting the switch from the doorbell temporarily, when the pulse ends the switch will work again, enabling another press and wait.

I hope your health is improving,

Im out of hospital, but not any better, after all the tests, they have no idea what is causing all the probs :(

any chance in putting a possible schematic together for me please .... Im in service, not design LOL

cheers
Dave
 

Anon_LG

Jun 24, 2014
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I am sorry to hear that Dave, still, I hope it improves.

I have attached what I think the circuit should look like. The control values I have provided will give a delay of about 22 seconds, which as a teenager myself, I know I could not stay patient that long. The 555 output feeds back to de-activate the switch for this time period after being pressed, upon the 555 output going low again the switch is re-activated. The 5 volt supply can be any voltage up to the 555 timer's maximum rating. The non-inverted 555 output can be fed into the base of another transistor to activate the existing circuitry.

This is as non-convoluted as I can make the circuit. Good luck trying to understand my bad circuitry. I am happy to continue providing advice on how I think the circuitry should work.

I hope this helps,
 

Attachments

  • Circuit_to_stop_the_chavs_from_spamming_Dave's_bell.zip
    9.2 KB · Views: 94

Arouse1973

Adam
Dec 18, 2013
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Hi Dave, here's my attempt if your interested. It sounds like it's similar to Lavaguava's but I don't know what package he used to design it in, might be better if he posted a picture. You may have to play around with the values for timings.

Circuit works like this. When the door button is pressed C5 charges up via R5 and T3 and T1 turn on after a short delay. The relay energises and one contact triggers the 555 and the other which I have left blank controls your bell. The 555 output goes high and after a short delay T2 turns on disabling any further presses of the door switch until the output of the 555 goes low. The RC for T2 is to insure the bell has time to DING DONG! before it is disabled. The other RC, R5 and C5 ensure the transistors have long enough to turn the relay on for the bell to operate. I have chosen a Darlington arrangement for two reasons, Some extra gain for driving the relay and also when T2 switches on it ensures that T3 and T1 are fully off.
Thanks
Adam

555_DB.PNG
 

davenn

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Thanks guys
really appreciate that :)

when feeling well enough will have a play knocking the circuits up on breadboard and see how it goes

I am sorry to hear that Dave, still, I hope it improves.

I have attached what I think the circuit should look like.

thanks :)
what do I open a .sch file with ?

cheers
Dave
 

Anon_LG

Jun 24, 2014
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Oh yes sorry, I generally draw schematics in EAGLE CAD, the file is a zipped EAGLE schematic file.

There is little point opening mine now however, as Adam has shown me up with his full schematic. :D
 

Arouse1973

Adam
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Oh yes sorry, I generally draw schematics in EAGLE CAD, the file is a zipped EAGLE schematic file.

There is little point opening mine now however, as Adam has shown me up with his full schematic. :D

It's good to have everyone join in, please upload a picture of yours.
Thanks
Adam
 

Arouse1973

Adam
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That's very good, now add the other bits :) Don't copy mine, see what you come up with. Although it may be the same. It's interesting to see how other people design circuits.
Adam
 

Anon_LG

Jun 24, 2014
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OK, I have added what I think the full circuit should look like. Note that there is no AC supply to the buzzer, the symbol SG1 is meant to represent both the AC supply and the buzzer.

The deactivation 555 timer output is inverted then fed into the activation 555 timer. The output is inverted before feeding into the activation timer as 555 timers are falling edge triggered, the inverter causes the rising edge of the deactivation pulse to become the falling edge, therefore activating the ding when the switch is pressed, rather than 22 seconds later, as it would without the inverter.
Circuit_to_stop_trolls_spamming_Dave's_bell.jpg

That is my version. T2 and T3 should be transistors that can handle the power involved when switching the relay, I merely chose TIP31 arbitrarily. There should probably also be a flyback diode across the solenoid (K1), however I have rarely work with inductive loads and so can provide little advice on this matter.

Hope this helps,
 

Arouse1973

Adam
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That's good, yes and a flyback diode is needed, especially as you are driving the relay from a common collector drive. The only other thing I would say is the output voltage from the 555 at 5 Volts will be further reduced due to the Vbe drops of the two transistors. You may find it difficult to find a relay that works at this low a voltage, but I haven't really looked so it's just and observation.
Adam
 

Anon_LG

Jun 24, 2014
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That is impressive analysis Adam. I did not factor in the Vbe drops, I assumed that the supply voltage was higher, something around 9-12 volts, can you confirm this Dave?

It appears that there are relays available that switch at 5 volts though I am unsure whether they can carry the required power levels. Again, it depends on what Dave has, he may already have the relay designed to work with the supply voltage.
 

davenn

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yes the DC voltage available will be higher, up to 10 - 12V if needed

appreciate your efforts :)
 

Colin Mitchell

Aug 31, 2014
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" but Dave wanted to use a 555 timer."
There is no point in using a 555 when it is not needed.
"your circuit will require a small delay so the bell is on for long enough initially."
That is NOT how a ding dong bell works.
 

Arouse1973

Adam
Dec 18, 2013
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" but Dave wanted to use a 555 timer."
There is no point in using a 555 when it is not needed.
"your circuit will require a small delay so the bell is on for long enough initially."
That is NOT how a ding dong bell works.

Please explain how they work.
Adam
 
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