What component is needed here?

[fullyBoricua]

Hello there! 

I'm trying to figure out what electronic component should I use so the BUZZER will only sound for 1 second when the switch is pressed for an indeterminate period of time. If the switch is pressed less than 1 seconds, it doesn't really matter if the buzzer sounds or not.



Edit:
- I have no control over the 12v line, I need to solve this with GND

Any pointers will be appreciated, thanks!

[Simon]

You could do it with a 555 timer but you need to be more certain of what you want. If the functionality you are after of complex a micro controller could be used.

[DTJ]

Fancy and neat or quick and dirty?


Depending on the sensitivity of the buzzer, try an electrolytic cap with a diode across it to discharge the cap when the button is released.

[fullyBoricua]

@Simon, I tough about it but I was hopping for a simpler solution. Guess that will be plan B.

@DTJ The buzzer is very beefy (3 - 24v) and quick and dirty sounds about right 
But I fail to understand how to make this work as you suggested... the CAP will be feeding the buzzer constantly after charged and I just want the opposite.

Thanks again!

[PA0PBZ]

But I fail to understand how to make this work as you suggested... the CAP will be feeding the buzzer constantly after charged and I just want the opposite.

You put the cap in series with the buzzer, so when the cap is charged there will be no more current flowing.
However, to discharge the cap the diode has to conduct and the cap will never charge more than the diode drop... hmm

[fullyBoricua]

I did a quick test with a SMD 6.3v cap in series with the buzzer on a breadboard... the buzzer is still on after even 12v of applied voltage.
I really don't understand how to make this work as suggested...

Guess I'll go with the 555 solution, I feel much more comfortable with ICs.

Thank you all guys!

[tatus1969]

do you have access to the 12v rail for your circuit? if no, it will be tricky to find a solution.

[fullyBoricua]

I do, but the "switch" must stay in ground.

[Tandy]

Sounds like you want a Monostable circuit to produce a single output pulse when it is triggered. There are many ways you could do it with transistors or something like a 555 timer. You can then set the duration of the on time using a potentiometer (variable resistor) if you like.  Here is a transistor based example http://www.learningaboutelectronics.com/Articles/Monostable-multivibrator-circuit-with-transistors.php

[fullyBoricua]

@Tandy, that is exactly what I want! I didn't know the name and I guess that's why I failed searching google to get an answer for this problem.

I know it was a good idea to ask here  As I got 2 solid options now.

I need about 200 of these, so I guess I'll go for whatever is easier to implement.

[Zero999]

Sounds like you want a Monostable circuit to produce a single output pulse when it is triggered. There are many ways you could do it with transistors or something like a 555 timer. You can then set the duration of the on time using a potentiometer (variable resistor) if you like.  Here is a transistor based example http://www.learningaboutelectronics.com/Articles/Monostable-multivibrator-circuit-with-transistors.php

And if one of the transistors is replaced with a MOSFET, the quiescent current draw and be minimised.


t = 0.7*R1*R3

[Audioguru]

None of the transistors or ICs I have seen have datasheets listing their absolute maximum output current as "Beefy". Instead they all say the maximum current in mA or Amps.
The buzzer on a fire truck draws about 20A and it is "Beefy". A power Mosfet can drive it.
How much current does your buzzer draw??

[fullyBoricua]

@Tandy, looking at the monostable diagram closely, I noticed that the pulse (switch) must be initiated from V+, but I only have access to V-, or in other words, I can only generate my initiating pulse from ground as showed in my first drawing.

@Audioguru 8mA @ 12v. Sorry about the "beefy" term, I tried to imply that the buzzer was not gonna blow by a voltage spike.

[Zero999]

@Audioguru 8mA @ 12v. Sorry about the "beefy" term, I tried to imply that the buzzer was not gonna blow by a voltage spike.

Then a small BJT or 2N7000 will drive it easily.

Going by what you've said, it's probably a piezo buzzer, which doesn't produce a high voltage back-EMF pulse, so D2 on the schematic I posted isn't necessary.

D1 is there because the maximum reverse voltage of a transistor's base is typically 5V and the circuit is run from a 12V supply. When Tr1 turns on, the voltage at D1's anode will be -(12-two diode drops) or approximately -(12 - 2*0.6) = -10.8V.

[Cerebus]

I do, but the "switch" must stay in ground.

Lets try to be absolutely clear here. You can do this, yes?

[fullyBoricua]

@Hero999 Thanks Hero.

Yes it a piezo buzzer. I'm looking at your diagram and as you already have probably guesses, I'm no expert in this.
I think I can replicate it on a breadboard.

In my initial diagram I draw a switch, in the real application I'm controlling a board output (much like a GPIO from a Raspberry) and sending ground via that PIN. That's my real switch. I'm mentioning this because, maybe, there's a simpler way to do this knowing that info.

This ground output will be only activated in 2 ways:
- For a 10 secs period
- For an indeterminate amount of time > 10 secs (for example 3 hours)

And for both cases, I only want the buzzer to sound for 1 second.

Thanks and sorry if I explained this poorly!

[fullyBoricua]

@Cerberus No I can't.

In the real application I'm controlling a board output (much like a GPIO from a Raspberry) and sending ground via that PIN. That's my real switch.

[Zero999]

@Hero999 Thanks Hero.

Yes it a piezo buzzer. I'm looking at your diagram and as you already have probably guesses, I'm no expert in this.
I think I can replicate it on a breadboard.

In my initial diagram I draw a switch, in the real application I'm controlling a board output (much like a GPIO from a Raspberry) and sending ground via that PIN. That's my real switch. I'm mentioning this because, maybe, there's a simpler way to do this knowing that info.

This ground output will be only activated in 2 ways:
- For a 10 secs period
- For an indeterminate amount of time > 10 secs (for example 3 hours)

And for both cases, I only want the buzzer to sound for 1 second.

Thanks and sorry if I explained this poorly!

Well the circuit I posted needs an independent power supply so it seems like it won't do that in its current form.

It can be done with two wires. I'll draw the circuit later, if someone else doesn't beat me to it; I'm going out soon.

If you're using a Pi then why not simply do the delay in software?

[Cerebus]

@Cerberus No I can't.

In the real application I'm controlling a board output (much like a GPIO from a Raspberry) and sending ground via that PIN. That's my real switch.

But you still have access to ground, the switch output (really a GPIO/whatever), the 12V rail and the ground/return from the buzzer?

[NottheDan]

But you still have access to ground, the switch output (really a GPIO/whatever), the 12V rail and the ground/return from the buzzer?

For what I understand what he is trying to say is that he has only access to the ground wire coming from the buzzer, not the buzzer itself, not the feed to the buzzer, not the controller and not the 12V rail. Just that one wire.

So he wants a circuit that cuts out one second after going high, stays so until the line goes low again and resets then.

But I might be wrong.

[fullyBoricua]

I'll try to explain again, this time including all the details.
Thanks beforehand for all your patience.

I have a GPS Tracker mounted on a car:


We are interested in PIN6, this PIN is a general output that, when triggered, will produce GND (or V-, I really don't know the correct terminology in this case). This PIN is used to control a relay (140mA), so I can "leech" from it and if I keep the leech under 160mA everything should be Ok.

The trigger is caused by an external factor, I don't control it, and it's not important. What's important is that the "length" of the pulse will be either:
- A 10 seconds pulse
- A >10 seconds pulse (can be minutes, or hours)

So I have this buzzer from ebay http://www.ebay.com/itm/172190049345?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT and all I want to do is, the instant that the trigger fires, sound a buzzer  for about 1 second.

What I do have:
- I can wire 12v and GND from the car
- I can wire the buzzer as I want
- Access to PIN6

Thanks again!

[kxenos]

You can try a PTC

[fullyBoricua]

@kxenos certainly worth a try, I will need to order very small ones and try them out

Edit: The smallest PTC in digkey it's 14mA for trip... so it won't cut it. I just re-tested the buzzer with the power supply bench and it's 5mA @ 12v

[Tandy]

So I think you are basically saying that when the source is triggered the pin 6 on your box is connected to ground (pulled low).

If you use the inverting input on a 555 timer that will trigger on the low signal if you keep it held high with a high value resistor.

[Tandy]

Done a search for you for a 555 inverting monostable circuit and found this article that may help http://www.learnabout-electronics.org/Oscillators/osc45.php