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CRE

Puggy Potty Alarm

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Nope, no joke, one of my pugs is getting out of hand with his "marking" behavior..... It's driving us nuts. So, I plan on placing some alarm in every area he's "tagging". I've got bare copper tape (used in stained glass work) which I'll run in two horizontal lines with only about a millimeter gap.

The part I'm having trouble with is the audible alarm. I'd like to build a piezo driver which'll push about 80-90 dB. I'm going to use a 555 monostable to only allow the sirem to scream for a few second when triggered, then reset.

Anyone have a schematic for a good loud piezo driver? I've got a few different piezo transducers on hand but I'll probably use the larger ones I picked up at RatShack (273-073A).

Thanks!

Edit: One more thing, I do want this circuit to run at an audible frequency, so I know when something's been done. Also, the electric dog whistles I've found are too quiet.... any idea how make a louder version:  http://www.zen22142.zen.co.uk/Circuits/Misc/whistle.htm That's one I've tried.

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Hi CRE,
Sure it's a joke!  ;D ;D
If you drive the piezo transducer with a bridged audio amp like an MC34119, it will have 4 times the power. It will be so loud that your pug will stop what it is doing in mid-stream and be afraid to "mark" again.
I used an MC34119 in my son's alarm clock and it can be heard down the street.
You will also get a lot more performance from a battery powered circuit if you add a bypass cap across the battery connections on the pcb, maybe 100uF.

Those piezo thingy's are much louder when they are mounted in a small jar or something that resonates at their frequency. Many are made mounted in the back of a plastic housing that is their resonant cavity. Since the piezo and its cavity are resonant, you must tune the oscillator's frequency for the best, loudest match.

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Guest Alun

Try this circuit you could use a 7555 for low power of a 556 dual timer to save space/money or a 7556 to get the best of both.

To achive a very large amount of power use a bridge op-amp driving a 8ohm to 1K audio transformer with the input on the 8ohm and piezo on the 1K secondary.

But be warned these circuits can damage your hearing and the audio transformer idea may destroy a piezo element if the output voltage is too high.

post-0-14279142168644_thumb.png

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Hi Alun,
He, he. Silly you again!
[move] ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  :o :o :o  :o :o :o  :o :o :o  :o :o :o  :o :o :o  :o :o :o  :o :o :o  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  :o :o :o  :o :o :o  :o :o :o  :o :o :o  :o :o :o  :o :o :o  :o :o :o[/move]

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Hey guys, thanks for all the responses.

For the time being I've set up a small analog buzzer from RatShack which made for some VERY amusing moments last night.... so funny, so sad.... poor startled little doggy..... so funny!I think I'll give Alun's circuit a shot, but I was wondering if I could substitute the CA3130 with another op amp such as a LM740 or a LM1458? These I have on hand.  :D

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Hi CRE,
Did your startled little pug stop mid-stream?
You can use any opamp for Alun's corrected circuit, but you didn't notice the elbow that I gave him. His latest circuit must be trying to save battery power because the opamp isn't the required inverter so the piezo gets nothing!

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Guest Alun

Yes silly me, I needed an inverter not a follower, I knew this but for some reason I got the circuits mixed up!  ;D ;D ;D

You can use any op-amp but I recommended the CA130 because it boasts rail to rail swing and will give you the most volume, yes a LM741 will do but it won't be as loud. You could also use a hex invertor logic chip and paralell the inputs and outputs, you could also use a complementary pair of MOSFETs, or a bipolar transistors (with an inverter first) - they're many ways.

post-0-14279142169006_thumb.png

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Hey Alun,
Silly, silly you again and again!  :o 
Your 'fixed" opamp still won't work with its non-inverting input grounded. It needs to be at mid-supply.  ;D
With its gain of -1, your opamp would mirror the non-rail-to-rail output of the 555. It needs some gain to go full swing.  ;D
Nobody would notice the loss of about only 1dB anyway when using an opamp.  ;D
Where's your supply bypass cap? A 555 draws a supply current spike of up to 400mA when its heavy-duty totem-pole output switches, that would kill the battery's voltage for a moment without a cap holding the voltage up.  ;D

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Guest Alun

Oh of course, the one I posted before would be ok for a duel supply but not for single supply operation.

I never bother drawing bypass capacitors on the schematic, I just add them to the circuit when I build it. I put a 100nf on the supply of each chip or near any switching transistors, and a 10 to 100uf near the battery. I've added a 100nf to this circuit but you may need to use a bigger capacitor as well.

post-0-1427914216911_thumb.png

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LOL...  ;D

Oh I've been there a few times.... then again I'm still a newbie.... but even I know that once I've "Mastered" something I'll always find more to learn.

Thanks for going to the trouble Alun, I'll probably have time to breadboard this tonight. I'll post my results... well, I'll post whether it works or not... as for actual results... depends on my doggy. ;)

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Okay, I've built the circuit and it works well, I'll need to modify the trigger a bit, either a one-shot circuit or a long delay before resetting as the contacts may take a while to dry and stop conducting (if I'm not home).

Also, am I correct in thinking that the gain is set by the 10K resistor between the op-amp's output and the inverting input? Not that I'm likely to get much more out of it while running on a battery.

I did replace the 22K resistor in the R/C with a 100K pot... makes it alot easier to find the piezo's "sweet spot".

Thanks a ton Alun and everyone.

Do you guys think adding another 555 timer running astable would work alright if set with a cycle of something along the lines of: 5 sec. high, 10 min. low? I don't think it would work well, but if it's only gonna loose some precision I might be able to deal with it. If not, can anyone offer another suggestion?

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Hi CRE,
Changing the gain of the opamp won't make much difference because it already does exactly what the output of its driving 555 is doing, but is inverted. Maybe your piezo is drawing more current than the CA3130 can deliver. Measure its AC output voltage, it should be the same as the 555. Try a 741 opamp if it is too low.

I don't think a 555 will give a duty-cycle as extreme as the 120 to 1 that you were planning.

Since you are using a battery, I recommend using Cmos 555's for low power drain.  ;D

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Hey, wow, talk about a quick response...

As a matter of fact I am using a 741.... didn't have any other type of single op-amp on hand.

So as for volume, I'm either being limited by the piezo element or the single 9v supply... right? I mean, it's loud right now as long as the freq. is perfectly tuned, but I don't wan't loud..... I want downright terrifying!!!!!!  ;D

No, I'm not looking for ear damaging volumes either, but given that treble is directional I want to make sure my dogs hear it clear as day even though it's sitting on top of the refridgerator (of doom!). You know what I mean?

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Guest Alun

The output from the 741 op-amp will be about 4V less than the supply,  it would sound louder if the cmos op-amp was used because the output can swing from rail to rail.

A duty cycle of 50% is the best for this circuit and the circuit this is how the circuit is set up.

You might want to add another transistor on the input to make it more sensitive, but this circuit won't retrigger untill another pulse arrives. Try grounding the trigger and keeping it gounded untill the tone finishes, then connect it to posative and the circuit will reset.

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this circuit won't retrigger untill another pulse arrives. Try grounding the trigger and keeping it gounded untill the tone finishes, then connect it to posative and the circuit will reset.


Hmmm...... not sure what I've done wrong, but if I keep the trigger grounded the circuit doesn't stop until the trigger is pulled from ground.

I understand somewhat what you're saying about the op-amp, but as i said, right now 741's, 324's, 348's, and 1458's are all I have to work with.... the 741 being the only single.

I went ahead and tried 2 9v batteries in series and got buetter volume results.

I guess the thing which is on my priority list is the triggering. I need to find where I made the mistake that's keeping the trigger active beyond the specified time period.

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Guest Alun

You're lucky the poor 555 survived when it's only rated to 15V maximum supply voltage.

The triggering problem is probably due to you missing out the AC coupling capacitor or it's shorted or broken in some other way but 1nf capacitors rarely go wrong.

The trigger should look like this:

post-0-14279142171644_thumb.png

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Guest Alun

Just antother thought, it might be a good idea to add another pull up resistor on the input to ensure the AC coupleing capacitor discharges properly after trigering.

post-0-14279142171744_thumb.png

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Horay! Well, I swapped the ceramic cap I had in there (I wasn't positive of the value) and put in a 10nf Met. Poly. with the second pull up resistor and it works like a charm!

I understand the basics of most parts of this circuit, but the cap and pullups escape me... I kinda see some of the picture, but I'm not understanding the whole thing... care to break it down for this nooB?

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Guest Alun

The 555 on the left hand side is a mono-stable, that's triggered when pin 2 is grounded. Pin 2 only needs to be grounded for a short time for it to trigger a couple of hindered nanoseconds will do. If it's kept grounded for longer than the delay it will stay triggered until it's taken  positive again.

When the trigger is grounded pin 2 will be grounded too as the AC coupling capacitor is not charged, as it charges up through R2 and pin 2 becomes positive and will remain so until the AC coupling capacitor is discharged and it's grounded again. To discharge the AC coupling capacitor just disconnect the trigger from ground and it will discharge through R1 and R2.

R1 and R2 are just pull-up resistor their value isn't criticle, the 1nf capacitor is an AC coupling capacitor it's value can be between about 470pf and 100nf. 1nf was recommended on the data-sheet because the RC time constant is so short it won't affect the delay much, your 10nf will a bit more but it won't be noticeable for the delay in this circuit.

The problem you had was because the capacitor was far too big or short circuited, it may have been a 100uf tantelum bead, so it's time constant was very long or infinite if it was short circuited.

post-0-14279142171853_thumb.png

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Guest Alun

You might want to make the trigger more sensitive, you can do this by adding a transistor. It's positive trigger now, the 100K protects the transistor and the 100nf capaciror filters out any noise.

post-0-14279142172025_thumb.png

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Guest Alun

By the way ignore the circuit in post 18 I used the old op-amp circuit with the + terminal mistake! ;D

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Guest Alun

Yes I forgot it in post 18, you do need the potential divider I'd just modfied an old coppy of the circuit, instead of the lastest version - ;D sorry.

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