Ive seen around this kind of shcematic. I dont have more details about the speaker, buzzer, piezo o whatever it is. Why is this schematic?
- Is the resistor just to limit the current? But if the buzzer doesnt sink more than 80mA it wouldnt be neccesary?
- But what is the use of the series capacitor? To block AC-DC current? To amplify?View attachment 217523

The resisttor is definitely to limit current and the diode is to suppress the imaginary inductive voltages from the electromagnetic speaker coil. The capacitor is there to block DC if the output device stays switched on for an excessive time. None of those components are required with a regular piezo sounder, since it is a lossy capacitor that dissipates power as sound.

 

The resisttor is definitely to limit current and the diode is to suppress the imaginary inductive voltages from the electromagnetic speaker coil. The capacitor is there to block DC if the output device stays switched on for an excessive time. None of those components are required with a regular piezo sounder, since it is a lossy capacitor that dissipates power as sound.

I understand. So that is like for a magnetic buzzer? Do you mean that piezo buzzers would need those components? So I guess piezo buzzers only have benefits hahahaha

 

hi G,
That symbol is for a loud speaker, not a buzzer or piezo.
E

 

hi G,
That symbol is for a loud speaker, not a buzzer or piezo.
E

Exactly. That is the symbol for an electromagnetic speaker. A piezo device is totally different and it generally has no DC continuity and so it does not need any of those components. In addition, it is a high impedance device whie speakers are mostly low impedance devices.

 

Im sorry about the symbol. It is the only suggested by the schematic program

I’m just learning the differences. Thanks so I won’t use them in my project, just the piezo connected to the 555

 

Since there is no latching function or toggling function in either concept there is no reason at all to debounce the switch contacts closing. In addition, the circuit was supposed to start making sound when the switch OPENED, which is not an action that produces contact bounce.
And the CMOS devices mentioned thus far will work very well up to at least 15 volts supply, and so there may not be any need for a regulator.

 

https://www.edn.com/increase-piezoelectric-transducer-acoustic-output-with-a-simple-circuit/

This a link where they show a resistor used to discharge the capacitance of the piezo. What do you think?

 

https://www.edn.com/increase-piezoelectric-transducer-acoustic-output-with-a-simple-circuit/

This a link where they show a resistor used to discharge the capacitance of the piezo. What do you think?

Clearly he link shows an exhaustive analysis far beyond my evaluation. It all makes sense as well. The one question is if there is a need for that great a sound level increase, and the resources required to make the analysis. That scheme will work with either the 555 concept circuits or the single-ended CMOS versions, but it is not applicable to the double ended CMOS version that I originally proposed, both because of the duty cycle part and the bipolar drive part.
So the question is how loud does it need to be for this application?

 

Clearly he link shows an exhaustive analysis far beyond my evaluation. It all makes sense as well. The one question is if there is a need for that great a sound level increase, and the resources required to make the analysis. That scheme will work with either the 555 concept circuits or the single-ended CMOS versions, but it is not applicable to the double ended CMOS version that I originally proposed, both because of the duty cycle part and the bipolar drive part.
So the question is how loud does it need to be for this application?

Loud its a relative term. Depends on each persona and the enviroment. I will place the keyholder (where the buzzer will be installed) close to the street so I just want it to be as loud as possible. Small and thin piezo I saw on the market supple 70-90dB depending on the supplied 1/2 square wave, resonant frequency and voltage. With that I would like to optimize as much as possible the sound to make it as loud as it could be

 

OK, so now there is a subjective design target: With that I would like to optimize as much as possible the sound to make it as loud as it could be. With a suitable amplifier and speaker it could be 95 Decibles at 10 feet, as loud as the siren on a passing fire truck. That is probably far more than the design target. And still the ultimate purpose is unclear. Making a noise when the key is removed seems to be the target, but why?

 

OK, so now there is a subjective design target: With that I would like to optimize as much as possible the sound to make it as loud as it could be. With a suitable amplifier and speaker it could be 95 Decibles at 10 feet, as loud as the siren on a passing fire truck. That is probably far more than the design target. And still the ultimate purpose is unclear. Making a noise when the key is removed seems to be the target, but why?

Why making a noise when the key is removed? Easy, not to forget the key inside as the door locks after is closed because it doesnt have a door handle to open it from the outside

 

Could you help me with the calculation of the power dissipation of the base resistor and transistor for amplification of the piezo transducer? This is to pick the right transistor and base transistor

I will be using:
- NPN transistor 2N2222A
- Base resistor, first I will use a low value like 270ohm
- Resistor between terminals of the piezo 1K as it is simplier than using diode+inductor; as the inductor values needed are something like 2-3mH and they area already big.
- Piezo https://www.cuidevices.com/product/resource/cpt-1203-78-smt-tr.pdf of rated 5mA

The article I am using to base my amplification is https://www.edn.com/increase-piezoelectric-transducer-acoustic-output-with-a-simple-circuit/

 

To determine component values for an amplifier you need to know how much gain you want and how much output voltage and current you need.

 

Well. How should I do that having the information I have related to the components?

 

hi,
If you examine the 555 output pin it is push/pull ie: active pull up to Vdd and active pull down to 0v, so why would you want to add a transistor driver thats only a pull down.?

Connect the piezo between pin 3 and 0V, and try check the sound level.

E

 

So now I am going to make a radical suggestion of a mechanical spring system to eject the key from the lock ater the door is unlocked to exit. If designed correctly the key would be pressed into the persons hand after unlocking the door to exit.Very reliable indeed.

 

hi,
If you examine the 555 output pin it is push/pull ie: active pull up to Vdd and active pull down to 0v, so why would you want to add a transistor driver thats only a pull down.?

Connect the piezo between pin 3 and 0V, and try check the sound level.

E

Yes I will try for sure before. But I want to understand why would people consider it, even I think that I saw the circuit in a CUI piezo datasheet. If the Piezo sources just 5mA why would people use the transistor if any MCU can sink normally 25mA. I understand why using a transistor to drive any device with a MCU is more reliable but why using it as the article proposed? I’m trying to understand and learn

So now I am going to make a radical suggestion of a mechanical spring system to eject the key from the lock ater the door is unlocked to exit. If designed correctly the key would be pressed into the persons hand after unlocking the door to exit.Very reliable indeed.

You still didn’t understand me. Think of a storage where the key is outside, the door doesn’t have a handler outside so your only way in is the key. You open the door with the key, you go in with the key and then you place wherever in the storage while doing other things. You go out of the room and the door closes but you just left the key inside

 

Yes I will try for sure before. But I want to understand why would people consider it, even I think that I saw the circuit in a CUI piezo datasheet. If the Piezo sources just 5mA why would people use the transistor if any MCU can sink normally 25mA. I understand why using a transistor to drive any device with a MCU is more reliable but why using it as the article proposed? I’m trying to understand and learn




You still didn’t understand me. Think of a storage where the key is outside, the door doesn’t have a handler outside so your only way in is the key. You open the door with the key, you go in with the key and then you place wherever in the storage while doing other things. You go out of the room and the door closes but you just left the key inside

I never set a key down! It is either in my pocket, in my hand, or in the lock. T learned that lesson 50 years ago and it still works well. It is a bit of work to develop that habit but it prevents a whole lot of problems. The most important thing is always put the key in the pocket. Then when it is forgotten it can be found quickly.
Of course it is very important to not have a hole in the pocket.

 

I received the parts and did my tests. The piezo works well, much better when used with a transistor and with a resistor across its terminals

I have an issue. The N MOSFET doesnt work as expected, my idea was for it work when the switch was open but it works all the way around. I think that the suited part would be a P MOSFET