I’m working on a personal project, and I could really use some help. I’m not an electrical engineer, so I apologize in advance if this is a basic question, but I’m a bit stuck.

I paid someone to design a personal alarm PCB board for me. It’s similar to those cheap $10 alarms you find on Amazon, but this one operates via a button instead of a pull pin. Everything seemed to be going well until I tried to order the PCB through PCBWay.

The issue I’m facing is that one of the items in the Bill of Materials (BOM) is missing a DigiKey Part Number, and PCBWay needs this to complete my order. The part that’s missing the Part Number is an inductor (L1), which is located close to the Piezo Buzzer on the board.

Unfortunately, the person I paid for the design has stopped responding, and I’m struggling to figure out what specific inductor I need. I’ve done my best to research and understand it on my own, but I’m feeling out of my depth here.

This project is important to me because I’m making this device for my grandma, and I want to get it right. I’ve attached images of the BOM, schematics, pick and place files, 3D render of the PCB board, and anything else that might be relevant. I also attached a zip file of the fabrication files (gerber/drill).

If anyone can help me identify the correct inductor or guide me on what to do next, I would greatly appreciate it!

Thank you so much in advance for your help!

 

Hi,
This is probably the answer you don't want.
Me, I would fit a buzzer that was loud enough. Forget the inductor.
You need a buzzer, not a piezo sounder.
I'm sure this will trigger someone with a better suggestion.
Good luck.........

 

You don't need the inductor.
In order to satisfy PCBWay's requirements, simply replace it with a 10nF capacitor or a 100kΩ resistor, or leave it out altogether. It would make no difference to the operation of the circuit.

 

Mr Chips, I do not agree. I think the inductor is there to to generate a high voltage spike when the mosfet stops conducting. this high voltage spike will increase the sound level from the piezo sounder. It is also possible that it's value is designed to resonate with the capacitance of the piezo sounder at the drive frequency.

Edit. I think a bigger problem will be that the files do not seem to contain the code to program the ATmega328P.

Les.

 

The device is labeled as "Buzzer". To me, that means it has its own internal oscillator.

 

"The device is labeled as "Buzzer". To me, that means it has its own internal oscillator. " ... but if you look at the digikey part number for the "BUZZER" you will see that it does NOT have it's own driver ... https://www.digikey.com/en/products/detail/pui-audio-inc/ab1290b-lw100-r/4147326

That said, a Piezo will act like a capacitor and need a path to discharge. Otherwise, once "charged", all you might here are very faint clicks. The addition of an inductor does indeed provide a discharge path, but additionally causes a voltage spike in the reverse polarity direction and because of this increases volume dramatically, but if you don't need the volume then a resistor would work just fine as a discharge path. Since the impedance of the "BUZZER" is 500 Ohms, then I would start with a 470 Ohm resistor. (470, simply because it is the closest common standard value) ... depends also on what voltage VBAT is ... as a general rule of thumb for every 5V factor 500 Ohms ... So 12V would be 1.2k ... 15V = 1.5k ... etc.


And then there is the code for the Micro. Does the OP have this code?

 

I did not look at the BOM.
The link provide is for "Buzzer Element", not "Buzzer".
This is a piezo-electric transducer. The DC resistance is infinite.
The impedance is listed as 500 Ohms. This is the reactance, not resistance.
The capacitance is 8 nF @ 1 kHz.
Hence, L1 and Bz1 have to resonate at the desired audio frequency.

It says that the resonant frequency is 9 kHz, which is beyond my audible range.