WOGSD: Physically removing the buzzer from ACR122U

Winter of Getting Stuff Done is a seasonal theme I have set for Winter Season of 2020, based on CGP Grey's video. It's about getting stuff that I wanted to finish for some time done and not jumping onto new ideas all the time.

The issue at hand

ACS ACR122U is an inexpensive NFC reader/writer based on the NXP PN532 chip. It's what I do most of my NFC experimentation on.

Other than the limitations of it, I have one big issue with it: It has a loud, monotone buzzer.

Datasheet of ACR122U showing the buzzer, saying that it's monotone

You can disable it of course...

ACR122U API document showing APDU format to disable the buzzer

However it obviously does not persist between connections, and you cannot send APDUs to it unless there's a card on it. And it buzzes when it detects a card.

So, there's no easy way to prevent the buzzer from making a noise at least once using software alone, which I was reminded about again today by linuxgemini:

Linuxgemini's message pretty much summing up the section above

How I solved it

I already had my soldering iron and screwdrivers out from some stuff I was tinkering with this morning, and had my ACR122U out from last night. That made me wonder if there was an easy way to get rid of the buzzer.

I looked around on internet to see if anyone had done it before, but I couldn't find anything. Closest thing to an internal view I found was this, from this page on NFC Tools wiki.

So I took it apart (fwiw, the 4 screws are under the 4 rubber feet, I recommend putting a small screwdriver under the large sides of the feet to remove them with least pain and damage).

Inside of ACR122U

More inside of ACR122U, nothing too visible as a buzzer

I was a bit baffled as I couldn't see anything resembling a traditional buzzer, but I suspected that it was the big cube that had 1839+ written on it:

The suspected buzzer

But a quick search for 1839+ buzzer didn't give me much. However, I saw many similar ICs when I searched for SMD buzzer, which likely meant that I was on the right track:

Google image search for "SMD buzzer"

I searched around more, searching for '1839+" "SMD" buzzer, and found a page selling hard to find parts. One of them included CSS-J4B20-SMT by CUI Inc with date code 1839+:

Aforementioned entry of 1839+ with CSS-J4B20-SMT

I quickly pulled up the page for CSS-J4B20-SMT-TR, and indeed, it was a SMD buzzer. I searched more, and found the datasheet for CSS-J4B20-SMT too, and that was also a SMD buzzer. The one I saw on board didn't look that much like it, but I pulled out my multimeter and was able to verify that it did indeed have voltage flowing in this direction when it beeped.

So, I desoldered it. This is my first time actually desoldering an IC, so I'm happy that I managed to do so without damaging anything nearby (except a tiny bit of internal plastic, but it doesn't cause harm):

Inside of ACR122U with the buzzer removed

One concern we had with linuxgemini was that it may have been used as a resistor too, and I was worried that I might end up needing to solder a resistor in its place to make it work, but thankfully (as I am horrible with electrical engineering stuff) I didn't need to. I verified that it worked by reading the entirety of a card before closing it back up, and it succeeded.

So now I have an ACR122U that will never ever buzz again. Hurray. That's what I call a success. (And now I'm tempted to practice removing more ICs by borrowing linuxgemini's ACR122U and desoldering the buzzer on that too).