Build your own Audio-Guestbook for any occasion!

2025-08-14 | By Will Siffer

License: Attribution Non-commercial Audio Solder Teensy

Background

There are numerous trends in the wedding industry in 2025. From photo booths to audio guestbooks and from mirror signs to glowsticks, it feels like everyone has found a way to capitalize on my special day by offering simple electrical devices in a pretty box as a service. In this case, I am focusing on the trend of audio guestbooks. For the “low” price of $375, a company will ship you a retro-looking phone that records a message whenever someone picks up the phone. After the event, you ship the phone back, and they send you the contents of the storage drive.

I took one look at this and thought there must be a better way. Surely someone has figured out how to record audio through a phone, and I can make it myself, right?

Well, it turns out there were a couple of projects made, and I found one that used only 2 components: a Teensy 4.0 and a Teensy audio shield. Once I ordered the parts from DigiKey and found a phone from a local thrift store, I was ready to build!

The Process

It turns out that this is actually a pretty simple project once you have all of the materials. I was able to put it all together in an afternoon, so I would bet most people reading this could get it done in a weekend with minimal issues.

The first step is to find a phone that could be used for the project. Fortunately, you don’t have to be too picky here, other than with color and style, since most of the time, if the electronics don’t work, it is because of the internals, not from the actual speaker or microphone hardware.

The hardest part is identifying the wires in the phone for the speaker and the microphone. In the case of my phone, those wires were labeled, and I was able to identify them and cut them from the PCB for me to solder onto the Teensy 4.0 audio shield. The speaker isn’t polarity sensitive, so it is not as important which wire is grounded and which wire is attached to the mono output. The microphone, however, may be polarity sensitive depending on the hardware, so if you do not have a labeled board, you will want to make your best guess and be ready to swap them if things don’t work.

Circuit Labels

The last hardware piece was the switch to detect when the phone was lifted. I used a multimeter to determine which pins were used on the limit switch in the phone, and soldered wires to the Teensy 4.0. Those wires will act as the trigger for the beginning of the recording, ensuring that the recording only occurs when someone picks up the phone!

Once everything was put together, it was time to upload the software. I downloaded the software from GitHub (credit to https://github.com/playfultechnology/audio-guestbook), but I noticed that there were a couple of issues that needed to be addressed first to make the phone act the way I wanted.

First, once the phone was picked up, it only stopped recording when either the phone ran out of battery, the storage device was full, or the phone was put down. Since I did not want to risk the chance that someone would not return the phone back on the hook, I added a timeout feature to trigger the phone to go back to the “ready” state once 2 minutes had passed. I figured that there would be very few individuals ready to leave a message over 2 minutes long, and if so, they could always leave another message.

The other issues were minor but were caused by some formatting issues that had been okay in previous versions of the Teensy / Arduino IDE, but with updated libraries, the syntax had changed.

The one other change that needed to be made was the message that was played whenever the phone was picked up. For that, my Fiancée and I picked up the phone and left a message as any other guest would, but in this case, it was the welcome message. Once we were done, I renamed the file “greeting.wav” and now every time the phone is picked up, the greeting is played.

These minor fixes are one of the many reasons why I was happy to build this device myself. Building my own version of the audio-guestbook meant I could make the device work EXACTLY how I wanted it, and I didn’t have to compromise functionality just because that’s how the product was shipped.

Lever

Nerdy technical details

If you are still reading this, maybe you are thinking about making one of these yourself. I hope so, it was a fun project. You may be wondering, though, “gee Will, this is cool, but what if my storage card gets full? How much space do I need?” Or maybe you want to know how much power it draws at idle and while it is recording?

Well, fear not, I have done some tests, and I am ready to share those answers with you!

First, when it comes to storage, this is another benefit of the limited recording time; a 2-minute recording of constant talking only took a few kilobytes, so I estimated that just over 10,000 messages could be recorded easily at worst case on an 8GB card. This is a huge number, but I still might upgrade to a 16GB card just to be safe.

Finally, in terms of power consumption, it only draws about 115mA when actively recording and only about 100mA when idle. On a 10,000mAh battery that is over 80 continuous hours on idle or 61 hours recording. My wedding will only be about 12 hours long from the first guest arriving to the last of us leaving, so I anticipate that won’t be an issue.

Final thoughts

There are so many things that are totally worth buying instead of “DIY-ing” especially when it comes to your wedding day, but for me, it was a fun project, and it gave me and my future wife something to bond over to make our own. Plus, for less than $50, we own something that we can use again for another occasion! Maybe we will even let one of our friends use it at their wedding…

Until next time, I hope you learned something today and were inspired by my motivation to save money and learn something along the way. My name is Will, and I am delighted to have the chance to share my project with you.