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DIY Retro Audio Player

Portable MP3 Player for Music and Audiobooks

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Inspired by 1980s tape recorders, this audio player was designed with ease of use and accessibility in mind. Despite its nostalgic appearance, it packs modern hardware. Powered by the ESP32, it plays music and audiobooks from a micro SD card, either on its internal speaker or though a headphone jack. A 2.8“ IPS screen and mechanical buttons make up the simplistic user interface. The software is built around the ESP32-audioI2S library by GitHub user Schreibfaul1.

Some of the key features:
· 2.8“ 320x240px IPS display
· Fully 3D printed case
· Integrated mono speaker and 3.5mm audio jack
· Easy to use interface with mechanical keys
· 8 hours of playtime with 4x AA batteries (20h without backlight)
· Automatically save and restore positions in audiobooks

PCB layout, source code and STLs on Github: https://github.com/CoretechR/Retro-Audio

Recently I was looking for a simple way to play audiobooks for a family member who is not used to touchscreens. As it turns out there are not many available options that are simple enough to use. As I have never worked with audio players or speaker, this seemed like a useful and straight-forward project.

Making it easy to use does not mean that a device has to look ugly. I tried to build something that looks like a finished product with inspirations from 1980s electronics and Teenage Engineering.

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  • Software

    Max.K06/20/2022 at 19:24 0 comments

    Decoding mp3 files is not easy, but luckily it is a task that has been solved before. I found the library ESP32-audioI2S to be an ideal starting point for this project. It includes all the necessary functions to play audio files from an SD card, including ways to fast-forward and read id3 tags. The creator of the library, Schreibfaul1, even added support for very long audiobooks after I had trouble with those.

    While the audio library is feeding data to the amplifier, the user interface is displayed on the screen. This is done via a second library, TFT_eSPI. This makes it easy to draw the tape animation with decent efficiency. It might be even better to „pre-render“ the animation and just load individual frames from the flash memory, but I have not tried that yet.

    For audiobooks it is important to remember the position in a file. This means that the position has to be saves even when the power is switched off. There are multiple ways to solves this. Having a battery-backed SRAM is a good solution because unlike EEPROM or flash memory, RAM has unlimited write cycles. But eventually this extra battery is going to die and will need to be replaced. Instead of this I decided to use the available SD card and just limit the amount of wear. Saving the playback position only once per minute is enough for normal use. The data is written to a text file on the card, with every position being a new line in the file. Because all lines contain the same number of characters, restoring the position means simply jumping to the end of the file and reading the last line. This makes the code for saving and restoring short and simple while also saving the card from too many write cycles. The same method is used for saving the volume setting for the internal and external speaker. Now an audiobook can easily be stopped and resumed by simply turning off the device.

  • Hardware Design

    Max.K06/20/2022 at 19:14 0 comments

    From the beginning I knew that I wanted to go with a retro design. I had a few details in mind that I wanted to incorporate:

    The interface would be as simplistic as possible, with the classic buttons you can find on any cassette recorder. These recorders usually need big keys to actuate the tape mechanism. Regular mechanical keyboard keys are similar in size and travel, so these were ideal for the project.

    Cassette Recorders also have a nice way to show the tape reels rotating through a window. Instead of the physical tape, a screen would be used to show an animation of the spools. The sharp memory LCD would have been perfect for this, but without a protective cover, it would have been too fragile for a portable device like this. So I instead opted for a regular color LCD.

    Usually, rechargeable Lithium-Ion cells are the go-to option for something like this. But with the retro-tone of the project, regular AA cells seemed more fitting.

    With the buttons, screen and 4x AA batteries selected, the overall size of the device was set. I started to draw some concepts in Fusion360 that would allow me to arrange all the components while needing only a single custom PCB. These first designs looked really flat and boring.

    When I searched the web for some inspiration I came across the Philips 113, a portable record player from the 1970s. From this I took over the color theme and smooth shape.

    As most of my previous 3D-printed cases, this one is also made up of two half shells that are connected together by screws. I also included draft angles and a separation line to add to the molded part look. On the bottom a battery holder is secured in its slot, which has a 3D-printed cover that locks in place nicely.

    A custom PCB is necessary for the electronic components. Because of the raging component shortage the selection of processors was limited to pretty much only the ESP32. It has plenty of power to drive a display while decoding audio. The integrated WiFi means that features like internet radio can be added later through a software update. The ESP32 also has a I2S peripheral for an external audio amplifier. For this I selected the Maxim MAX98357A which is a common mono amplifier. Even though there’s only one internal speaker, I would have pick a stereo amp. But most of these devices are out of stock indefinitely. This means that a headphone that’s plugged into the 3.5mm jack also only plays mono audio. This is unfortunate but acceptable for an audiobook-centered device. Audio files are stored on a micro SD card, for which the PCB has a slot. The SPI display is connected through cables, which allows the top and bottom halves of the case to be separated later. To deal with the wide voltage range of AA batteries (1…1.5V), the 5V display gets its own boost converter. 

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Discussions

DamnFineCo wrote 4 days ago point

I love this design, would you be able to release the source files for the STL's? I'd like to adapt them for a 3.5" screen I have on hand.

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Max.K wrote 3 days ago point

Thanks, 3.5" might be a a bit much, depending on the PCB size. You have a PM.

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Ben wrote 6 days ago point

I love the aesthetics of this project. I'm curious what brand of filament you used for the top case.

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Max.K wrote 6 days ago point

Thanks, the filament is from "DasFilament": https://www.dasfilament.de/filament-spulen/petg-1-75-mm/176/petg-filament-1-75-mm-melonengelb

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Nazwa wrote 06/22/2022 at 21:55 point

1. please add usb host A for normal pendrive

2. second knob for adjust sound time , keyboard is not easy

3. is possible using different power? 18650 or(and) AA and meybe solar panel too?

4. in old good time i can give  my cassete to my friend. today, meybe put sound on 2d bar code or ... irda. yes this is still very good idea. irda not must working every time, only time to time

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powiadam.ci wrote 6 days ago point

yes adjust time in audio book or longest file is difficult with keys, i prefer knob

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Max.K wrote 6 days ago point

Thanks, those are a few good points if I every make a second version. Maybe I can even use the volume knob for scrubbing while holding down another key.

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Emmanuel wrote 06/22/2022 at 08:08 point

Fantastic idea and wondefull execution ! This gives me some ideas to replace the overkilled built I did for my son's speaker (RasPi + Bluetooth remote + USB)

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Max.K wrote 6 days ago point

Thank you! Yes, it might be a good shape for a DIY "Tonies" speaker as well. Maybe I should continue with this projects and add some more software features. A lot of the ESP32s functionality is unused right now. I'm thinking about a web radio, with the appropriate 80s style radio interface.

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zpekic wrote 06/21/2022 at 00:18 point

Super cool idea and great retro look too! Could it be slightly extended to be usable as cassette tape "mass storage" for home computers of the golden era? 

https://hackaday.io/project/175680-cassette-interface-for-fpgas

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