Some of the devices under consideration.
We are looking for devices which could be easily modified into our prototype soundbox at the moment.
The device has to be capable of both recording and playing back a small selection of sounds. It has to be portable, and operate with as few controls as possible.
Previous work in this area used dictaphones, which are quite expensive, but provide very good sound quality. They don’t generally have a playback function, as they are intended to be connected to a computer for download and editing. This is a step which we would like to avoid with our device.
There are a multitude of cheap MP3 players on the market at the moment which are able to record and play back in a few formats, such as .WAV or .MP3. One of these has been disassembled for study:
It runs (or ran, rather- the battery leads snapped off during testing) on a small lithium-polymer battery, and is controlled through a small LCD screen by five pushbuttons on the front. It has a 3.5mm jack for headphones, and a mini-USB socket which can be connected to a computer to modify the contents of its memory, and to recharge the battery.
It is small enough to be easily inserted into a handheld case, and is definitely capable of recording multiple short audio clips onto its 4GB of flash memory.
However, the user interface needs a fair bit of navigating and some unintuitive button presses. There’s also a long delay when switching from playback or record to the main menu. Even if we were to replace the buttons with control by an Arduino, the delay would probably cause issues during use.
The MP3 player, despite having a ‘record’ function, did not actually have a microphone. Soldering one onto the PCB solved this.
Sound quality is fairly poor, with a lot of noise and a continual beeping.
We have also considered making a video capture device, and have done some similar tests on this “Trevi VideoMemo Recorder”. It is very simple to operate, and can record up to three different videos. It can be switched from recording to playback quite quickly, and does not have a complex GUI.
There’s no way of extracting the data from its memory, as the device does not have a USB or other data socket. It also runs on AA batteries, or any other source of 3V DC. It’s also considerably larger than the MP3 player.
During testing, it was found that the VideoMemo has what looks like a slot for a mini-SD card silkscreened onto its PCB (circled in the image to the right), but there’s no socket attached by default- this could provide extra storage space or a way of extracting recorded sound and videos if one was attached.
Some other possible devices to be looked at include the circuits used in greeting cards, MP3 shields for Arduino microcontrollers, and stand-alone barebones MP3 player circuits.