Accessible FM Radio Case Study - Part 1

[Part 2] [Code and Design Files]

In this series of blog posts, I am going to document my journey (which I am about to start) in designing a FM Radio receiver for which I have the very specific requirement of being usable by my brother, who suffered a stroke a few years ago. This has left him with cognitive impairment and use of just his left arm.

This blog will effectively form my notes, and follow my usual design process which is:

1. Investigate technologies
2. Create 'spike' examples to de-risk various aspects of the design
3. Breadboard or strip-board prototype
4. Testing
5. Prototype PCB creation
6. Enclosure and user testing

As I hope this will end up in a design that will help others, I am going to release all the CAD and firmware files under an open license. 

User interface

• Volume control - rotary, a pot, therefore with absolute positioning and no turning down to silent.
• On/Off switch - probably a stylish toggle switch, but low physical resistance and ok for one handed operation without having to hold the radio.
• Three preset buttons. Real switches with an indicator to see which is selected. Obvious icons (probably on paper) to select the channel. Talk (BBC Radio 4), Classical (BBC Radio 3), Pop (BBC Radio 2).
• A separate interface (behind a panel - or using a BLE phone app) to configure stations

Other requirements

• Large capacity LiPo battery power
• USB charge and pass through
• Decent power amplifier and speaker
• FM broadcast receiver (*)
• Bluetooth audio for wireless headphones
• No eye-pokey antenna
• Stable enclosure (one-hand friendly)

* Why FM rather than DAB or Internet Radio. Well DAB is power hungry and offers no real advantage (except perhaps future-proofing) over FM. 

As for internet radio? Well, this was my first thought as it solves the antenna problem. However, when I have looked at this before, it's quite difficult to get stable URIs for station streams, especially for BBC stations, which is likely all my brother will listen to.

Looking at what was commercially available, I found this: 

Which is actually pretty close to what I was planning. And if all else fails, I could easily see myself getting one for my brother. However, although you can't see it here, it has an eye-poker antenna and is powered by D-cells. Neither of which I am keen on.

Technologies

At the moment, my initial list of technologies to experiment with includes:

• A PCB antenna (as used in 'shark-fin' car antenna) -- this is the big risk, and subject of my next blog post.
• The  RDA5807M radio receiver IC (I might also try TEA5767 to see which is more sensitive)
• An ATTiny1614 microcontroller 
• A power amp probably D-class. Ideally 10W or more

I've ordered some RDA5807M modules from Aliexpress and started designing a PCB FM broadcast antenna using the research paper I found. I will need both the radio module and the PCB antenna for my first experiments.