DAB Digital Radio LM3886 Amplifier - Summary
1 - Intro, 2 - Investigation, 3 - Design, 4 - PSU and Amp, 5 - Control Board, 6 - Software, 7 - Summary
Conclusion
At the time of writing, the radio has been running for 7 months and I've not had any problems. I did invest in a DAB aerial for better reception on thick cloud / rainy days as the signal strength can sometimes struggle, but a better aerial solved that.
Sound quality is great. Certainly the best DAB receiver I've owned or built, and even constrained at +/-25V still allows the amplifier to give some real decent volume levels when called upon.
I'm also pleased with the look of the unit, but it's mainly a pleasure to turn on that rotary power switch and let it tune to my favourite radio station and get me through a day of working or relaxing at home.
The build was also enjoyable, even though getting the I²C handling to work on the PIC began to get a bit frustrating, I learnt a lot about it and broadened my knowledge of embedded computing.
It's many times better than the Bush radio the components were salvaged from - which looks like something you'd find in a landfill, because with it's original amp, speaker and aesthetics, the quality was so bad. I certainly picked it up really cheap because it was unwanted, and I'm pleased with the improvements I've given it, and used some other spare electronic components taking up space in storage too.
Because of this, excluding speakers and aerial, I think I spent less than £60, most of that being on the case. If you were to buy the amp, transformers, PSU etc though you'd be looking at £150 or higher I suspect. Easily worth that cost in my view though :-)
Radio in position and operating with cover off
Top view with cover off
View of control board and DAB module, input rotary switch on the left, speaker terminals on the right
View of transformers, mains connections, fuse holder and input socket
View of amp PSU capacitors, with LM3886 amp on the left, preamplifier on the right
View with top cover off
View with top cover off taken from the back
View of the back heatsink, speaker connectors and phono sockets
Operating position, before I added labels
Operating, with labels
Error displaying some characters
During listening, I did notice some weird characters appear on the display on rare occasions.
It's supposed to read Amy Lamé
I expected them to be unicode character codes and that my display was not configured to map the codes correctly (i.e. wrong character set), or that C0 character that was separating out each character was changing to something else for these characters and the remainder was output wrongly.
Analysing the HD44780 datasheets gave no clues. The characters that I caught displaying did not match up (pixel by pixel) to any character set.
I then hooked up the logic analyser again, and found that the special characters were actually created by the DAB module I²C commands as custom characters.
Here's the decoded data foy your information:
| Sequence | Address | Data |
| 1 | 3E | 00,38,48 |
| 2 | 3E | 40,05,0A,0E,11,1F,11,11,00 |
| 3 | 3E | 00,38,50 |
| 4 | 3E | 40,0E,11,17,15,17,11,0E,00 |
This is two examples again, which translates as below:
Char 01 or 0x48
| 05 | |||||
| 0A | |||||
| 0E | |||||
| 11 | |||||
| 1F | |||||
| 11 | |||||
| 11 | |||||
| 00 |
Char 02 or 0x50
| 1F | |||||
| 11 | |||||
| 11 | |||||
| 11 | |||||
| 11 | |||||
| 11 | |||||
| 1F | |||||
| 00 |
And the text line, using characters 01 and 02:
| Sequence | Address | Data |
| 1 | 3E | 00,C0 |
| 2 | 3E | C0,20,C0,20,C0,20,C0,41,C0,6D,C0,79,C0,20,C0,4C,C0,61,C0,6D,C0,01,C0,02,C0,20,C0,20,C0,20,C0,20 |
Without C0 character: 20,20,20,41,6D,79,20,4C,61,6D,01,02,20,20,20,20
Amy Lam??
What I should have done instead was look at my other DAB radios at the same time, which give the same weird characters:
My Blighty portable DAB
My Sonichi S100 In-Car DAB
This means the fault is actually with the module, and it's a common fault, and correcting it would be very hard as it would need decoding of custom characters for every character that could be sent incorrectly.
On further searches, I came across this link https://worlddabeureka.org/2015/08/03/issue-26-new-latin-based-character-set-for-dab/
It indicates that in 2015 a character set change was to be made and that existing equipment would need updating. This looks a plausible reason.
Very few DAB radios have firmware updates. Certainly not this Bush one my module came from, and nor my car or portable radio.
I guess I'm stuck with this one, but it is only a minor problem - 99% of the time the text is fine.
Update: Problem seems to have gone away sometime in 2021 I think. Maybe the BBC changed something.