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Forum Index : Microcontroller and PC projects : Alternate firmware for the silicon chip DAB+ radio project
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| skillet Newbie  Joined: 13/07/2020 Location: AustraliaPosts: 9 |
Second post for this morning from me. A mate and I have spent most of the covid time this year building and debugging the silicon chip dab+ radio project from back in early 2019. Along the journey of building the radio and getting it going, we each encountered more or less the same problems/bugs. Some of the issues were hardware design related, and the others were software related. One of the biggest disappointments with the original SC firmware was that although the hardware supported digital/optical toslink outputs, the original SC basic programme could only output digitally on AM and FM, but not DAB+. Another disappointment was that the sound of AM was very poor - the audio bandwidth was exceptionally restricted. By rewriting the basic programme, we resolved both these issues and others, and added a bunch of additional features to improve the radio. We figured we might as well share the new code... some of you might have built the radio yourselves and might enjoy the alternate programme, or even improve it further. I've added a lengthy comment at the beginning of the source code to explain how to use / configure it to your own preferences. It will also work more or less out of the box without changes, but I suspect you'll be curious and want to tinker. Merry Christmas! Alt_DAB_Radio_Firmware_v3.zip BTW: I encountered a bug with this forum server... you can upload zip files using the brave browser, but cannot upload zip files using safari. Edited 2020-12-30 08:23 by skillet |
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| morgs67 Regular Member  Joined: 10/07/2019 Location: AustraliaPosts: 78 |
Thank you both for sharing. I built this earlier this year and was disappointed with the SC design performance. The sensitivity was no where as good as a DAB/FM clock radio. I will now revisit it using your latest code and info. Thanks Tony |
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| skillet Newbie Joined: 13/07/2020 Location: AustraliaPosts: 9 |
Hi Tony, Interesting that you mention that sensitivity was an issue for you. I too had / have the same problem. Not sure if you've read the long comment in the source code I posted yet, but I describe some of the things I found and tried to work around in there. When I first completed the bog-standard SC design with their original SW, I found that I could not receive DAB stations at all at my home using the telescopic antenna. But I could occasionally receive a weak signal, but not enough for the radio to start to play the DAB stream reliably. When I visited my mate Ingo's home (guy who built one of these with me and worked on it together), he lives almost line of sight to the transmitter and the radio easily pulled in the signal and played perfectly. At my place, the radio was reporting around 40-45dBuV signal strength for the DAB stations it could receive (only registered one DAB frequency, not the two that are available in my area). At Ingo's it was reporting 50 and above using the telescopic antenna, and pulling in both DAB frequencies. Our experience is that unless the radio says its pulling in at least 50dBuV, its not going to work well with DAB. Ingo's an ex broadcast technician and has a bunch of test equipment I don't have. We played around with TV masthead amplifier to boost the signal - that worked great for me at my place getting an extra 15-20dBuV of receive signal strength. At ingo's place, the radio reported way less boost with the amp than at my place, but using his spectrum analyser, we could see that the real received signal strength was much higher than the DAB radio reported, and that as you wind up the received signal strength, the DAB radio tracks the extra signal power linearly to a point, but then according to the radio, beyond that point the increase in reported signal strength slows down, eventually stops increasing and then apparently goes backwards as signal continues to increase. So you can't really trust the radio's reported signal strength, or at least it helps to know the quirks. I believe the lack of sensitivity of the SC radio design (on FM, as well as DAB) is a combination of sloppy component choices in the VHF analogue front end part of the circuit, sloppy PCB layout (not controlled impedance traces / layout), and the SW using the VHF tuning parameters for the Silicon Labs (radio chip) reference design rather than recalculating the VHF tuning params for the SC VHF analogue front end and PCB. I managed to get approximately 3dBuV or maybe a little more by playing with the tuning params, (you'll see this referred to as ANTCAP settings in the basic programme and data sheets / application notes referenced in the basic programme), and it was really obvious after going through this exercise that much better improvement was possible if the PCB layout and component choice in the VHF front end was improved - but of course you need a new PCB design and different components for this. Not sure about you but it is totally beyond me to work with components so small and so densely packed on a surface mount project like this radio - its almost like you need a robot calliper to work on it! Anyway, if you connect the DAB radio up to your home's TV/FM antenna, I'm pretty sure it will work well for you as it does now for me. If you planned to use the telescopic antenna, then I suspect that the sensitivity is going to be the frustrating issue. If you can contrive to get a decent signal, the radio itself is actually truly hifi.... the performance of FM and especially DAB via an external DAC is truly excellent compared with the so-called hi-fi tuners I've had in the past. Even AM, although mono, sounds almost as good as FM when you've set your AM antenna up right. (The AM performance was another thing that the original SC software didn't do well with, defaulting to 3.5 kHz of bandwidth.... Try setting the AM bandwidth up to its max setting of 10 kHz in our software and you will see what I mean). Cheers Stefan |
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| morgs67 Regular Member Joined: 10/07/2019 Location: AustraliaPosts: 78 |
Hi Stefan, Thank you very much for the details of your investigation of the front end. Your antenna cap program is invaluable for checking any mods that I make. I intend to remove the very small inductors used for VHF and try some old fashioned larger coil(s). Also will investigate using a tap on the coil for the antenna connection. The CATV system where I live notches out the FM band and DAB is not that strong. Anyway, this will keep me busy for a while! Cheers Tony |
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| skillet Newbie Joined: 13/07/2020 Location: AustraliaPosts: 9 |
Thanks again Tony, I am really keen to hear how you go with the mods to the front end and am interested in repeating on my radio if you make headway. Not sure how you plan on implementing the modifications given the difficulty working on that part of the board, but I am also interested to hear your experience and understand your approach. If you make progress, I will surely try and follow. Good luck and I look forward to hearing how you go. Stefan |
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