Single Station Radio

[zach dunham]

Hello Adafruit Forum!

I'm trying to construct a single station radio using the si4735 chip with an atmega328 and an analog devices ssm2305 class d amp. The goal is to have a compact radio that can be tuned once in the coding and powers on to a specific FM station. Basically this project is coming from having used the si4735 shield that sparkfun was selling in this manner, but now trying to pair it down with fewer components. I am getting ready to prototype this and I was wondering if anyone had any creative insight, or at least could point out any glaring errors.

Thanks!

Radio
http://www.silabs.com/Support%20Documen ... 35-D60.pdf
Amp
http://www.analog.com/static/imported-f ... SM2305.pdf

[zener]

That's really cool. Of course the board layout will have a lot to do with the success of it. It can be quite important especially when working with RF. The only comment I can make at this point is about mono mode. I am not sure you can tie the L and R outputs together like that. Ideally the part has a mono mode but I didn't see any mention of that in the data sheet. Is there some other document with the command set?

[zach dunham]

Hey Zener -
Thanks for the post! Yea, I haven't begun laying it out yet, but I'm sure I'll have million questions once I do. I did see that you can force mono mode on the si4735 by setting the fm blend mono threshold level (pg 23 and 28 on the data sheet for the si4735), so I guess leaving the R output floating and connecting my coupling cap to the L out only would work then.
In the Sparkfun shield Vdd and Vio on the radio were connected to a digital pin (8) on the mcu via the hex converter (which I've omitted because I'm using a 3.3V atmega board); is there a problem trying the radio directly to power with the proper filtering caps like I have in the schematic?
Also, do you have any specific recommendations for layout, or the FM antenna section of the board?
Thanks!
Zach

[zener]

On page 41 of the datasheet are the 'Additional Reference Resources". You need to study those, especially: "AN383: Si47xx Antenna, Schematic, Layout, and Design Guidelines"

[adafruit_support_mike]

That is an awesome project. We expect updates.

One tip for making the transition from design to hardware: make the first version of the circuit "ugly":

http://wdv.com/Electronics/Fab/Manhatta ... niques.pdf
http://www.w4qr.org/files/home-brewing- ... -radio.pdf
http://cds.linear.com/docs/en/applicati ... an47fa.pdf

It's a common and highly respected construction technique, especially for radio gear. Working from a sheet of copper clad gives you a good ground plane, and you can actually build critical sections better in 3D than you can on a PCB.

[zach dunham]

Thanks for the links Mike!
I'll definitely post updates soon.
Cheers,
Zach

[zach dunham]

Hello!
We've made a bit of progress on this project and currently have our hardware and software files on github here -> https://github.com/The-Public-Radio for anyone who's interested. Occasional updates are also being made here -> http://yourpublicradio.tumblr.com/. We're still trying to improve our FM reception though and would appreciate any feedback anyone might have with regards to the board layout and antenna design.
Cheers!

[zach dunham]

Hey all,
I thought I'd share a link to the Public Radio updates page. We've made a bunch of iterations since the last post, including using a mechanically tuned, digitial IC.
Holler at us, share your thoughts. It's all on Github, here
Thanks,
Zach

pcba-1.jpg (502.47 KiB) Viewed 1061 times

[adafruit_support_mike]

That's a nice looking little device! You've obviously put a lot of time and effort into the design.

[zach dunham]

Hi all,

I thought I'd post another update and say that this project is finally live on Kickstarter! We'd love it if you checked it out.
http://kck.st/1qloI7f