wanted: fm stereo receiver

By rik
2008-09-24 12:39

This is an electronics question that has little to do with robots. But this forum seems a good place to ask it anyway.

For an upcoming diy project, I am in need of some advice on integrated radio circuits. For my 93 yr old grandmother I hope to build a radio that can do this:

receive fm radio stations (over a central antenna system, i.e. cable)
in stereo
drive two 4-8 ohm speakers
remember up to 30 preset frequencies
micro controller tells radio which station or which frequency to tune
produce Sound That Does Not Suck (STDNS quality)
perhaps will be expanded with a CD player
looks beautiful and compact (this would be a non electronics issue, so forget it)

I intend to build the case and the controls myself. Leaving anything off that might confuse the user. Not that my gran hates technology or is getting too old to learn how to operate gadgets. But because modern stereo equipment does not respect her desire for KISS designs and interfaces.

So please help me if you can. Do you know a suitable radio IC to start out with? Do you have experiences with these ICs to share with me? Does it take a digital input for frequency choice?

What kind of amplifier am I looking for? Another neatly packaged IC would be my preference.

Thanks in advance, 8ik

By BaseOverApex @ Wed, 2008-09-24 18:56

KISS for Inventors

Simplest is also best for inventors. I suggest you get your hands on a car stereo and a wallwart to power it with. In my other life, I design and build free one-off devices to help disabled people. I've used car stereos in the past specifically for their KISS interface.

PS - I belive this reply to be the first post on the new server....

By hootyhoo @ Wed, 2008-09-24 19:20

What is this for? Are you

What is this for? Are you trying to create a tabletop stereo? Something integrated into a wheelchair?

Also, 30 preset stations? That's enough to program every single local radio station (depending on your area) that's what the tuner knob is for :)

By BaseOverApex @ Wed, 2008-09-24 19:38

Experience

My experience with this is that 6 presets on a car stereo is fine. Most people leave the tuner on the same channel all the time. Some have a daytime channel and a night-time favourite. Is granny an radio ham?

By rik @ Wed, 2008-09-24 21:02

30 presets - overkill?

Maybe 30 is too much of a good thing

I am comparing my design ideas with the "competition" of the existing set in Grandmother's living room. That one has (up to) 30 presets. I think I programmed no more than 20 and she only uses about, errr, six or so.

The car stereo has been on my mind as well. But I am also curious about programming a very basic interface myself. In a micrcontroller. I want some fun in this project for myself as well! And I read about one chip solutions, so I started to wonder if it could really be so easy. The datasheets so far are a bit intimidating...

If I were to present my gran with a radio that limits her to fewer stations she has got now, she would perhaps see that as a rip off. No radio ham. Just picky. Also, I want to program the presets for her. Not teach her how to do that and then use them. I want to literally (!) write the name of the station on each button/position/indentation whatever the physical interface. Never again would she have to wonder about which station she selected.

8ik

By BaseOverApex @ Wed, 2008-09-24 21:22

Random thoughts

Hide the unused buttons behind a facade is the easy answer.

You want a complicated solution for the sake of a complicated solution. I like that attitude. I can work with that.

So, I'm thinking firstly that a modern car stereo has an input for a remote control. You know the control on the stalk of the steering wheel? I works by applying a resistance across a pair of pins on the receiver. The buttons short (or open) resistors in the stalk such that a particular resistance corresponds to aparticular button being depressed.

A microcontroller connected by I2C to an electronic potentiometer could potentially be used to remote control the set.

Secondly, I'm thinking that a half decent radio has RDS, so teh display should always show the name of the selected station.

By rik @ Thu, 2008-09-25 10:09

RDS

Hmm, complex for complex' sake. Did I write that? I suppose I did. Sounds a lot like me anyway. Glad you agree though.

Yes RDS is included in a car stereo. No I would not like it in my design. One reason being: my gran complains about the readability of the display she has now. And I do not see a possible replacement that she could live with.

Another one: not all these stations provide a callname (that my gran would recognise). And then there is all that advertising on RDS. Is there a way to not display that?

By BaseOverApex @ Fri, 2008-09-26 17:35

On RDS

My only expeience of RDS is here inthe UK, where stations only put the station name. (So far as I can see.) I would doubt it can be switched off. The person who invents a way to switch off adverts will be a rich person, indeed! I hope they don't start putting scrolling messages on my display - I believe that would be a distraction and therefore a driving hazard.

By rik @ Fri, 2008-09-26 18:11

driving hazard

sure is! some stations give the locations of mobile speed traps through RDS -> double hazard!

By rik @ Thu, 2008-09-25 10:12

Remote control

Interesting to read about that. If I understand correctly, the RC unit has only a few (two?) wires running to the main unit. And the resistance measured by the unit codes for an input? Sounds a bit like an R2R ladder DAC-ADC arrangement?

By BaseOverApex @ Fri, 2008-09-26 17:43

S'pose

I'm no expert, but I would guess there's an R2R ladder, or at least a bunch of unique resistances in the remote.

By Chris the Carpenter @ Wed, 2008-09-24 22:16

I dunno about the reciever but...

Here is your amplifier circuit. http://www.instructables.com/id/Audio-Amplifier/

The LM386 is a great, simple amp. I have used it for this little guy and I also built a cute little USB-powered amp for my wife's Mac. Not only can you get it at Radio Shack for a couple bucks, but you only need a couple extra componants to make it go. --Simply a wonderful, cheapie amp.

By rik @ Thu, 2008-09-25 10:03

will check it out

Thanks, I will look into this amp!

By kahp-ho @ Thu, 2008-09-25 05:01

If you want something small,

If you want something small, I was just looking at this at Sparkfun.com. SPI or I2C interface. I don't have any experience with it and haven't even had time to read the data sheet yet. But since you asked...

Search there for FM Receiver Module, sku: WRL-08770.

Hope this helps.