On Friday, 31 January 2020 10:39:15 UTC, T i m wrote:
On Fri, 31 Jan 2020 00:21:10 -0800 (PST), wrote:

On Friday, 31 January 2020 00:41:11 UTC, T i m wrote:
Test for you then ... I'd like to build a simple FM broadcast receiver
that I can tune (and lock) to R4 for our daughter to listen to when
she's out walking the dog.
A kit would be nice but I don't want anything that scans, unless it
can be locked on a single freq (93.2 MHz?) at startup?
I think it would only need to drive a small speaker or single
headphone.
SiLabs make some very nice single-chip FM radio receivers.
Would that be this sort of thing John?
https://www.silabs.com/audio-and-rad...adio-receivers

Yes. Those ones allow you to use the headphone leads as an antenna.
There are some others that support a small loop antenna. Such loops are
narrowband, so the radio can autotune the loop for the frequency
currently being used. This gives much better performance than a fixed
tuned loop and compensates for varying proximity to other objects
such as the person wearing it when dog walking.

You can
control the tuning over i2c.

Ok.

Some versions have support for actively
tuning a loop antenna.

I'm not sure what that means and how it would apply it's use when
dog-walking. ;-)

See above

All you need is one of those and a small
microcontroller to preset the tuning.

So would require something like an Arduino Nano / ESP32 along with the
radio module *just* to do that (lock it to R4)? No way of mapping it
using jumpers etc?

These ones do need a microcontroller, but an ATtiny or similar minimal
processor should be enough.
You would need good soldering skills to use one of the SiLabs devices.
I have hand-wired prototypes with them in dead-bug mode but good magnification
and a steady hand are essential. I probably have a few lying around if you
want one or two to play with. I would need to check exactly which versions
I have.

I think I was thinking of something much simpler, possibly with just a
preset tuning cap, rather than anything digital that's probably going
to consume more power for no real advantage in this role?

The supply current is about 15mA at 2.7 to 5.5V. A small microcontroller
might add a few more mA.

I'm not ruling out the idea of a digitally controlled FM module,
especially if it might out-perform a more basic solution (stability
AFC/ AGC etc).

Part of the point was for me to give her something simple that just
did R4 with a volume control, and ideally at a budget price. I fear
once we start down the road of something 'nice', all be it locked onto
93.2 MHz, I might as well by a manually tuned small commercial
'transistor radio' and glue the tuning knob on R4. ;-)

Cheers, T i m

p.s. I have previously been given (as a promo) micro radios with no
display and a simple search button and volume control but they didn't
typically retain the last used frequency and would also 'search' on
their own if the signal dropped out for a second. ;-(