FM frequency read - motor control

Hello,
I am new to Arduino, I barely started looking into this. However, I have a project in mind which I think it can be done with Arduino.
I would like to build a Vintage FM radio but I think I will use a schematic without the big variable capacitor; this would not be a problem but I don't think I will find a capacitor in good shape + the whole mechanism for the scale. I am very interested in the looks and I would really like to have the frequency scale with the thin indicator on my radio.
What I had in mind was to read the radio frequency and "tell" a stepper motor to go to a specific position (via Arduino or an AVR). I think the mechanism would be way simpler and easier to control than the old capacitor + pulleys and strings. I think I would need a schematic and a code able to "probe" something in the radio schematic - read the frequency - move the stepper to a designated position on a defined scale (steps). Considering the FM band of 88-108 Mhz and the fact that the stations can have one decimal, this means I would need a 200 steps resolution for the motor (20Mhz bandwidth x 10 subdivisions/Mhz). Also, it would be nice for the stepper to know where it is because I will probably like to have both manual and automated tuning of the stations.
Does the above make sense? Is it doable and does anyone have an idea (probably even a schematic/code) for how to do it?

I appreciate all the help I can get. Thanks,
Mihai

Does the above make sense? Is it doable and does anyone have an idea (probably even a schematic/code) for how to do it?

What I had in mind was to read the radio frequency

How do you plan to do that ?

Is it doable ? I don't know . Can you do it ? You have to provide the schematic and decide where to probe.

If I had a schematic I probably would've asked different questions, don't you think?

This is an Arduino forum. What is the chance of getting a radio schematic on this forum do you think ? (50/50 ?)
When you have arduino hardware or software questions, this is the place to come. Are you there yet ?

I am not looking for a radio schematic. I am looking to translate frequency to a stepper motor using Arduino.

I am looking to translate frequency to a stepper motor using Arduino.

No that will not work.
An FM radio tuning is not a precise position. The exact position depends on a lot of things and they drift with time. So if you mechanically return to the same physical place it will not correspond to the exact tuning.

If you still want to go ahead and experiment then you need an end stop detector to get the absolute position of the motor, and then just step a fixed number to bring it "on tune"
Drive it like you would drive any other stepping motor, do not expect to find that someone has done the exact thing.

You need micostepping capable driver like the A4988 from Pololu.

You can certainly create an analog meter with an arduino and a stepper or servo. After all this is essentially the way speedometers work nowadays.

I'm not looking for absolute precision, if you remember the scale of the old radios they had that "thin" indicator across it. I'm just looking for something to move around with frequency to an approximate designated position.
For example, if I consider the 88-108Mhz band, given my initial example and considering d0 = 88Mhz then 98.1Mhz would be 101 steps from the origin. Now, if the needle/motor stops at +/- 2 steps then that would still be fine.

I would like to build a Vintage FM radio but I think I will use a schematic without the big variable capacitor;

Sounds more like an old AM radio.

I suggest to build the radio first, with a knob for manual tuning. When that is finished and working to your satisfaction, lots of people will be happy to help you with ideas for motorizing the knob and driving it to a given frequency.

Now, if the needle/motor stops at +/- 2 steps then that would still be fine.

You will get absoloute mechanical precision. But that will not always correspond to the same point in the radio spectrum. What you are doing is changing the frequency of an oscillator. You can measure this but not directly with an arduino. It is too high for accurate direct measurement so you will have to build some external circuitry to do this.

I don't think he is. The stepper is just an indicator, and not connected to a capacitor. He will determine the frequency some other way.

I found in an old AIWA FM tuner schematic that the frequency is actually taken from the FM oscillator. In this schematic, the frequency is probed to be shown on an LED display so I think my project could work the same way.

As jremington was saying, perhaps I should build the radio first and then motorize the knob and play around with displays and lights.

jremington:
I suggest to build the radio first, with a knob for manual tuning. When that is finished and working to your satisfaction, lots of people will be happy to help you with ideas for motorizing the knob and driving it to a given frequency.

Another idea which popped to my mind is to buy an FM tuner from the flea-market, something decent from the 80’s or 90’s and simply strip it and build around it.