I'm trying to find out what the device is called that is found on a car radio. The dial that you turn to change stations. I want to track one down to see how it works, but I have no idea what it's called.
Does anyone know?
I'm trying to find out what the device is called that is found on a car radio. The dial that you turn to change stations. I want to track one down to see how it works, but I have no idea what it's called.
Does anyone know?
In older radio's this was the variable capacitor that (in the common super type radio's) determined the frequency of the first stage and the oscillator, effectively selecting the single radio station you wanted to hear by analog means.
In modern radio's I guess it is a rotary encoder. You can tell by the subtle clicks you feel when you turn the dial. This rotary encoder is in effect two switches, that inform a microcontroller how the dial is turned. (This answer illustrates how a rotary encoder works.)
The last dial-type auto radio I saw used a variable inductor, basically a slug that was pulled along the axis of a hollow form with a coil wound on the outside. It'd be hard to find one of those for sale today (it isn't a kind of tuner that can easily be mated to digital controls and readouts). The vibration in an automobile was not conducive to the use of air-variable capacitors (another tuning knob component of yesteryear). There were variants of the tuning capacitor with plastic-sheet insulation that were possibly used, the floppy plates wouldn't matter if the plastic maintained a constant thickness. Variable capacitors are expensive, but probably can be found.
Nowadays, it's likely your radio uses a no-moving-parts tuner based on the capacitance variation of a "varicap" diode with voltage. The knob would be a position encoder, reporting clockwise or CCW rotation to the control computer.
To tune a radio it is usual to vary the capacitance in one or more "tuned circuits"*. Occasionally inductance is altered but this is less common.
In radios that are fully electronic the control dial or buttons interface with a microcontroller (small computer) that alters the capacitance of an electrically variable capacitor. An electrically variable capacitor is known as a varicap (not surprisingly) or a varactor or a varactor diode.
In older radios the capacitance was varied using a device called a "variable capacitor" (again no surprise :-) ). This is what you are most liable to find useful for initial investigations.
Added: In some cases when systems are tuned by varying inductance a brass slug is inserted into the coil to progressively REDUCE the inductance. This is not usual and the effect is usually proportionally much lower than increasing inductance by inserting a "ferromagnetic" core such as ferrite or powdered iron.
Images here http://bit.ly/VariableCapacitors
Explanation here http://en.wikipedia.org/wiki/Variable_capacitor
Varicap here (brief) http://en.wikipedia.org/wiki/Varicap
Build your own !!! :-) http://www.crystalradio.net/beginners3/cap.shtml
Tuned circuits