I'm a beginner in electronics and I found two quartz crystal oscillators, each one has two pins. Their numbers are:
sjc4.000a
ee4.000
Is it possible to know the frequency by knowing the numbers? If not, how can I know the frequency?
How do I use them in a very simple circuit?
Quartz crystal is not the same thing as crystal oscillator.
Quartz crystal consists of real physical crystal that has precise dimensions. The higher the desired frequency, the smaller the crystal must be. So it is practical to make them only in certain range (common values are 4 MHz - 40 MHz, and then low-frequency 32 kHz for RTCs).
It works by piezoelectric principle. Applied voltage causes it to contract and vice versa. At certain frequency, it gets into mechanical resonance which is projected into electrical resonance.
Quartz crystal oscillator is circuit that contains a quartz crystal and produces periodic signal. It can be integrated or constructed from individual components. One example is single-inverter oscillator.
The part numbers you provided are almost certainly form an 4MHz crystal.
A quartz crystal oscillator is a complete unit that contains a crystal, a circuit to make it oscillate, and a driver that produces a clean digital square wave output. These will have at least 3 pins (power, ground, out), but usually have 4 for mechanical reasons. They typically come in a metal can, which shields the sensitive crystal oscillator from outside fields.
Since your devices only have 2 pins, they are bare crystals, or possibly ceramic resonators. There are various topologies for the circuit around a crystal to utilize the crystal's sharp frequency function to get accurate timing. A common one is just a inverting amplifier with the crystal in its feedback path. For that kind of circuit to be accurate, the crystal must be specified for parallel resonant application. This will be the case if it is specified for a particular load capacitance whether parallel resonant operation is explicitly stated or not. This is the type of crystal assumed by all PIC microcontrollers with a built-in crystal oscillator, for example.
There are also crystals specified for series resonant application, which require a different driving circuit. This type will not be specified to require a particular load capacitance.
Usually the crystal frequency is stamped on its metal case. If the whole thing looks more like a blob with two leads coming out, then it's probably a ceramic resonator. Those work electrically much like crystals, are less accurate, but cost less and are mechanically more robust.
The numbers you show don't make any sense in terms of frequency, so are probably part numbers. Knowing where these devices came from may help in deciphering the part numbers. Or, they might not be crystals or resonators at all. A picture would help a great deal.
