Home >> Science & Nature >> Science

How to Make Crystal Oscillators

An oscillator is an electronic circuit that produces a steady, output frequency. The difficult part of the circuit is keeping the frequency stabilized. Changes in temperature or load requirements can destabilize the oscillator and cause the frequency of the output to vary. One way to stabilize an oscillator is to put a crystal in the circuit. Each crystal has its own "resonate frequency" determined by the thickness and shape of the crystal. As long as the frequency in the circuit is close to the resonate frequency of the crystal, it will be stabilized.

Things You'll Need

Crystal
Transistor
Resistors
Capacitors
Wire
Soldering equipment

Instructions

- 1
  Choose a JFET transistor that matches the power requirements of your circuit. All JFET transistors are generally the same except for the power requirements. Locate the three labeled wires on your JFET. The wires are marked "S" for source, "D" for drain and "G" for gate.
- 2
  Develop the output of the oscillator across the "S" and "D" leads of the JFET by connecting the "S" and "D" wires from the JFET socket to the output terminals of your oscillator. Put a 20-microfarad capacitor between the D-pin of the JFET and the output terminal to electrically isolate the oscillator from the output.
- 3
  Connect the power supply to the oscillator through a radio frequency coil to keep the oscillator frequency isolated from the power supply. Any radio frequency coil with an iron core that is rated more than 100 millihenrys will suffice. Connect the other end of the coil to a post that will have three other wires connected to it.
- 4
  Run one wire from the post on the non-power side of the coil to the 20-microfarad capacitor that goes to the output. Run another wire from the post to the D-pin of the JFET. Connect the third wire through the crystal and a 30-picofarad capacitor to the G-pin of the JFET. This last connection is the feedback circuit that determines the frequency of the oscillator.
- 5
  Place a 470-kilo ohm resistor between the G-pin and the S-pin of the JFET to provide the correct biasing to make the transistor work properly.

Science