Piezoelectric crystals, such as quartz, make very accurate and stable electronic vibrations. Clocks, radios and computers depend on them for precise timing. You can make your own piezo crystal-based circuits. In this type of circuit, the crystal works in conjunction with other timing elements to produce a stable resonant state. The crystal keeps the oscillator's frequency stable. Crystals come in a variety of fixed frequencies, from 32,768 to billions of cycles per second.
- Skill level:
Things you need
- 32,768 Hz crystal
- CD4069 CMOS hex inverter integrated circuit
- Solderless breadboard
- 22M-ohm ¼-watt resistor
- 680K-ohm ¼-watt resistor
- 15-picofarad 50-volt capacitor
- 27-picofarad 50-volt capacitor
- 9-volt battery clip
- 9-volt battery
- 22-gauge single-strand wire
- Wire strippers
- Frequency counter
- BNC-to-alligator clips cable
Touch a cold water pipe or other grounded metal object to remove static electricity from your hands.
Insert the CD4069 integrated circuit into the breadboard. It will fit over the horizontal groove in the board.
Insert one lead of the 22M-ohm resistor so it connects to pin 1 of the integrated circuit. Connect the other lead to pin 2. Connect one lead of the 680K-ohm resistor so one lead connects to pin 2. Insert the other lead into a free column in the board. Connect one lead of the crystal so it shares this column. Place the other lead so it connects to the integrated circuit's pin 1.
Insert one lead of the 15-picofarad capacitor so it connects to pin 1. Place the other lead into a free breadboard column. Insert one lead of the 27-picofarad capacitor so it shares this column. Connect the other lead so it shares the column the crystal and 680K resistor occupy.
Insert the red wire of the 9-volt battery clip into pin 14. Connect the black wire to pin 7.
Cut a 2-inch wire and two 5-inch wires and strip ¼-inch of insulation from each end. Connect the column shared by the two capacitors to pin 7 with the short wire. Insert one end of a 5-inch wire so it connects to pin 2. Connect the other 5-inch wire to pin 7.
Turn the frequency counter on. Connect a 9-volt battery into the battery holder. Insert a BNC-to-alligator clips cable into the frequency counter's front-panel BNC connector.
Connect the alligator clips to the 5-inch wires. The frequency counter should display 32,768Hz exactly. The last digit may waver occasionally.
Tips and warnings
- The spacing between the two rows of pins on the integrated circuit match the horizontal groove in the breadboard. Place the IC so it straddles this groove.
- You can use capacitors rated for voltages higher than 50 volts.
- The CMOS 4069 integrated circuit can be damaged by the static electricity on your fingers, so discharge it by touching a large or grounded metal object before handling it.
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