Home >> Hobbies >> Other Hobbies

How to Create an Analog Waveform Circuit

In electronics, an analog waveform circuit generates a steady frequency by amplification or by charging and discharging a capacitor. These circuits are generally called oscillators or function generators, and hundreds of different designs exist. A simple circuit called a relaxation oscillator uses a single unijunction transistor, or UJT, and a few resistors to cycle a capacitor on and off. The voltage across the capacitor has a sawtooth pattern, rising gradually to a certain point, then dropping quickly to zero before starting a new cycle.

Things You'll Need

2N2646 n-type unijunction transistor
Solderless breadboard
10-nanofarad, 50-volt capacitor
47-ohm, 1/4-watt resistor
9-volt battery clip
100K-ohm, 1/4-watt resistor
470-ohm, 1/4-watt resistor
2 10-inch 22-gauge wires
9-volt battery
Oscilloscope

Instructions

- 1
  Set the leads of the unijunction transistor into the breadboard. Note that the holes in a particular column are all connected together, and adjacent columns are isolated. You create connections by placing wires into the appropriate columns. Place each lead of the UJT in an adjacent column of the board.
- 2
  Insert one lead of the capacitor so it connects to the transistor's emitter lead. Put the capacitor's other lead into a free column. Insert one lead of the 47-ohm resistor so it connects to this column. Insert the black, or negative, wire of the battery clip into the column also. Set the resistor's other lead so it connects to the transistor's base 1 lead.
- 3
  Insert one lead of the 100K-ohm resistor so it connects to the transistor's emitter lead. Set the resistor's other lead into a free column. Insert the red, or positive, battery clip wire so it connects to this column. Connect the 470-ohm resistor between this column and the transistor's base 2 lead.
- 4
  Insert one end of a 10-inch wire so it connects to the column holding the black battery wire. Insert one end of a second 10-inch wire so it connects to the transistor's emitter lead.
- 5
  Connect the oscilloscope's probe tip to the second wire. Connect the probe's ground clip to the first wire. Attach the probe's BNC connector to the oscilloscope's channel 1 BNC input.
- 6
  Turn the oscilloscope on and set its horizontal sweep rate to 1 millisecond per division. Adjust the oscilloscope's channel 1 input to 2 volts per division. Snap a fresh 9-volt battery into the clip. Observe the analog sawtooth waveform on the oscilloscope screen.

Other Hobbies