Weird Science

Ring Oscillator

Polish ver­sion is here

A Bit of The­ory

A mul­ti­vi­bra­tor is an elec­tro­nic cir­cuit con­struc­ted using elec­tro­me­cha­ni­cal relays, vacuum tubes or gas-fil­led tubes (inc­lu­ding neon lamps), tran­s­i­stors, tun­nel dio­des, or other swit­ching com­po­nents. It has two or more sta­ble or quasi-sta­ble equ­i­li­brium sta­tes. There are various types of mul­ti­vi­bra­tor­s—the most com­monly used type is the bipo­lar asta­ble mul­ti­vi­bra­tor. Besi­des their nume­rous prac­ti­cal appli­ca­tions, mul­ti­vi­bra­tors can also func­tion as LED fla­shers and visual effects devi­ces.

This pro­ject intro­du­ces a sli­gh­tly unu­sual and less-known type of mul­ti­vi­bra­tor: the ring oscil­la­tor, named for its cir­cu­lar con­fi­gu­ra­tion.

Con­struc­tion

To build the ring oscil­la­tor, you will need the fol­lo­wing com­po­nents:

Assem­ble the com­po­nents accor­ding to the sche­ma­tic dia­gram below:

Ilustracja

The cir­cuit con­si­sts of three sta­ges, each con­ta­i­ning one tran­s­i­stor. Each stage is con­nec­ted to the next, with the third stage fee­ding back into the first. This con­fi­gu­ra­tion cau­ses the signal (indi­ca­ting whe­ther a tran­s­i­stor is con­duc­ting or cut off) to cycle thro­ugh the sta­ges in sequ­ence. As the signal from the last stage is rein­tro­du­ced into the first, the tran­s­i­stors switch on and off cyc­li­cally. By con­nec­ting LEDs to indi­cate the state of each tran­s­i­stor, this cre­a­tes a visual effect where the LEDs sequ­en­tially light up and turn off. The fla­shing speed can be adju­sted over a wide range by chan­ging the capa­ci­tance of the elec­tro­ly­tic capa­ci­tors and the resi­stance of the base resi­stors.

Here is the cir­cuit assem­bled on a uni­ver­sal PCB:

Ilustracja:

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Only one capa­ci­tor is visi­ble because the others are moun­ted on the under­side of the PCB. The cir­cuit in action can be seen in the video below:

Instead of three sepa­rate LEDs, you can use a sin­gle RGB LED with a com­mon anode. An RGB LED inte­gra­tes three indi­vi­dual LED ele­ments within a sin­gle pac­kage:

Ilustracja

Source: http://www.lights-expert.com/b2b/pics/5mm_RGB_LED.jpg, acces­sed: 01/23/2015

Since two of the inter­nal LED ele­ments are always lit, their colors will blend, pro­du­cing inte­re­sting visual effects.

In the demon­stra­tion, the LED light is pro­jec­ted onto a white paper screen. Since the light from each color ele­ment doesn’t fully over­lap, the colors don’t mix per­fec­tly. This issue can be miti­ga­ted by pla­cing the LED inside a fro­sted dif­fu­ser. I used a fro­sted pla­stic film cani­ster, which pro­du­ced the fol­lo­wing effect:

This sim­ple cir­cuit is easy to build, making it an excel­lent pro­ject for begin­ners who enjoy visual elec­tro­nics pro­jects. Howe­ver, the ring oscil­la­tor is also sui­ta­ble for more advan­ced appli­ca­tions.

Enjoy expe­ri­men­ting with this edu­ca­tio­nal pro­ject! :)

Fur­ther rea­dings:

Marek Ples

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