Talk:Relaxation oscillator

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Generic relaxation oscillators too[edit]

I think this page is too specific. There are other types of relaxation oscillators---your heart and circadian rythm, for example. I think this page should be changed to focus on the concept of how an accumulating signal and thershold for release can be used to construct a relaxation oscillator. neffk (talk) 20:14, 4 September 2008 (UTC)

Done. Linked to relaxation (physics) and tried to make lead as general as possible. It would be great for people to add in non-electronic examples. Diagrams of generic relaxation oscillators would be nice too. —TedPavlic (talk/contrib/@) 07:20, 30 December 2009 (UTC)

Diagram of classic relaxation oscillator[edit]

We need a diagram of the "classic" relaxation oscillator. Here is one in ASCII-Art, which may help. The symbols are poorly drawn, especially the neon bulb. Values are approximate; T ~ RC = 1 second (here) See also Pearson-Anson_effect.

 |---------|         Resistor, 100k
 | 200 V  +|---------\/\/\/--------+-----------|
 | DC      |                       |           |
 | supply  |         capacitor + ------      ( o )  neon bulb
 |         |         10uF        ------      ( o )
 |         |                       |           |
 |        -|-----------------------+-----------|
Okay. Added this fig and a link to Pearson–Anson effect. —TedPavlic (talk/contrib/@) 07:42, 30 December 2009 (UTC)
If you want to be pedantic, the classical relaxation oscillator does not use a 'neon' bulb as the discharge element. It used a spark gap (and thus required a high voltage to drive it). The really really classical relaxation oscillator required a Wimshurst machine (or similar), a Leyden jar or two and a spark gap. The resistor was inherent in the Wimshurst machine. (talk) 19:07, 5 August 2012 (UTC)

A simple relaxation oscillator may also be built from a 555 (wired as an inverting schmitt-trigger), and a single resistor/capacitor. Wiring is:

First, wire up an inverting schmitt-trigger from the 555.
 Pin 1 = Ground
 Pin 8 = Positive
 Pins 4,5,7 are left unconnected
 Pin 3 = Output.
 Pins 2,6 are connected together.
Then, connect the RC between pin 3 and ground, with pins 2,6 connected to the junction:
  PIN3 ----\/\/\/----PIN2,6----||-----GND
I will add this 555 example as an alternative to the comparator-based Schmitt trigger. —TedPavlic (talk/contrib/@) 07:46, 30 December 2009 (UTC)

Note: The "normal" 555 astable configuration (using pins 2,6,7, and having 2 resistors and a capacitor) is not a relaxation oscillator: it is more complex.

Hm. I think you are incorrect. See the generic definition of a relaxation oscillator. As long as the storage element is "almost always" (using terms from measure theory) dissipating, we have a relaxation oscillator. The element is always trying to get back to its equilibrium... It just happens to be perturbed on a measure zero set. It is true that sometimes it is discharging at a different rate than others, but it is always trying to get back to its equilibrium, and it dissipates to do it. —TedPavlic (talk/contrib/@) 07:46, 30 December 2009 (UTC)

Silly Choice[edit]

This article is made far less useful because all three resistors in the circuit are given identical values, R. Noodle snacks (talk) 11:35, 16 May 2009 (UTC)

Do you feel a different choice would communicate the concept of a relaxation oscillator better? It seems like a different choice would be better for, say, the Schmitt trigger page... not here. I think the point is communicated fine here. No? —TedPavlic (talk/contrib/@) 07:57, 30 December 2009 (UTC)

Does the op-amp oscillator fit the definition of a relaxation oscillator[edit]

The article states:

A relaxation oscillator is an oscillator in which a capacitor is charged gradually and then discharged rapidly.


The electrical output of a relaxation oscillator is always a sawtooth wave.

However, as long as VDD and VSS are symmetrical compared to ground, the op-amp oscillator's capacitor will charge and discharge at the same rate and the output will be a triangle wave.

Either the op-amp oscillator is not a relaxation oscillator or the relaxation oscillator needs to be redefined. Rsduhamel (talk) 22:06, 29 December 2009 (UTC)

Wow. The introduction of this page had some major errors. A relaxation oscillator certainly need to involve sawtooth waves (additionally, the operational amplifier circuit on the page at present does not generate sawtooths nor triangle waves -- it generates exponentials and square waves). I think things are fixed now. Please review. —TedPavlic (talk/contrib/@) 07:58, 30 December 2009 (UTC)