Simplest possible oscillator (with some constraints)

Question

I'm interested in finding an oscillator circuit that meets the following constraints:

Why do I care about these constraints? I'm a weirdo. (Sinusoids are "prosaic". Inductors are "messy". 2 transistors is "cheating".)

I found this, but is there something even simpler? (I think this is a sinusoidal oscillator anyway.)

To put it more politely, the reasons you give for your requirements are not engineering reasons. So you are not asking about engineering, you are just making up a puzzle. — The Photon, Aug 18 '14 at 02:33
:-/ It's more than just a musing. I want to build one, and it would be a useful stepping-off point for building more complex circuits. — MackTuesday, Aug 18 '14 at 02:33
This question appears to be off-topic because a complete circuit is required. — Leon Heller, Aug 18 '14 at 06:10
Where in the help section does it say a complete circuit request is off-topic? If you guys are going to be picky, you need to put a warning in your help section reading, "Warning: We're Picky". Don't have a help section that pretends to be inviting if the rest of you aren't going to be. — MackTuesday, Aug 18 '14 at 15:06
Simple circuit revisions or suggestions are certainly possible, but complete circuits or schematics aren't going to be something that *volunteers* will readily supply. — JYelton, Aug 19 '14 at 22:49

score 3 · Answer 1 · answered Aug 18 '14 at 02:45

3

Probably everyone knows about this 3-component oscillator- but it's hardly suitable for any serious application.

schematic

^{simulate this circuit – Schematic created using CircuitLab}

answered Aug 18 '14 at 02:45

Spehro Pefhany

I'm guessing that the cap charges, Q1 reaches the threshold voltage, and then it discharges, repeat. My question is how? Since current can't flow out of the base, I can understand it temporarily turning on, but then the base voltage would rise until it gets to 15-Veb. I'm obviously missing some trick with this setup. – horta Aug 18 '14 at 04:06
1

@horta it's not really a trick- the EB junction will typically avalanche (reverse breakdown is usually around 9V) and give you an sawtooth at the capacitor. It's like using undocumented op codes - not a great idea except for entertainment purposes. Breaking down that junction also degrades the forward beta of the transistor so throw it away afterwards. – Spehro Pefhany Aug 18 '14 at 04:18
It is called a Esaki oscillator after its inventor Leona Esaki – jippie Aug 18 '14 at 05:32
@jippie I only see one non-tunnel-diode reference to that name, and it's another jippie post on ese. – Spehro Pefhany Aug 18 '14 at 14:35

score 1 · Accepted Answer · answered Aug 18 '14 at 11:58

1

How about a unijunction (relaxation) oscillator e.g. 2N2646 enter image description here

answered Aug 18 '14 at 11:58

JIm Dearden

2 Answers2