Testing the TK Tar Baby

[poynt99]

Just a FYI TK, in case you were not aware;

In most of the scope shots Rosemary posted, the HV oscillation trace is from the high side of the load resistor, rather than directly off the Drains.

The wave form might look a little different there (in amplitude anyway). That's where I always measure in the sims in order to match what the posted results are.

Just something you might want to try.

[TinselKoala]

I figure the very best way to..."prevent" the NERDs from using the very simplest 555 timer that I used is to post the schematic someplace where she won't be able to find it. Like on the internet.

That way, if she ever does decide to test she will never be able to bring herself to use something I came up with, and she'll waste tons of time trying to develop her own timer.

I kind of like this role she's cast me in... the evil Debunker in his bunker, debunking bunkum with reverse-engineered bunk.

(ETA: I forgot to put the pot value on the schematic. It is a 100K trimpot.)

(ETA 2: GL noted that I should have indicated the "-10V" supply point as "0 V". The notation I used is  misleading because it usually refers to a bipolar supply and that isn't what is intended here. Think "9 volt battery" and work up from there. Sorry if there was any confusion....)

[TinselKoala]

Just a FYI TK, in case you were not aware;

In most of the scope shots Rosemary posted, the HV oscillation trace is from the high side of the load resistor, rather than directly off the Drains.

The wave form might look a little different there (in amplitude anyway). That's where I always measure in the sims in order to match what the posted results are.

Just something you might want to try.

Ahh...I wrote a nice long answer to this then the forum ate it.
The high side of the load is the "battery" trace in her data, isn't it? I've found that this doesn't give me as much info on my setup as the common drain trace does (the transistor side of the load). The circuit is so sensitive to inductances that even moving the probe ground lead from the negative rail on the board, over about ten inches to the negative battery terminal itself, makes a big difference in what features I can see and how stable the feedback state is.
(What's neat is at low amplitude the feedback is an almost perfect sine wave !)
The NERDs show the drain trace in the video, and should have shown it in the paper data too.
The probes in the center of the board here are on the common drains, I believe.
But yes, sure, when I have the Tek DSO to play with I'll look at the high side of the load too, and other places. It's just that my analog scope and all these wires make the "battery" trace useless to me.

[Groundloop]

I figure the very best way to..."prevent" the NERDs from using the very simplest 555 timer that I used is to post the schematic someplace where she won't be able to find it. Like on the internet.

That way, if she ever does decide to test she will never be able to bring herself to use something I came up with, and she'll waste tons of time trying to develop her own timer.

I kind of like this role she's cast me in... the evil Debunker in his bunker, debunking bunkum with reverse-engineered bunk.

TK,

Where did you put the current return path for your +10 / -10 Volt power supply for the 555 circuit?

GL.

[TinselKoala]

TK,

Where did you put the current return path for your +10 / -10 Volt power supply for the 555 circuit?

GL.

Oh sorry, you are thinking it's a bipolar supply like for an op amp? My bad, I guess I didn't make it clear. It's just a single 10 volt supply, the positive to the +10V and the negative to the -10 V. I guess I should have labelled it +10 and 0, or something. Sorry about the confusion, it has been a rather long weekend.  Obviously, whatever supply you use must be kept floating wrt the main circuit, or I dunno what will happen.

A fresh nine-volt battery will work fine but won't be as stable as a regulated power supply. The circuit starts working at about 5 volts, continues to increase osc amplitudes until about 12 volts, and lets the magic smoke out of the 555 at around 15-16 volts. I used a small heatsink on the 555 and it helps the stability a bit, I think.

(Thanks.. I really should correct the diagrams, and I will, but a bit later on, I'm pretty pooped right now.)