Testing the TK Tar Baby

[picowatt]

TK,

How is it you were able to build, test, post, make videos, and take requests for measurements all at the same time?

Is there more than one of you?  Alien assistance?

PW

(and fix the Cav)

[picowatt]

@.99,

With the new "Altoids" circuit, how low were/are you able to get the DC bias current?

You might put a cap between the MOSFET source and gnd and then place various resistor values (1R to 20R) across the cap.

This would allow the AC gain to remain unchanged while adjusting Ibias with the resistor value.  May as well make the 9V last for as long as possible.  Possibly play with increasing the zener voltage as you vary the added resistor.

At some point, maybe an AD834 or similar should be assembled into an analog circuit to do the multiply and avg so a "fancy scope" is not needed to calculate the neg/pos mean.

PW

[TinselKoala]

Rosemary.... when you get your scope back I do hope you will learn to set the trigger properly. The reason the scope's display is unstable in the shot above (you had to stop it in mid-scan in order to make your screenshot) is because you have your trigger set improperly. Note the purple "T" on the right side of the screen, and the trigger setting in the box below the trace window. You are triggering on the purple trace.... but your trigger voltage level is set far outside that trace's voltage range. Thus the scope cannot trigger stably and the screen will be "jumpy"... JUST AS IT IS IN YOUR DEMO VIDEO as well. Many of your scope shots show a similar improper trigger setting.

In the future, try to use the trigger level knob to get that "T" down into the voltage range of the channel on which you wish to trigger.... usually the DRIVING signal since that is the most stable (blue, FG trace), or the signal with the highest CLEAN voltage level. The purple trace would have been OK if you had lowered the trigger level... the "T" position ... down into the actual voltage range of the signal you are asking the scope to use for its trigger. Then you can move the trigger point horizontally (in time) if you like, so that the displayed traces don't start right at the beginning of a block of oscillations, but have a "lead in" period first. The time where the scope triggers is displayed along the top of the trace window by the little purple triangle and the -62.000 ms figure. So the "place" where you are asking for a trigger is where this triangle, projected down,  and the "T" level, projected to the left, intersect. A place outside the envelope of your purple signal, hence the unstable screen display.

And you might find it interesting to RTFM:   Read The Fine Manual.... you just might learn something about using oscilloscopes properly. And acronyms, too.

[TinselKoala]

TK,

How is it you were able to build, test, post, make videos, and take requests for measurements all at the same time?

Is there more than one of you?  Alien assistance?

PW

(and fix the Cav)

You forgot mowing the three lawns once every four days, cooking the gourmet linguine dinners and making the Lissajous videos (a new one, using 4 oscillators, is up, if you have 20 minutes to waste). And cleaning up after three dogs and an Ainslie.

I still have a few trained gremlins left over from my A&P days. They help out as long as I give them a few drops of rum in their sugar-water now and then.

But you know... maybe there is more than one of me. Don't you ever wake up feeling tired, with some strange new circuit humming away on your workbench, not knowing how it got there?

[TinselKoala]

@.99,

With the new "Altoids" circuit, how low were/are you able to get the DC bias current?

You might put a cap between the MOSFET source and gnd and then place various resistor values (1R to 20R) across the cap.

This would allow the AC gain to remain unchanged while adjusting Ibias with the resistor value.  May as well make the 9V last for as long as possible.  Possibly play with increasing the zener voltage as you vary the added resistor.

At some point, maybe an AD834 or similar should be assembled into an analog circuit to do the multiply and avg so a "fancy scope" is not needed to calculate the neg/pos mean.

PW

Saaayy... do either of you  know anything about microprocessors? I have these Arduino clones with 16 and 32MHz Atmels in them,  and some other peripherals here... I'll bet it would be possible to program an Arduino to make the right frequency oscillations and interface its PWM output into an easily tunable little filter or pulseforming network that would light up an LED when OU was attained...... What do you think?

I've got some good opamps on hand but no AD834s.