AVR Freaks

jgmdesign , you are right, and I apologize to the Ross, too. Just measured two chokes with result:

1.4ohm L=.03H  (27uH)
1.8ohm L=.05H  (47uH)

Sorry to blame innocent EB product, really.

I think I just (re)posted this image a week or two ago...

This was from one of my son's classes a few years ago.

They had to make their own coil of whatever-the-value-was.

We fed the RC circuit with a (slow) square wave, (Baseline offset to 0V, so not a bi-polar signal).

Then we measured the RC time constant, Tau.

When the voltage drops to 36.8% of its original value, you measure the time for that to happen.

L = Tau * R

Easy.

The scope shows a few of our his coils, and a line across the scope at 36.8 % of the Vmax.

(I think that line was the second channel trace, IIRC)

That made it easy to read the time, and calculate the L.

Photos, always a challenge these days, will follow.

JC

Interestingly I was looking for LC oscillator circuits and (on an 90s style Russian site) found one that can be viewed as an "auto-tuned" bridge:

I redrawn it to make it clearer that it is a bridge

The way I interpret this, the opamp tries to balance the bridge by making the circuit oscillate at such a frequency that the LC circuit has 10k impedance to maintain the impedance ratio on both sides (this will happen close to resonance, where impedance is theoretically infinite).

Anyway, if you know C and measure the frequency it should be easy to calculate L.

I haven't tested this circuit (yet) but I want to - more work for the AVR-DB opamps 

But of course since the OP has a signal generator, a frequency sweep should allow the resonance frequency to be found as previously noted.

avrcandies, this circuit also requires double power supply, 2x6 or more V. Agree with El Tangas, it is interesting one. The diodes- do not mind, any two 1N4148 can do it. Cap 1 is usually 330-1000 pF, try the most accurate one. Pot of 100K, resistors of 100K, do put cap blocking in + and - pins.

Remember those articles, the lamp was tiny 3V 50mA type. Not remember Nyquist, that was for the HF oscillations.

And, the real reason why "to linearize" may be that such circuits, when used as signal generator does needs to produce constant amplitude at output. For, example, make cap variable, then, normally the amplitude will not be linear from min to max, unless linearized.

not sure if they were the first to use this

Not the first, but their signal generator was the perfect one, and, as you said the HP started with this product.

The moral is: all we do should be perfect, as much as possible.

And your SG, does it have 100kHz, do you progressing- tell us what you did last days.