Tesla's "COIL FOR ELECTRO-MAGNETS".

[TinselKoala]

Found that site : http://www.kerrywong.com/2010/10/16/avr-lc-meter-with-frequency-measurement/

but I'm not sure if that similar version is working good... although it has a nice feature of calibration.
TinselKoala, can you merge both circuits to prepare one able to measure frequency,inductance, capacitance and maybe also parallel tank circuit frequency (external RCL circuit with the method of kick into ring down oscillation and count peaks as you described in some video) ?
That would be really useful device !

The arduino inductance meter I showed in the video places a known capacitor in parallel with the unknown inductance under test, then "pings" this tank, senses its resonant (ringdown) frequency, and then applies some math to calculate the inductance based on the pre-programmed value of the known capacitance. The measured resonant frequency is already displayed for each "ping" on the LCD display.

With a little cleverness and a rotary switch, one could adapt the same circuitry easily to use a known inductor to test an unknown capacitance. And the math performed during the calculation can be "calibrated" by allowing a variable to be controlled externally, by a potentiometer for example, so that the system could be adjusted to read accurately on a known standard.

Here's the circuit schematic for the "front end" that makes the tank circuit, pings it, and reports back to the Arduino. The two capacitors are the tank caps and the position of the unknown inductor is shown. So I'm sure that the clever builders here can make a switch arrangement that used a known capacitor, a known inductor, and allowed switching back and forth, so the tank could be set up to measure either an unknown cap or unknown inductor. The process of ringing the tank and measuring the frequency is exactly the same, so the only mod to hardware is the rotary switch and the known components. Tweaking the Arduino code is also trivial, and adding the pot for calibration only a slight bit more complicated.

To measure frequency of an external system a stand-alone implementation would be better I think, using different functions (more accurate) in the Arduino to measure the frequency.

My Arduino code for the TKInductometer as shown in the video is here:
http://www.mediafire.com/?bps78nwtkp5nwnp

Please feel free to play around, improve, criticize, etc. I think I showed the original source where I got the basic sketch in the code comments.


ETA: Now that I see the schematic again, I recall that the comparator I used is a dual unit, two comparators on a single 8pin DIP. So you could use both, one for the inductometer and the other for the capacitometer. Then you'd need a bit more coding, but you could eliminate the need for the rotary switch, just have a board with the two functions running out of the same chip, and select which one to use in the software, with a button or something.

ETA2: I used all scavenged parts, from old TV chassis, so the cost of this meter is essentially zero. You have to factor in the cost of the Arduino and the battery and the optional LCD display, but they are used for so many different things that the marginal cost of them in this meter is only pennies. If you are building a stand-alone meter you'd use a different Arduino designed for permanent installation (cheaper and smaller but runs the exact same program) and the total cost of the meter would probably be about 60 or 65 dollars, half of which is the LCD display.

[forest]

Your circuit has the nice feature - it can measure resonant frequency of already assembled RC circuit while the circuit from the link I posted can measure precisely inductance,capacitance and frequency. Having all those functions in one device would be an advantage, but I can't imagine the switch needed for switching all those functions...
I think from your circuit can be taken the method of kicking resonant circuit while from the link I posted the measurement of frequency. What do you think ?


Ooops, sorry for off topic. IF there is interest in such meter I will start new thread

[TinselKoala]

Your circuit has the nice feature - it can measure resonant frequency of already assembled RC circuit while the circuit from the link I posted can measure precisely inductance,capacitance and frequency. Having all those functions in one device would be an advantage, but I can't imagine the switch needed for switching all those functions...
I think from your circuit can be taken the method of kicking resonant circuit while from the link I posted the measurement of frequency. What do you think ?


Ooops, sorry for off topic. IF there is interest in such meter I will start new thread

Actually, the schematic you posted is pretty much the whole thing. It uses a slightly different method to ring the tank to read L and C (switched by the switch on the left) and feeds this to another comparator, which can also be switched to read frequency directly, again using the same method of detecting zero-crossings of the applied signal. It's all there !
But the complex LCD driver and a lot of the program code is unnecessary if you use the simple and easy to use pre-wired Parallax LCD. It only needs three wires (two power, one data) and very simple code in the arduino to send data to it.

[gyulasun]

Hi Mags,

I remember a measurement on a single and a bifilarly wound air core solenoid coils, done by Nichelson, using a HP network analyser. See this PDF file: http://home.comcast.net/~onichelson/VOLTGN.pdf from his site: https://sites.google.com/site/teslanichelson/

Interestingly, he compares the quality factor, Q=X_L/R of the single and the bifilar coils and he calles the Q as voltage gain. His single wire coil (207.9 uH) gave a resonant frequency at 19 MHz with its own self-capacitance while the bifilarly wound coil (205 uH) gave him a resonant frequency at 11 MHz with its own self cap. This latter frequency shows that the series bifilar coil has a higher self capacitance than the single wire coil has because for the same number of turns and shape factor the bifilar coil has a much lower self resonant frequency than the single wire coil.

So he found that the calculated and measured voltage gains differ as many as 929%.  Practically the measured unloaded Q of the single and bifilar coils are involved and for applications that can preserve the high unloaded Q the bifilar wound coil seems to have advantage.
Nichelson also mentioned the bifilar coil in this paper too: http://home.comcast.net/~onichelson/Thermodynamics2.pdf  Page 6 and 7.  Quote from Page 6: "A bifilar coil is capable of holding more charge than a single wound coil. When operated at resonance, the distributed capacitance of the bifilar coil is able to overcome the counter force normal to coils, inductive reactance. It does not allow what Tesla described (Tesla, 1894) as the formation of 'false currents'. Because the electrical activity in the coil does not work against itself in the form of a counter-emf, the potential across the coil quickly builds to a high value."

I still have to understand and figure out how the high voltage gain can be utilized energy-wise in a bifilar coil? This is the same problem if you build a high Q LC tank circuit and try to preserve as high loaded Q as possible, to be able to access the circulating high current, no?  At resonance an LC circuit where the coil is say single wound, the counter force shown against  the AC input current is also absent, no?


For your recent coils, you could measure and calculate their self capacitances if you have a signal generator and a scope. (for signal generator a function gen or even a pulse gen made from the 555 timer could be used.)
Here are two links how the coils self resonant frequency measurement is done: http://www3.telus.net/chemelec/Calculators/Interwire-Coil-Capacitance-Calc.htm  and http://www.qsl.net/in3otd/inductors.html  The first link uses the coils self capacitance to get a parallel LC resonance while the second link uses two known capacitors to resonate the coils i.e. two caps for each coil. 

rgds,  Gyula

[gyulasun]

.... can you merge both circuits to prepare one able to measure frequency,inductance, capacitance and maybe also parallel tank circuit frequency (external RCL circuit with the method of kick into ring down oscillation and count peaks as you described in some video) ?
That would be really useful device !

Hi forest,

Albeit it costs USD 69 plus shipping, here is an ebay offer for such meter (frequency, inductance, capacitance and power 1 nW-1 W):
http://www.ebay.com/itm/Frequency-Counter-Micro-Power-Capacitance-Inductance-Meter-L-C-F-Cymometer-/181016599062?pt=LH_DefaultDomain_0&hash=item2a256e1a16

Gyula