Interesting Oscillator

[porkluvr]

Mr Pork said

Even the Paint program that comes with windows will let you paste the screen shot and save, but unfortunately you can't crop with it.

its called the "select" tool

I see. Paint can be made to work with a few more steps. I don't use it often enough to ever have figured that out. Thank you.

[mikebg]

Your oscillator circuits are not correct designed. Here is the original correct designed circuit:

[turtlebowl]

Your oscillator circuits are not correct designed. Here is the original correct designed circuit:

Mike what coil is that in your circuit drawing? And is the 1.5 ohm "sticky note' you added on the tx the bucking coil, combined TX coil or something else?

[mikebg]

Mike what coil is that in your circuit drawing? And is the 1.5 ohm "sticky note' you added on the tx the bucking coil, combined TX coil or something else?

Most old coils of White's have equivalent capacitance of TX tank circuit 1uF (two or three capacitors in parallel) and equivalent resistance 1.5 ohm. This is the resistance of series connection of main TX coil and the bucking TX coil. According White's terminology, the bucking coil is named "feedback" winding. I have no information for new coils of White's.

[simonbaker]

Hi Maurice try this puppy its a real bruiser!

I got the existing IGSL osc to fire into a complmentary mosfet pair feeding a resonant cct.

1A pk to pk.

Madness.

S

Looks interesting, I'm bookmarking for reference.

I'm wondering about the "4-pole" tank -- a fair amount of power is dissipated in the non-search coil (4.5 mH 3 ohm), and I wonder if there is a way to get as high current in the search coil without the auxiliary coil.

Interestingly the currents in the two coils seem to be in phase -- it would be wickedly cool if somehow both coils could be used for the search coil, by center-tapping a single coil and adding on the capacitors. But the mutual inductance would change the whole equation -- still, there is some non-mutual inductance that might be configured appropriately.

Edit: the currents are really opposite in phase if you use overall circuit loop direction, so probably the above idea is not feasible whatsoever. However, perhaps could be useful for a dual-coil anti-phase search head design...

Something to play with in Spice.

-SB

[golfnut]

Hi, th series cap is a dc block.#
The series L is a match component - the value will come down to a std value with little overall power change.

Resistance is pesimistic in the model, in reality its easy to source 4.2mH with R<0.2ohms

e.g.

Technical/Catalog Information ELF-18N020A
Vendor Panasonic - ECG
Category Filters
Inductance 4.2mH
Impedance -
DC Resistance (DCR) 130 mOhm
Current 2A

I reckon you could do away with the resonant nature of the Tx and use a complimentary MOS pair to simply bash bash into a coil - at a rate defined by the user, or a range of pulse rates cycling around randomly.

Steve

[golfnut]

My next foray may be be a PI using a CDI for a pit bike they are only £3 on the bay.

S

[DOOLEY]

hello golfnut ,

there is a possibility that the cdi unit has a buit in rev limit of about 8000 to 10000 rpm ,
divide that by 60 to get it into herts and it will cut out when driven above 133 hz or poss 166 hz respectivly , or there abouts ,

nice idea to get the voltage , but not much amperage there , don't want to be negative ,
worth a go , only poss have to stick saftley below rev limiter.

[mikebg]

Here is an explanation how self-bias of circuit diagram in post #32 works:
The attached image is equivalent curcuit diagram for calculation of timeconstants.
The emitter junction of Q2 operates as a diode charging C21 with showed below polarity. The voltage is proportional to amplitude of oscillation. The charging timeconstant is more than R10 x C21. It is increased because the resistance of resistor R10 appears increased about 100 times (parameter Hfe of Q2). The discharging timeconstant is R9 x C21 ie 1M x 2.2n = 2.2ms.
ATTENTION: The circuit can not operate correct with increased supply voltage, because the emitter junction of Q2 is as Zener diode. When the amplitude of oscillation exceedes its breakdown voltage, the self-bias can not stabilize amplitude of oscillation.

[golfnut]

Fair cop on the repetition rate... bit slow at 166 clicks

nice idea to get the voltage , but not much amperage there

The current would be ok though, these units drive an ignition coil primary, with a decent current and high di/dt

Its the ignition coil secondary that has the 20kv and small current..

S

[DOOLEY]

ah , i see,i was thinking of the all in one coil and driver cdi units used on most modern small engines,so you intend using the seperate cdi unit ( no ign coil) to turn on and off you coil,i'm with you now.

[golfnut]

Yeah, bit like this..
I could solve rep rate issue by having 3 cdi's each driving a seperate coil! fire threee in sequence. Biff bam wallop

http://imageshack.us/photo/my-images...iagramtx8.png/

[DOOLEY]

hello golfnut ,

not sure if the cdi units will be an advantage.

cdi (capacitor discharge ignition) is just a voltage multiplier charging a capacitor and a mosfet discharging it to a coil when triggered by the crank sensor , with the ability to advance the timing as the rpm goes up,

so , timing may not be uS stable , may vary a little , and added to that there is a cut off frequency for engine protection , so at some point it will deliberatly stop at a set frequency.

originaly a trigger (usualy magnetic or optical) opperated a mosfet or transistor which in turn sent battery voltage to coil on and off.

but this was limited to whatever battery voltage was on the vehicle , so a multiplier was used to charge a capacitor then the mosfet would send to coil ,resulted in a better spark and smaller coils could be used.

fail to see the advantage with this idea , we cant magic power from thin air , either we increace the amperage to a coil or increace the voltage to a coil , both cost battery power , so a cdi unit raising say 12v to say 24v then sending to a coil still costs us power.

same could be done with discrete components.
but to double the voltage costs us double the amperage + conversion losses=still lost.

[golfnut]

Generating a good thump of current thru a coil is non trivial ur right.

Turning a fet off is a good intro, but its a bit lame - its not much further than the first thing you would think of.


To get a coil to do things quickly they need a good kick. Like -300v makes them sit up and conduct sharpish. CDi units do this for U.

A guy from oregon eluded that there are moves coming like the above. If I have read between the lines correctly it would be worth £3 to disprove it all as you say!

S

[MAURICE]

Re - take on oscillator

HI.
I have been doing a little experimenting looking for a oscillator for setting up coils.
I built circuit from Russian site it is posted in coils section.
I could not get it to work.
I have just finished this oscillator from this post on veroboard and it works well.
Checked TX coil +- 1.43mH C= 100nf F= +- 13.3 kHz.
RX coil +- 17.38mH C= 6.6nF 28 ohms F= +- 14.6 kHz.
An additional coil I had lying around
+- 6mH C= 10nF F=16kHz.
It works well with these coils which represent a fair spread ( even with 6 volt supply).
Also very simple layout.
Best Regards
Maurice.