Oso Stat

Motocross Hour Acquisition/Logging/Tracking System

EMF Meter

Posted by Taylor Bernard on May 1, 2013


got it all built out, and remote with a battery pack.
im using same code and same amount of LED's guy with bargraph is, and when he's walking around he's getting way more variance in input amounts than i am.
only thing i can think of is that my antennae design isnt as good as his (or different), but i'm using a 5" piece of solid copper wire from romex so i dont know.

also, popped spark plug cap off plug and kicked bike over, and its not showing any reading.
couple things i'm thinking at this point....

1. stator is putting out DC (obviously) and maybe the arduino input can only recognize AC. this may work to our benefit if thats the case since 90% of electronics are AC and can filter those out.
2. CDI is somehow encapsulated to not let any EMF bleed out, this is unlikely though i think.

Comments

Justin Bernard on May 1, 2013:

nice, good work.  it could be that its not firing enough to register @ cdi unless bike starts and has consistent flow?

Justin Bernard on May 1, 2013:


not directly related, but remember i was mentioning resistor spark plugs a couple weeks ago:
http://www.ehow.com/info_12200287_resistor-vs-nonresistor-spark-plugs-atv.html

Justin Bernard on May 1, 2013:

basic explanation of what a cdi does.  apparently that is where the voltage is going from 10 to 40,000. i was thinking there was some sort of coil doing it between cdi and plug.  therefore should be getting emf off cdi comparable to at plug wire.
http://wiki.answers.com/Q/What_does_a_CDI_unit_do

Justin Bernard on May 1, 2013:

lolz.  tesla basically invented the idea of a CDI in 1897:

"In U.S. patent #609250 first filed February 17, 1897, Tesla writes 'Any suitable moving portion of the apparatus is caused to mechanically control the charging of a condenser and its discharge through a circuit in inductive relation to a secondary circuit leading to the terminals between which the discharge is to occur, so that at the desired intervals the condenser may be discharged through its circuit and induce in the other circuit a current of high potential which produces the desired discharge."

Taylor Bernard on May 1, 2013:

An EMF meter can measure AC electromagnetic fields, which are usually
emitted from man-made sources such as electrical wiring, while gaussmeters or magnetometers measure DC fields, which occur naturally in Earth's geomagnetic field and are emitted from other sources where direct current is present.

Justin Bernard on May 1, 2013:

crud crud.

can we build a magnetometer?

Justin Bernard on May 1, 2013:

http://www.geocomputing.co.uk/getpage.php?type=page&page=ppcmagnetest

https://www.sparkfun.com/tutorials/301

Taylor Bernard on May 1, 2013:

think maybe gaussmeter will suit better.

Justin Bernard on May 1, 2013:

http://arduining.com/2012/07/17/arduino-hall-effect-sensor-gaussmeter/

Taylor Bernard on May 2, 2013:

reading more on the CDI boxes, hard to find info, but looks like theres a mix of both AC and DC in the whole atv, street bike, mx world.
Theres a guy selling 100w stator coils on kxriders forums and i think his spits out both AC and DC on diff lines,
i want to say any accessories like headlight, radio, ect is 99%  of the time AC.

so maybe all mx bikes come with plain DC and if you want stuff like headlights, ect then thats why you buy a new magneto/stator. to get that AC option.

still reading...

Taylor Bernard on May 2, 2013:

ok im wrong. looks like magento/alternator puts out AC, then it goes to a rectifier, and that converts ac to dc. rectifier is the little matchbox sized piece of gear with fins in it in the wiring loop.
heres a zeeltronic cr250 diagram to see how things are wired

http://www.zeeltronic.com/manuals/CR250R_wiring_PDCI-11VT.pdf

Taylor Bernard on May 2, 2013:

hmmm.... looks like the CDI may be low to moderate power after all and not put off as much emf as we thought. power comes from magneto, to rectifier to convert to DC, then to the cdi which does the advance/retard of spark based on rpm and tps. then signal gets sent out to the IGNITION COIL then that is what stores power for a few ms then burst pulses it.


i'm going to try and tweak this code on the arduino to pick up better, then try a few more spots on the bike to measure from.

Taylor Bernard on May 2, 2013:

now the issue is proximity.
i dont think any of this stuff is putting out enough EMF or readable current that will work for us that far away (triple tree or frame area). if it stuck on TOP of the coil or cdi maybe.

look at this video how close guy has to get with a magnet to trip it.
http://vimeo.com/21847015