Hall effect detector

[daverave]

if the mosfet and sample switch is bypassed will the surf pi dectect iron at good depth or just a few inches ????

[Waikiki_Sweep]

Only big chunks that have its own magnetic field. But I have checked that if you put strong magnet in the center of the coil it will detect bottle caps and hair pins too at 4-6 inches. Probably it is possible to increase depth with amplification of signal. But it is not practical to keep magnet in the coil. I already have crazy strong huge 72 lbs pull neodymium magnet in my stainless steel scoop. If I put a coil around it I will have a magnetometer to detect iron.

[daverave]

im just about to fill my coil housing with resin but i just did a capacitance check with my meter across the coil and on the 20nf setting the meter wont read and shows 1 which i guess is over range...it will only show a reading in the uf range at approx 10.5 uf surely this cannot be correct...my coil is 18 turns of 30swg copper wire...5 ohm resistance....i used one layer of spiral wrap and on top is wound scotch 24 screening all around the spiral wrap apart from a gap of about 2 inches....can anyone advise cause i dont want to resin this coil if i have done something incorrect which shows high capacitance reading....the meter is a cheap one from ebay china.

[WM6]

This way (with C-Meter connected across the coil) you cannot measure parasitic capacitance of the coil.

This way you can measure inductance only, but with L-meter and not with C-meter.

For parasitic capacitance you need to know resonating frequency of the coil and inductance and resistance of coil, then calculate parasitic capacitance out of this.

[daverave]

im not sure how to calculate those parameters you mentioned...to get the frequency of the coil i guess i would need a frequency generator which i dont have...im going to friends garden tomorrow to fill coil with resin...i bought some black dye also but not sure how much to mix with resin....im dreading it !!!

[Waikiki_Sweep]

im not sure how to calculate those parameters you mentioned...to get the frequency of the coil i guess i would need a frequency generator which i dont have...im going to friends garden tomorrow to fill coil with resin...i bought some black dye also but not sure how much to mix with resin....im dreading it !!!

At least you can measure capacitance between coil and shield. Interesting who has what results in it?

[davros]

i have played around with the hall effect ic great idea ...how about hooking it up to a Lm311

I used this circuit for motor control the out put of the lm311 is a digital signal///you can view the out put on a scope or use an led ....it would be a square wave ,perhaps hooking your 2 hall effect ic's circuit up to one side of a bistable circuit the other to 555 audio oscillator out put of that to a amp every time the hall effect detected metal iron steel it would trigger the bistable and you would hear the signal ..bit easier than looking at a multi meter.

[Koala]

Always amazes me that the small sensor in my mobile phone picks up the magnet field of the earth. Better still if I watch the compass and walking down the pavement I can see the needle deflect when 8 foot from a lamppost and if there is a mild geomagnetic storm it spins all over the place.

[Waikiki_Sweep]

Unfortunately I did not get any decent range from A1301 sensors.
But this idea about digital compass looks promising.

For only $2-3 you can buy on eBay "HMC5883L 3 Axis Electronic Compass Magnetometer Sensor Module 3V-5V For Arduino"



and for $7 small Arduino board "Mini USB Nano V3.0 ATmega328" or "Leonardo Pro Micro ATmega32U4"



to build compact, smart and sensitive magnetic field sensing device.

[Koala]

I am no expert and not sure but will it only find iron?

[Koala]

just done a quick test with my phone. I start compass on my phone and fetch a large lump of brass up to phone 90 degrees to north no deflection same with aluminum. However with a small pair of side cutters the needle has an easy visible movement at over well 6"

[greylourie]

just done a quick test with my phone. I start compass on my phone and fetch a large lump of brass up to phone 90 degrees to north no deflection same with aluminum. However with a small pair of side cutters the needle has an easy visible movement at over well 6"

That is a good response..

[Waikiki_Sweep]

Probably that brass has a iron core inside. Also side cutters may contain remaining magnetism. Only object that has own magnetic field or capable to disturb Earth magnetic field will move compass needdle.
If you put strong magnet at some distance from the compass you will see it reacting on movement near that setup even much smaller objects like beer cap or hair pin.

[Koala]

Brass has no response.

Haven't found any iron object it can't detect.
Tried rusty old nails found from a beach
cycle forks
rusty strap of metal
bottle caps
large rusty nut

all give give good results. None round objects seem to give a better response but that could be just luck with such a small selection of targets. Bottle caps give the worst response but they are very thin.

[Koala]

found a nice free android app "Physics Toolbox Magnetometer" shows the 3 axis and you can zoom in and record the trace.