Sensor substitution

[ivconic]

Recently i got few FGM3 sensors. It was painfull to order,wait and finally get those all the way from UK. Also initial price "rised" until get here

So...I am having just few of those. Already performed few elementar tests using scope. Connected +5v and saw square 5v oscilogramm. When some magnetic metal closed to sensor frequency rising and vice versa, just as described in datasheet. Also amplitude changes a bit, depends of a side where magnetic item is placed. So..elementary i dug what is all about.
I want to simulate this particular sensor with some handmade.
Of course i do not expect very same preferences, would be satisfied even with closer results.
My question here is;
we do have some coil inside, what else FGM3 do have inside that package?
Some sort of oscillator? Amplifier?
Could it be a sort of parallel resonant LC oscillator?
Anybody have any idea?
Least i can do is to smash sensor carefully and see what is inside, yet i would like to void that, not so cheap and not for wasting just like that.

Any help?
I dont want to make copies and harm Speake's copyright rights. Just want to learn more and make my life more easier...

[ApBerg]

fmg-3

Hello Ivica.

On the Yahoo magnetometer site is more info, look at the photo's from jpopelish.

[ivconic]

Wow! This gives some picture!
Thanks much!
I can not approach to files there, i am not a member. Are there any more interesting files?
How to distinguish component values?
Anyway Thank you very much!
Any further information is more than welcome!
I was thinking to make my own sensor but to take FGM3 as starting point and further to experiment with EPE project. Also i do have my own ideas, but will discuss those later when experiment a bit more...
Regards!

[Atul Asthana]

Looks like the sensor is exactly like what is described in Don's article. The oscillator seems to be using the core in feedback mode.

[KORRIGAN]

fgm3

Hello ivonic here FGM3 the circuit with component values

[nahok]

Hi;

can make the value of coil will be great.

best regards.

[mrkhrdr]

Hello ivonic here FGM3 the circuit with component values

Well, the 2 schematics are not quite the same. Cap C9 is no big deal, just a large decoupling cap for the 5V supply coming over a line of indeterminate length an location. The placement of FB or TP, depending, is important if we want to reverse engineer the device. In Korrigan's drawing, TP taps the junction of Q1's base and C1. In the other, FB taps the junction between C1 and L2. If the latter were true, FB could be used to bias L2, perhaps adjust the balance between the 2 coils for zeroing out stray fields, improving linearity, correcting for temperature, whatever. I can see no use for TP other than a test point; for what purpose, I know not.
Otherwise, it seems that most of the circuit is an oscillator. Using the former schematic, I'd say that C1 is charged until the voltage at the base of Q1 switches the transistor on. Then, current flows through L1 to ground through R2,R3, and R4. The base of Q2 goes high, and it switches on, bringing Vout to ground (0). Presumably, C1 is also discharged through Q1 bringing down the potential at its base, and starting the cycle over again since this turns Q1 & Q2 off, bringing Vout up again. This creates an oscillating field around L1. I'm not sure what happens with L2. Presumably, current flows through it while C1 is charging and in the reverse direction when it is discharging? The x-ray seems to show that L1 and L2 are wound coaxially, which presumably allows the ambient magnetic field to be sensed, and perhaps couples them together like coils in a transformer. I really don't know. Any help would be much appreciated.

[Ethno]

This is the easiest magnetometer based on microcontroller PIC16F628A with sensors simi
lar to FGM-3. At the moment we are testing it. http://youtu.be/c7qvPFETYDk

[SimonS]

Hi to all
Mr. Bill Speake is dead and now is problem where to buy this sensors. I try to make it, but there is simple no information. I try to measure coil resistence (FB). FGM3 frim 3.sensors I got 3. diferent result. Same with FGM-1. It look there is not same number of turns. I have no idea why.
Have someone more information?

BR Simon

[kt315]

if i need to calculate number of turns of a transformer for example i reel off it on a bobbin,
then i reel up on the trasformer bobin back. i use a handy tool for DIY, with mechanical counter.
counter gives me sure number of turns.

[homefire]

I think it's working some what like this set up. http://motivationtolearn.org/wordpress/?p=1347

[SimonS]

No it is impossible just to reel off, becouse is everything in epoxy. Trying to get out you risk to cut it. And there is 2. coil at one base ...
@homefire it is little to big for carry it, but it is working staff for sure!

[Carl-NC]

Mr. Bill Speake is dead and now is problem where to buy this sensors.

I didn't know that, sorry to hear.

I think it's working some what like this set up. http://motivationtolearn.org/wordpress/?p=1347

The Speake sensor is a solenoidal winding, not toroidal.

[SimonS]

15.1.2017. I got note from his wife RIP!

[homefire]

I didn't know that, sorry to hear.



The Speake sensor is a solenoidal winding, not toroidal.

Yes but working some what the same. Magnetism producing frequency and Amplitude variations. In the FM-3 the internal ocs energized coil is some what the same.