Gaussmeter project

[-Elepro-]

hello,

here's my project....
range: 1730 north - 1650 south (with allegro A1302 hall sensor)
sensivity calibration (for use other sensor) from 0.250 mV/G to 6 mV/G
peak hold mode
auto zero set
10 bit A/D
programmed IC euro 30 (worldwide shipping included)

video

[-Elepro-]

bye

[salvarsan]

here's my project....
range: 1730 north - 1650 south (with allegro A1302 hall sensor)
sensivity calibration (for use other sensor) from 0.250 mV/G to 6 mV/G
hold peak mode
auto zero set
10 bit A/D

Nice execution.

The peak hold mode is an excellent feature.


What sort of battery life do you get?

Using the A1302, the limiting gauss should be +/- 1925G in increments of 4G.

Any idea why that's not happening?

FWIW, I've cobbled up a similar project using an Arduino.
Ideally, we'd have a 12 bit A/D for this one.

-drh

[-Elepro-]

Nice execution.

The peak hold mode is an excellent feature.

thanks

What sort of battery life do you get?


with my display (white character does not allow backlight off) current consumption is 16mA with dimmer and 20mA with full light.... if you use a display with black character you can switch off backlight... alkaline 9v battery is 500mAh and more.....


Using the A1302, the limiting gauss should be +/- 1925G



read well datasheet vout is min 0,25 and max 4,7 ..... my gaussmeter has 5% and 93% limits.... out of these limits display shown "out of range"
with ad22151 limits should be +/-5000 gauss but with worse resolution


in increments of 4G.

my firmware has a "kind of oversample"- for every value displaied there are 1024 sample in normal mode and 64 in peak hold mode.... then... watch this video (excuse out of focus)...display shown 0-1-2-3-4-5-6 gauss

excuse for my bad english

[-Elepro-]

Ideally, we'd have a 12 bit A/D for this one.

-drh

i see now arduino boards.... all have 10 bit ADC

[-Elepro-]

a clarification for who contact me with PM


i don't sell kit because i have not way to make it...
i sell only the programmed integrated circuit with my software on it...

all other parts are available everywhere for about 15 euro (lcd included)...
....pcb is so simple that it is possible to build with a pcb pen (i can explain how) or with press-n-peel technique


bye

[MKB]

Excellent looking project, PIC's are amazing versatile devices. However, if you ever issue a revision, I'd suggest replacing the 7805 with a stepdown switching regulator, or use four cells with the circuit. You're losing a lot of 9V battery life to heat with the 7805.

Do you have a method of performing an absolute calibration of the meter? Is there a standard calibration magnet available? Or is the hall effect sold as a pre-calibrated part? I built a gaussmeter using a Melexis linear hall effect and a panel meter, and it works well, but do not know if it is anywhere near calibrated or not.

[Joe Gwinn]

a clarification for who contact me with PM


i don't sell kit because i have not way to make it...
i sell only the programmed integrated circuit with my software on it...

all other parts are available everywhere for about 15 euro
....pcb is so simple that it is possible to build with a pcb pen (i can explain how) or with press-n-peel technique

You will sell far more units if you put complete kits together.

It's a real nuisance and expense for your customers to buy one of this and one of that, while you can buy 50 of this and 50 of that and assemble the kits for very little per part. As for the PCB, again making one is a big nuisance for your customers. There are multiple companies in the US that will make good PCBs in small quantities for you, and if you order 50 it gets pretty cheap. Given that you price in Euros, I assume you are in Europe. I would assume that there are PCB houses in Europe as well. In the US, the board houses advertise in the back pages of electrical engineering trade magazines like EDN and EET as providing prototype boards.

There are lots of one-man shops developing and selling kits for various purposes, so there must be reasonable money in it.

[-Elepro-]

I'd suggest replacing the 7805 with a stepdown switching regulator,

current consumption (especially witout lcd backlight) is very low.... power dissipation too
7805 is inexpensive and has noise and ripple free output.... important for adc and sensor supply

Do you have a method of performing an absolute calibration of the meter? Is there a standard calibration magnet available?

i do not sell meter ..... who build my meter can performing perfect calibration comparing it with another meter or a reference magnet or can Put their trust in sensor quality

Or is the hall effect sold as a pre-calibrated part?

allegro a1302 is uncalibrated.... but with my meter you can use any other sensor (sensivity from 0.250 to 6 mv/gauss) you must only set it in calibration menu


I built a gaussmeter using a Melexis linear hall effect and a panel meter, and it works well, but do not know if it is anywhere near calibrated or not.

melexis produce a very cool sensor mlx90215... but they do not issue programming specs and i won't buy their programmer.... other their sensor i think are uncalibrated....

bye

[-Elepro-]

You will sell far more units if you put complete kits together.

It's a real nuisance and expense for your customers to buy one of this and one of that, while you can buy 50 of this and 50 of that and assemble the kits for very little per part. As for the PCB, again making one is a big nuisance for your customers. There are multiple companies in the US that will make good PCBs in small quantities for you, and if you order 50 it gets pretty cheap. Given that you price in Euros, I assume you are in Europe. I would assume that there are PCB houses in Europe as well. In the US, the board houses advertise in the back pages of electrical engineering trade magazines like EDN and EET as providing prototype boards.

There are lots of one-man shops developing and selling kits for various purposes, so there must be reasonable money in it.

hi Joe,

you are right but i can't at this moment... but if anyone would do this i can offer programmed microcontrollers with a good discount rate

for the moment as required by PM in my next post i'll give a detailed parts list and info on the pcb build....

bye

[-Elepro-]

here's list....


R1 - 10 kohm trimmer
R2 - 5.6Kohm 1/4 watt
R3 - 47ohm 1/4 watt (you can increase this value for decrease backlight intensity and have a more long life battery)
R4- 1Kohm 1/4 watt (this is for backlight dimmer)

C1 - 330nF polyester
C2 - 100nF polyester
C3 - 100nF polyester
C4 - 100nF polyester (this is in the probe near sensor... watch photo...)

D1 - 1N4001 (or 02 03 04 05 06 07... is only for polarity inversion protection)

IC1 - 7805T (5 volt voltage regulator)
IC2 - A1302 (hall sensor)
IC3 - PIC16F883 (microcontroller...... needs my software on it)

1 X HD44780 compatible 16X2 (16 character X 2 row) lcd display (with positive voltage contrast)

2 X - normally open push button
2 X - SPST switch
1 X - DIL28 narrow socket (for IC3)

1 X 9volt battery clip

conn 1-2-3-4-6 - any 90° 2.54mm pitch connector (or you can solder wire directly in the pcb )
conn5 - you can realize it with pin header (soldered to display) and 1/2 DIL32 ic sochet (soldered to pcb)


________________________________________________________ _______

about trimmer and capacitor dimension, it would be better to realize first pcb so you can try them on it (anyway all have 5.08mm pitch)
trimmer must have regolation on bottom too (the pcb have a hole under it.... trimmer must be set from rear of the pcb because on top will be display.... watch pcb render image)

about display, i buoght this .... but you can buy any other similar hd44780 16X2 compatible with same dimension and positive voltage contrast (you can ask me)
if you buy display with black characters ( black on green) you will can turn off backlight (then circuit does not required R4 1Kohm dimmer resistor).... instead display with white character always needs backlight (and you have make dimmer with R4 1K resistor)

my suggestion is to try to realize pcb first....
in my next post i explain two simple way

bye

[-Elepro-]

here's pdf for pcb.... print it with 100% dimensions!!!!

expert can make pcb with photo_etching technique or cnc milling (i can issue gcode for this )

all can make pcb easily using these method:

- press-n-peel method - i don't explain.... you can search on youtube or google... link


otherwise you can obtain pcb following next steps (it will not wonderful but.... )

- print pdf and cut a board image (photo-etching image)
- attach it on copper clad board with double-sided tape
- make holes (don't forget mounting screw holes and trimmer regolation hole)
- remove paper
- with great pacience copy trace (with the help of holes) with a permanent pen
- put board in ferric chloride
- clean trace with thinner


bye

[firewire]

Parts

Thanks, -Elepro-
Now that's pretty cool!!!
Anyone up for making a mouser parts list?
Then we all can kinda order are own kit!!!

[firewire]

Parts list.

Here is what I have so far. After the = is Mouser part #.
I could not find 330nF E-Bay -
The DIL28 (for ic3) but could if your good! go with out the socket solder directly to the board?

R1 - 10 kohm trimmer = 858-38PKABR10KLF30
R2 - 5.6Kohm 1/4 watt = 291-5.6K-RC
R3 - 47ohm 1/4 watt = 291-47-RC
R4- 1Kohm 1/4 watt = 291-1K-RC

C1 - 330nF polyester = 594-2222-367-12334 NON in stock.
C2 - 100nF polyester = 594-222236525104
C3 - 100nF polyester = 594-222236525104
C4 - 100nF polyester = 594-222236525104

D1 - 1N4001 = 625-1N4001-E3/54

IC1 - 7805T = 512-KA78T05TU
IC2 - A1302 = 621-AH337-PL-A
IC3 - PIC16F883 (microcontroller...... needs my software on it)

1 X HD44780 compatible 16X2 = 696-LCM-S01602DSRA (Think this will work?)

2 X - normally open push button = 633-SB4011NOH-RO
2 X - SPST switch = 1055-TA2120-EVX
1 X - DIL28 narrow socket (for IC3) =????=Socket for IC2

1 X 9volt battery clip

Anyone like to double check my parts!?!?!?!?

Thanks,

[-Elepro-]

trimmer is too big....

never solder microcontroller

hall sensor in your list is a switch .... the only one linear hall sensor they have has 2,5mV/G.... then you could measure max about +/- 800 gauss ....

c4 is better small because must fit in the probe

here's my list.... it is not complete and checked yet....

http://www.mouser.com/ProjectManager...sID=2c947e7457