Vision of Arduino MAG

[bernte_one]

last night i had a vison of a Arduino MAG

i played with a simpled circuit called arduin emf detector

i the code you read out the voltage which is intruduced by a smal antenna into one analog input of arduino
and set the measured voltage in relation to an output signal for example pin13 led

for a simple differential magnetometer
i had this idea:

two ferrite core coil placed on one axis
both coils get one (same) connections to gnd of arduino
and each a single connectiond to one analog input of arduino

the measured voltage should in normal level nearly the same
if the voltage of one coil is higher or lower than the other a led should blink

thats the principle

[Krzysztof]

I think that the Arduino is is slow ADC. Not quite accurately.
The Arduino is fast enough for digital. Compare 2 digital sensors!
Best regards. Chris

[bernte_one]

an arduino question:

if i have a a big induction coil the current which is induced by the earth magnetic field is an alternating current (AC) so it would harm the arduino

if i want to meausre AC and dont loose sensivity should i use a rectifier or cut positive half-wave by diodes or something else

[Krzysztof]

Hi.
In each coil, even the largest, induces a current just by changing the magnetic field.
In time to change the current changes. With a fixed coil, changes in the Earth will be so slow that nothing you face.
While navigating the coil will keep track of the current changes in the substrate.
In any case, you face a lot of unnecessary EMI.
Best regards Chris.

[sled]

here's a good article about a DIY sensor:

http://www.geotech1.com/forums/attac...3&d=1149006588

the expected AC voltage is about 2.5Vpp for the first sensor variant - if you have a 5V tolerant arduino you could just use an op-amp to offset the DC level of the AC signal to Vcc/2.







Source: http://www.paulmonigatti.com/2011/09...crocontroller/

So if the signal is 2.5Vpp and Vcc=5V the voltage on the ADC pin will swing from 1.25V to 3.75V which is no problem for the arduino and you still got some headroom. Rf can be set equal to Ri so the op amp works at unity gain. Clamping diodes may be helpful too - just in case.

The frequency could be measured with the integrated comparators, setting the threshold to mid-supply (Vcc/2) to detect the zero-crossing or use a frequency-to-voltage converter.

[bernte_one]

thanks a lot

[woodbob123]

I have been considering this my solution so far is using the front end of Carls mag sensors and chip from Speake sensore and then use the arduino to either read the voltage or directly read the digital signal however I have no idea yet how to programme the arduino so far only used arduino as a simple timer.

[bernte_one]

i made some test with hmc5883 sensor it is sensitiv enough an could act as a mag for ferrous searching (conatant reading over serail monitor)

problems is that the arduino can only read one hmc5883 once
because it is not adressable

so it is not possible to build a two sensor mag (differential mag)

solution i had in mind it to take two arduino each with one sensor
one arduino reads and send data to the other arduino
the other arduino read his own sensor and compare his own datas with the datas wich came from the other arduino

the was a thread an arduino forum with the title" read two inputs and compare them"

this can be adapt for this project
the two sensor reading are compared if the difference between the is higher than ähm say reading of for example 5counts lower or higher to the other

the arduino wichih compares the has to give a signal on digital out (piezo)

or led with rising brightness in relation to the compared ratio which came from sensors

just an concept

[bernte_one]

if that concept would work
it is possible to build a differential mag for under 50€
2 arduino mega
2 sensors hmc5883
a carbon fibre pipe for the sensor
and an electronic box
some wires and elctronic crap hat lays around

[sled]

i made some test with hmc5883 sensor it is sensitiv enough an could act as a mag for ferrous searching (conatant reading over serail monitor)

problems is that the arduino can only read one hmc5883 once
because it is not adressable

so it is not possible to build a two sensor mag (differential mag)

No problemo, here are 3 possible solutions:

1. Use an I2C bus switch/multiplexer IC, like the PC9543 (there are many alternatives, I've just picked one). Costs about 1-2 Euros.




2. Just use a quad-bilateral switch IC like the goold old 4016 to multiplex the SDA/SCL lines, alternatively a CMOS device from the 74HCxxx family can also be used. Costs less than 1 euro but might bring some trouble if you go high-speed on the I2C bus due to capacitance issues, but it's definetly worth a try! You could even use a pair of NPN/PNP transistors to switch the SDA/SCL lines.



3. You don't use any external components and just hook the SCL/SDA lines of your second sensor to some free digital IO pins on arduino and bit-bang the I2C in software (software I2C). Costs nothing!

• http://playground.arduino.cc/Main/SoftwareI2CLibrary
• http://blog.arduino.cc/2010/10/01/softi2cmaster-library-lets-you-add-i2c-to-any-arduino-pin/