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Topic: Electromagnetic Wave Sensor (w/ Hall Effect & JFET (Read 2 times) previous topic - next topic


Okay, so I'm a noobie. I've had my arduino duemilanove for like 2 years now and I still dont know how to use it...  :-[


I have 2 transistors, a Hall Effect Sensor (US5881) and a JFET (MPF102). Technically, one will measure H-field strength and the other E-field strength. I want to export the analog output of both these devices to a txt file through the serial, so I can graph the output variations to give me visual on the magnetic wave and electric wave at any given moment.

PURPOSE: I want to figure out how much power exists in the EM wave(s)/radiation in the vicinity of these devices. So that's P = (1/2)*E*H.




Dec 01, 2010, 11:05 pm Last Edit: Dec 01, 2010, 11:06 pm by robtillaart Reason: 1
Used a A1301 Hall Effect sensor in this sketch

Download the US5881 datasheet from
and you will see it's output cannot be used to measure the strength of the magnetic field. This sensor will switch OUT state at two threshold values.

No experience with the MPF102
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)


Okay, so I basically want to use the arduino as a dynamic voltage recording device.

Mr. Crowley, to answer your questions... yes, i need help with all of those. Actually I have a head start with the last question. I have a mac and  using the following syntax in the terminal to write serial data to a txt file:

cat /dev/cu.usbserial-A6008t0M 9600 >> MyTextLog.txt

I've used this successfully, but may need some clarification on what would happen with 2 analog ports exporting data at the same time. What does the serial data look like. Haven't done that yet.

robtillaart, I checked the Melexis data sheet and I don't get it. Are you saying I cannot extrapolate the magnetic field strength from the numerical results? the datasheet clearly states the range of output voltage. can't this voltage reading be used with reference to the hysterisis chart to determine the H-field strength at that voltage?

I'm lost what do you think guys?


I want to figure out how much power exists in the EM wave(s)/radiation in the vicinity of these devices.

I don't think you can do this. The variations in an EM wave will be so fast that all you will get is an average which will be zero.
What frequency of wave were you thinking about?


low frequencies. but now that i think of it, you're right. I should take that into account beforehand. tell me, doesn't the baud rate determine how fast the values are coming in and at what frequency the EM wave is that will be probed?

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