# help with simple question needed

Discussion in 'Electronic Basics' started by Beowulf, Feb 2, 2004.

1. ### BeowulfGuest

I just built the gaussmeter from plans at
I am just a newbie, and know little about electronics.
Two questions for anybody that can help me:
(1) Is there any way to increase the sensitivity of the gaussmeter
perhaps by putting two of them in series or something?
(2) Is there any way to build my own gizmo to input this into my
laptop computer serial port? I found a gaussmeter probe that hooks
into a laptop serial port, with basic software to write comma separated
value data values, and even this costs \$500. I would like to build my
own such setup if possible to collect magnetic field info in real time.
~Randall

2. ### CFoley1064Guest

(1) Is there any way to increase the sensitivity of the gaussmeter
Hi, Randall. Two questions, two answers:

1) I'm assuming you are using the Radio Shack sensor. That one (Allegro 3515)
has a sensitivity of 5mV/G. You might want to special order the 3516 mentioned
in the app note. It has a sensitivity of 2.5mV/G. However, I'm not sure
that's your problem. You've got a sensor that has a "zero" output of around
+2.500V, and you want to detect small differences from that "zero". The way to
do this is to use a voltage offset. Here's the easiest way to do this (read in

SW1 ____
_/ | |
.-o/ o-.------|7805|----.-------.-------------.
| | |____| | | .---o---.
| | + | | + | | | +
+| ### | ### | | HE3505o-------o
--- --- | --- | P1 | |
- C1 |10uF | C2 |10uF .-.10K '---o---'
9V | | | | | |<---. | DVM
| | | | | | | |
| | | | '-' | |
| | | | | '-------------------o
| | | | | | -
| | | | | |
'-------o--------o-------o-------o-------------'

By using a 10K pot (preferrably 10-turn if you can scrounge one), you can set
the pot wiper so there's no differential voltage between the pot wiper and the
sensor output when there's zero gauss. That will allow you to put your DVM on
the 200mV range instead of the 20V range, which is probably the main reason
you're dissatisfied with what you're getting from the sensor. 5mV/G is really
pretty sensitive for one of these things.

2) If you're interested in a cheapie kit that will do what you want, you might
want to look at the GP-3 PC I/O Board Kit from al-williams.com. It's based on
a PIC, and gives you 8 general purpose I/O lines, 5 ea. 10-bit A-D conerter
pins (5mV/bit), and a lot of other good stuff. It's based on a PIC, and the
kit is only \$40.00. You won't have any trouble reading the above circuit with
the GP-3, and getting it in to your PC from the serial port. They even give
you sample programs and source code in the languages of your choice, as well as
the serial protocol if you want to roll your own.

http://www.al-williams.com/gp3.htm

Good luck
Chris

3. ### Jacobe HazzardGuest

One way to simplify things and still save a bit of cash is to use a DMM with
an IR or RS232 PC link. For well under \$500 you can get datalogging and
probably some features that would simplify your circuit and solve your
sensitivity problem.

4. ### BeowulfGuest

I am pretty naive regarding all this stuff-- basically the gaussmeter I
built works, but I only see changes in the output voltage when a magnet
comes within maybe 4 or at most 6 inches of the Hall Effect component. I
would like to detect electromagnet signals several feet away -- is that
even possible with a home-built gaussmeter?

BTW thank you for such a nice reply, I am still looking at it as like I
said I only know basic electronics, though I did build and solder some
simple electronics projects as a teenager.

5. ### BeowulfGuest

..
The only pot I know is the kind I used to smoke (smile) or the kind I
cooked my spaghetti in tonight! Can anybody translate? Pot? Pot wiper?
DVM -- can I buy a vowel???

So you are saying that for about \$40 I can built something to be able to
input voltage signals e.g. from a gaussmeter, including some primitive
software? That would be outstanding-- \$500 for a commercial product just
is outside my budget for what I have in mind. Electronics always seem
overpriced to me as there always seems to be next to no components
inside the box.

6. ### DougGuest

DVM =Digital Volt Meter
Pot = potentiometer i.e a varible resistor with a connection at each end
plus a third contact that can be moved. usually by turnning a knob. A
volume control is an example.

7. ### JeffMGuest

Pot? Pot wiper? DVM -- can I buy a vowel???
Well, maybe someone can--but if you don't understand the shorthand for
variable resistor and digital voltmeter, it might not be you.

8. ### CFoley1064Guest

From: Beowulf
Probably not -- the effect decreases proportionally to the square of the
distance, and that's quite a distance, unless you've got quite a magnet.

Possibly you could tell us a little more about what you're trying to do? There
are other ways of sensing from a distance. Retroreflective opto comes to mind
-- in an industrial environment, that's usually a first choice.

Good luck
Chris

9. ### CFoley1064Guest

From: Beowulf
knowledge about electronics than you have -- that's OK. A pot is a
potentiometer, which is the variable resistor you use, for example, as a volume
control. As you turn the dial, you increase or decrease the resistance. If
you're setting this thing up on a perfboard or solderless breadboard, you
should use something like the Radio Shack Cat # 271-343, which is a 15-turn, 10
K ohm potentiometer which is available for \$2.49 USD.
Again, revising the answer to your level of knowledge and experience, you
probably should go with the advice of another respondent, and use a DVM
(digital voltmeter) for input. Many meters have built-in RS-232 output, and
also have software included which will allow you to just plug it in and chug
away (plug&chug). A good choice for a newbie would be the Radio Shack Cat. #
22-812, on sale at all stores for \$59.99 USD. Included with the meter is some
elementary software which will allow you to get unattended data collection.

That will do it, in and of itself, for a total newbie. If you have trouble
hooking things up or getting it going, you should be able to ask anyone with
any technical background -- it's pretty simple. If you have questions about
the data collection software, the manual is on the disk.

Good luck.
Chris

10. ### BeowulfGuest

Hey thank you so much. I ordered the GP-3 PC I/O Board Kit from
http://www.al-williams.com/gp3.htm for learning to collect data into a
serial port, and I am going to get the Radio Shack parts, pot, and DVM
with software that you suggest. Lots of toys to play with! I will
probably be back here in the near future with a few questions. I have
soldered a pot in my distant past (I recall building an electronic
mosquito repellent, etc.), soldered resistors, even taught basic physics
of ohms, etc. But I really have little practical experience building
this stuff. I have even done a fair amount of computer programming (C++,
java, BASIC) in my past, so hopefully I can play with custom code to
control the analog to digital data acquisition.

11. ### CFoley1064Guest

From: Beowulf
Start out with the Radio Shack DMM and the schematic with the 10K pot -- that's
the easiest, and will probably get you close to the best results you can get on
a hobbyist level.

Good luck.
Chris