Gaussmeter - hall-effect sensors

I'm

through

16F876A

my

supply

9.999 99.99?

I don't believe you have enough bits in the PIC ADC's to do what you want. These ADC's are 10 bits and if you use all 10 bits you have one part in 1024 as the maximum resolution. You are asking for one part in 10,000 which at minimum would take 14 bits. In order to provide head room and less fooling around with precise analog range, gain and offset, I'd go for a 16 bit ADC. You can still use a PIC for linearization and display taking two bytes at a time and processing as a 16 or 14 bit word. Bob

Good point. :-) They also do some 12-bit ones, but they may be relatively pricey.

Okay, I'll look into that a bit more.

Cheers,

--
Melodolic Spielberg

Take a look at the Analog Devices AD7705/7706. It's pretty easy to use and has some nice amplifiers built in.

Mike

------------------------------------------------------------------------ The odds of a single modest length protein randomly forming is approx

1 in 10^260. By comparison the number atoms in the known universe has been estimated at 10^80 atoms. Figues are from the writings of Nobel Prize winner Francis Crick in 1981.

Been looking at the 7705 datasheet, and I suspect that this is a bit more than I can chew just now - all that inter-chip serial stuff. Methinks I'll go for finishing the basic gaussmeter I've got, try it out, and come back to the increased sensitivity later. Thanks for the pointer, though - A/D is something I want to learn more about.

I wonder how they work that out.

--
Melodolic Spielberg

I used to make cheap little Gauss meters and had pretty good results with an analog front end driving a 3 1/2 digit DPM. Only 2000 count tho. They measured -1999 to +1999 Gauss with a 1 Gauss resolution. After warmup they would drift about +-1 Gauss, the best I could tell. I later switched to using a PIC and LCD using an LTC1298 dual 12bit serial A/D because it was cheaper and easier to build. The serial stuff isn't that hard after you've done it once or twice. I'm not sure I would attempt a full 4 digit accuracy, Not sure, but I don't believe standard Hall sensors are that stable.

Here's a brief description of how it was calculated with a reference to the original work.

This is an easy exercise in combinatorials. Suppose the chain is about two hundred amino acids long; this is , if anything, rather less than the average length of proteins of all types. Since we have just twenty possibilities at each place, the number of possibilities is twenty multiplied by itself some two hundred times. This is conveniently written 20^200, that is a one followed by 260 zeros!

This number is quite beyond our everyday comprehension. For comparison, consider the number of fundamental particles (atoms, speaking loosely) in the entire visible universe, not just in our own galaxy with its 10^11 stars, but in all the billions of galaxies, out to the limits of observable space. This number, which is estimated to be 10^80, is quite paltry by comparison to 10^260. Moreover, we have only considered a polypeptide chain of a rather modest length. Had we considered longer ones as well, the figure would have been even more immense.(Life Itself, its origin and nature, Francis Crick, 1981, pp

51-52)

Mike

------------------------------------------------------------------------ The odds of a single modest length protein randomly forming is approx

1 in 10^260. By comparison the number atoms in the known universe has been estimated at 10^80 atoms. Figues are from the writings of Nobel Prize winner Francis Crick in 1981.