Vyper2 Compass Issues

So, if I mount an SK7 compass on the top of my console, above my Vyper2, (or on the back behind the SPG for that matter) will the magnetics of the Vyper2 compass conflict with the magnetics of the SK7? (Assuming I never activate the compass on the Vyper2) Anyone try this?

Some helpful guys beat this issue to death in a post I made. Sharing....

Quote:
Originally Posted by ianw2
As I have mentioned many times before, there is no such thing as a "digital" compass. It is a digital readout for a miniature compass. It still uses a magnetic needle to align itself to the earth's magnetic field as every compass eve built for the past 3 thousand years.

A digital compass is actually *quite* distinct from your classic magnetic compass. In your classic magnetic compass, you have a small movable magnet which aligns itself with the local magnetic field. A digital compass, on the other hand, takes advantage of the fact that charged particles moving through a magnetic field are deflected in a direction normal to both the direction of the magnetic field and the direction of motion of the charged particles. (Actually, this is the same phenomenon that classic cathode ray tube televisions made such amazing use of.)

In the case of a Hall-effect sensor, which is a semiconductor device (like a diode or transistor), the current flowing through the sensor (which is *minuscule*) from one end to the other in the presence of a magnetic field (such as *earth's*) yields an even more minuscule potential difference from one side to the other. This tiny potential difference is what is measured and processed to give a heading.

The digital compass in, for example, a Suunto Vyper2 is a "one-axis" electronic compass. It is sufficient to tell heading, but only when held very close to level. The first consumer GPS receivers we geocachers used were similar, and the results were just slightly better than pathetic. More recent GPS receivers use multiple Hall-effect sensors in order to be able to compute heading in three dimensions, which allows them to tell you your direction regardless of the angle at which you're holding the GPS receiver. (Their algorithms generally project the heading vector onto the plane of the local surface of the earth, although it would be quite cool to have a dive computer that gave you a true three-dimensional heading.)
Quote:
Originally Posted by ianw2
The two magnetized needles, one from the digital compaas and one from the "analogue" compass, will be attracted to each other rather than swing in the earth's magentic field.

You can see what happens when you put two normal compasses together. The same thing will likely happen with the Viper2 in the same console as the compass. The result: you're really going to get lost!

The magnetic field of the classical compass can be significant. It has to be strong enough to quickly move a needle -- more often, an entire compass card (as the disc with markings is called). Having two such compasses near each other can *certainly* pose a problem. On the other hand, there is no such issue with the *minuscule* magnetic field caused by the tiny currents in the computer. (If they had an electromagnet strong enough to affect an SK-7, the battery life would be on the order of *minutes*. )

It is *utterly* irrelevant to an SK-7 that there is a digital compass nearby. On the other hand, with the substantial magnetic field of an SK-7, placing it right next to a Vyper2 will almost certainly cause the Vyper2's digital compass to misread. (If you want me to make a video and post it on YouTube, I can certainly do that. I just tried it out, just to make sure there wasn't some confounding factor I may have missed, and the effect is indeed dramatic. Facing north, both compasses read north. When I bring them together, the SK-7 has not moved at all, but the Vyper2 has practically flipped almost to due south thanks to the magnetic field from the SK-7.)


Quote:
Originally Posted by ianw2
With any luck, this generation of computers will be the last one we see with this useless, and potentially dangerous, device embedded.

Hopefully, I've done at least a little to help clear up your misunderstandings. Electronic compasses are certainly not useless (although I prefer the better visual feedback and usability of my SK-7). Calling them "potentially dangerous" is untenable (especially when we strap virtual bombs to our backs and tempt fate every dive ). Of course, if you have an SK-7 mounted adjacent to a computer with a digital compass, the digital compass is not usable, so I will concede that minor sub-point. (The regular old magnetic compass is completely unaffected, of course.)

Frankly, I don't much care for mine, but I have jarred my SK-7 on a dive before. It jumped the fulcrum and the card jammed. Had I needed it, the jam-proof electronic compass on my Vyper2 could have come in quite useful. (I consider it a worthwhile backup.)

I hate to be duplicative, but the formatting is all off in the copy-and-paste above, so I'll quote myself from the earlier thread. :biggrin:

ClayJar:

(...posted indented below to preserve formatting...)

Click to expand...

*Anyway*... The long and short of it is that the SK-7 will not be affected at all by the presence of the computer, but the computer's electronic compass will almost certainly be affected by the magnetic field of the SK-7 compass. I have neither my computer nor my SK-7 mounted in a console, so I can't give quantitative numbers, but I am quite confident the computer's electronic compass ought not be relied upon in such a situation.

Of course, if you have the SK-7, why use the battery-eating electronic compass anyway? Assuming you never bother with it, it is utterly irrelevant (like it's not even there). If you ever break the SK-7, a few turns of a screwdriver can temporarily remove the SK-7 from your console. (If it's back mount, keep the non-compass back in your save-a-dive kit; if it's end-mount, you need nothing but the screwdriver... and more O-rings, of course -- we always need more O-rings. )

Thank you, tkdgodess, for pointing me to that thread. I actually came across it when I first made a search on this subject, but I only went through the first page.

And thank you again, ClayJar. This is at least the second time you've helped me out with a computer question. I, too, am not fond of the compass in the Vyper2. (I am also a Geocacher and I have been spoiled by my Garmin eTrex, I just wish I could use it underwater!) I think you've answered my question, but your explanation leads me to another one. For the sake of argument, lets say the current flowing through the sensor of the Vyper2 compass is indeed enough to effect the SK7, is that current actually flowing when the compass is NOT activated or is the entire compass circuit turned off (and therefore not emitting a magnetic field)? I think you've actually answered that one too, but I'd just like to clarify that.

Thanks again!!

While I don't have a circuit diagram of the entire internals of the computer in front of me, I'll say that I see no reason the electronic compass circuitry would be powered more than just when in actual use. It would be a drain on battery life for no reason at all. (The sensor is just another bit of electronics, like the LEDs on your computer keyboard. Since it can be energized and turned off at will, it would be terribly poor design to "leave the light on" all the time, especially in something powered by a large watch battery.)

Of course, even with the sake of argument observed, I can't help but note that is isn't enough current to create any notable magnetic field in any case. :biggrin:

Thanks, yet again!