[Moved]Electronic compass

Catspaw, some information about your project would be useful, particularly how it relates to HDMI line protection.

Brian.

HA! Thank you for replying. I was not really expecting a reply, especially this soon. It is going to be an anchor warning device. I want to create an output signal that if the device changes direction by 8 degrees for 8 seconds, an output signal is activated. The little research I've been doing points me to a magnetometer (spelling?) or electronic compass). I think the one I want is HMC5883L.
Can we text back and forth about this? [phone number removed]. I am Robert - or Rob.

Putting your email address or phone number in a message is inviting it to be harvested by spammers! Besides, some of us are on different continents and phone calls are expensive! Please correspond through the forum so we can share ideas and suggestions. I have also started a new thread and moved these messages to it as a new topic is being created.

The optimal solution depends on the circumstances. You can do it with a magnetometer but only if the surrounding magnetic field is stable and you may need to average the readings to eliminate the small random variations a magnetometer might produce. Can you tell us what environment this anchor is in and whether it is possible to mount other things near to it. If you are trying to sense rotation but on a stationary spot, there are probably easier and cheaper options. How accurate does the 8 degree shift and timing have to be and do you feel comfortable to use a microcontroller?

Brian.

Wow. Got lost. There is some wriggle room in the accuracy. Actually, I'd like a component that I can dial in these numbers to tune it to a good operating range. It will go on a boat that anchor's "out in the stream". Its a long story how this came up, and yes, I know Garman and many others make things like this based on GPS, but this is an opportunity for me to get into electronics and build something useful, and yes, show off a little.

I'm back. I am calling this my "Compass Project". Voltage: Overall, there will be a number relays and relay contactors involved. I would like to think all this needs to operate at the same voltage. I keep seeing 3.3vdc come up. The final product output I will amplify to 12 vdc for a horn and some LED lights. Should I select another operating voltage?

Magnetometers do not work well near ferrous materials like anchors.
A gyro is a sensor that measures degrees per second.
Sparkfun used to sell them https://www.sparkfun.com/products/retired/11028

But these fragile parts do not like water.

What we need to know is how you intend it to work. An anchor is usually attached to a boat so you can detect movement by noting the strain on the anchor or the position of the boat itself. As Tony points out and I eluded to in post #3 when I mentioned a stable magnetic environment, a magnetometer measures magnetic field so you can't rely on it detecting Earth's field in the presence of other magnetic materials.

Are you trying to find the direction a boat is pointing? If so a gyro or even GPS might work. I live on an estuary and the river outside my house is tidal, all the moored boats turn around 180 degrees each time the tide turns, is that what you want to detect?

As for voltages, most horns and alarms work on 12V and most electronic devices these days work on 5V or 3.3V. It isn't a problem, you just have to regulate the higher voltage down to the lower one and use some simple circuitry to make the lower voltage operate devices using the higher one. Regulators and driver devices are plentiful and mass produced so their price is usually very low. Normally, the 'thinking' part of a design is a microcontroller working on 3.3V and a transistor driver is used to interface it to higher power loads.

Incidentally, have you noticed the physical size of the HMC5883L? you might think twice about how to solder it before buying one!

Brian.

Electronic compass projects used to be more common, based on hall-effect sensors. The type I'm aware of put out a neutral signal unless they sense a magnetic field oriented in a certain direction. Even the earth's magnetic field (weak as it is), with assist of amplification. You held the unit as you turned toward different directions, until it measured highest intensity which was North.

I saw a more complex project which had two hall sensors on opposite ends of a circuit board. One to detect a North Pole, the other to detect a South Pole. Thus it's least likely to be disoriented by false readings.

I've stood a small disc magnet on edge on a smooth tabletop, and it turns by itself to face north/south. Or floated it on water in a little raft. No iron or steel can be nearby.

I don't know how similar a magnetometer is to a hall sensor.