Conducive Magnetic Connectors

[Scott Silvi]

Hey all -

I'll preface this with I'm a software engineer by trade, and have been getting in to the maker / tinkerer / open hardware space the last few months.

Here's my scenario. I have a stationary object w/ a micro controller on it. I have a remote sensor in a mechanical device that is mobile. Occasionally the device will be connected to the main terminal via a hose. When this happens, I need to power the remote sensor & receive data back. There's currently a wire wrapped around this hose that provides grounding from terminal to device. I can add a secondary wire around the hose, but need a way to complete the circuit on both ends of the hose from my micro controller to my sensor. I could do this with any number of male / female connectors, but my ideal would be something that doesn't require user intervention to connect.

My remote sensor has a 2 (analog) or 3 (digital) wire output. I can either run ground / signal / power in my secondary wire directly to my sensor, or I could drop another micro controller in the remote device, connect my sensor, and just send voltage back up the wire (that makes sense in my head, but you might be calling me all kinds of idiot for what I just wrote!).

Without a lot of experience in conductive connectors, the best I've come up with is this conductive magnetic connector:

https://www.rapidonline.com/tools-equipment/magnetic-electrical-connectors-5-pairs-34-0915

The description of that product says its good for prototyping, etc, which may not be robust enough, and it also looks like it's only one wire, so I'm not sure about signal / ground / power. I've also been looking in to ring magnets, like this guy:

https://www.kjmagnetics.com/proddetail.asp?prod=RA22CS-S

So two questions, really:

1) Am I overlooking something that would be an easier solution than the path I've gone down, and
2) If i go with this magnetic connector, how do I supply signal / power / ground? Can I simply run power down the hose into a micro controller (like an Arduino for prototype), and use that board to provide signal / power / ground to my sensor? How then do I send voltage back up the wire? Do I need a second magnetic connector? Theoretically I could drop in like a bluetooth module, but I'd like to avoid the additional expense & hassle

[Edit to add]
I'm more than happy to do a ton of research on this, but I'm kind of struggling with knowing what to search for, so even a prod in the right direction would be tremendously helpful
[/Edit]

 

[k7elp60]

If I understand correctly, you need two wires for the power + and -. And one wire for signal. It is possible to use the power wire for both signals both ways and the power also. This is done by isolating the power from the signal at both ends. There are connectors that slip together and make good contact, which would be an option.

 

[JimB]

JimBs comments in RED

Here's my scenario. I have a stationary object w/ a micro controller on it. I have a remote sensor in a mechanical device that is mobile.
How big are these "devices"?

Occasionally the device will be connected to the main terminal via a hose.
This hose carries fluids? Fuel? Water?
When this happens, I need to power the remote sensor & receive data back.
Is there any source of electrical power in the mobile device?

There's currently a wire wrapped around this hose that provides grounding from terminal to device.
This suggests to me that the hose is carrying something flamable.

I can add a secondary wire around the hose, but need a way to complete the circuit on both ends of the hose from my micro controller to my sensor.
Pin to pin connectors seem a good idea to me.

I could do this with any number of male / female connectors, but my ideal would be something that doesn't require user intervention to connect.
How hard is it to attach the hose and an electrical connector? Just two connections.

These magnetic connectors sound like a disaster waiting to happen.
If you want a one operation connection of hose and cable, could you make some kind of a stab plate which holds both the hose fitting and the electrical connector, and just stab it into the corresponding plate on the moving thingy?

Why can't you just tell:
What is the moving thing?
What is the hose for?
What does the sensor measure?
If there is power on the moving thing, could the sensor data be sent by radio?
So many questions!

JimB

 

[Scott Silvi]

Thanks guys.

Sorry Jim - I was trying not to inundate you guys with too many / unnecessary details, so I was trying to isolate the components of this system that were relevant. Obviously I failed.

First off, I don't think I'll need an additional ground. The hose itself already has ground running through the elbow (the mobile / remote device - more on that below), so I should be able to ground straight to that.

I'm building a what amounts to a flow meter /overflow system for a small fleet of flatbed fuel trucks. On the truck itself, I'm mount a device with a small circuit board w/ a few signal wires running to various valves / components. One of these wires (along with power, which will come from the truck) runs to the api head where we offload the fuel (which can be one of many different types of flammable / hazardous liquids). A hose connects to that API head, then out to a simple mechanical locking device (usually in the form of an L shaped elbow). The elbow then connects to the receiving fuel tank, usually (but not always) underground.

As far as the sensor - if your receiving tank only needs 1000 gallons to be full, and the truck has 1001+, you end up overfilling the tank. If this is at a gas station, for example, you first shut the valve on the truck, then literally have to sit there and wait for enough vehicles to come and purchase enough fuel to empty out the hose, elbow, and however much lead is in the receiving pipe before you can close the valve (anywhere from 30-50 gallons, usually). In remote areas, this can literally be an entire day of waiting. We're working on a system that will mitigate this by electronically closing the valve before the overflow can occur.

To answer your questions, the device on the truck can be whatever size we need (within reason - the toolbox I plan on mounting this in is about 3x3x1.5). We use 4 inch piping, so the elbow is a L shaped 4 inch pipe that stands about 2 feet tall. The sensor will be mounted inside of the elbow. There is currently a ground wire wound around the hose, which grounds the truck through the elbow, which itself has no power.

Pin to Pin is my absolute last resort. I'm basically looking for a fool proof connector, one that minimizes or removes driver involvement, as they are notoriously hard on our components, and I've been asked to do everything I can to preclude an extra step being added to the process. I've also considered something like the magsafe / magcode, which is pins embedded in a magnet, where the magnet itself provides no conductive material, simply a breakaway connector.

The problem with using short-range communication (I've considered bluetooth), is a tank might have a couple of compartments, and the truck carries a couple of elbows. If I have a sensor in an elbow that says "woah, stop", I won't know *which* compartment I'm hooked up to; ergo, I don't know which valve to close. I could absolutely shut them all down, but I have a requirement that says not to do this. Because the tank compartments & elbows are universally used across all of our liquid materials, I have no way of knowing which device is connected to which compartment.

Hope that helps.

Scott

 

[alec_t]

No-one's so far mentioned safety requirements . If you're handling hazardous/inflammable liquids aren't there stringent rules as to what types of connectors/radio-links/grounding-arrangements can legally be used?

 

[ClydeCrashKop]

I've also considered something like the magsafe / magcode, which is pins embedded in a magnet, where the magnet itself provides no conductive material, simply a breakaway connector.

I vote for that. Here are a couple links.
https://www.rosenberger.de/en/products/medical/magnetic.php
https://www.rosenberger.de/en/products/automotive/magcode.php
https://www.rosenberger.de/en/products/automotive/magcode.php

 

[Scott Silvi]

No-one's so far mentioned safety requirements . If you're handling hazardous/inflammable liquids aren't there stringent rules as to what types of connectors/radio-links/grounding-arrangements can legally be used?

There are requirements, yes, but they're not spec'd to "if you're going to run a device in the elbow, you have to do X". We'll get certified well in advance of this going on any truck.

Thanks Clyde - that's the magcode I was looking at. Glad I was on the right track.

Last night I started looking at RFID tags that would be permanently placed on both ends of the hoses. I could have a reader on the truck, and a reader on the elbow, that would provide the electronic handshake I need to confirm which elbows are hooked to which compartments. So far, that seems promising. I'd be able to use something like bluetooth in this case. Again, higher cost, but perhaps better solution... I'm not exposing connectors to corrosion via ice, snow, slush, sand, salt, etc.

 

[ClydeCrashKop]

I haven't worked with Bluetooth. Microcontrollers use I2C and other communication protocols where devices have their own address number so they know if they are being talked to or who is talking. (Like phone numbers) You could have multiple displays / alarms, each with its own sender, or one display / alarm that could tell you which sender was activated.

Bluetooth would also eliminate sparks and user intervention.