Do Hall Effect sensors output varying voltages based on magnet's strength?

Other Hardware Sensors
1

Hi all! I've just started my first arduino project and I'm stumped as to how to complete my next step.

For reference, I'm trying to build a board which takes small blocks as inputs. There will be four types of blocks (up, down, left, right) all with the same shape and 12 slots on my board. I want to be able to put any block in any of the slots and be able to detect which block is in which slot. Essentially, I want to know the order of the random blocks that are placed. I'm trying to figure out a cost-effective and a simple yet reliable way for my board to distinguish the blocks.

From what I can tell from googling around, it seems as if hall effect sensors can output varying voltages depending on the magnet's strength. If I were to hook up a hall sensor, and I have 4 different magnets of varying strengths, will it be able to reliably distinguish the magnets based on the voltage output (assuming the programming to do so is there)? If it's possible, can the magnets be roughly around the strength of that on a typical magnetic chess piece? Or would that range of magnet strength be too small to reliably detect a difference in magnetic field strength? Using a larger range of magnet strength would probably work better, but I want to keep all of the magnets to around the range of a magnetic chess piece, so the differences in strength would have to be quite small.

My first idea was rfid, but it's looking like it'd be overkill and unnecessarily too complicated for my purposes. The second was color detection, but it doesn't seem like it'd be reliable and/or elegant.

Another solution I have is to bridge intersecting wires with varying resistance on the blocks. For example, each type of block will have a different resistance embedded into it so that the board can distinguish the blocks by the varying output of the bridged wires. A similar concept to hall effect sensors, but without the use of magnets and sensors. Determining the position of the block should be simple enough using the intersecting wires like a grid. I can't seem to find any information as to whether it'd even be possible to bridge wires externally in that way though.

Any help or suggestions would be greatly appreciated!

Thanks!

2

It all depends on which hall effect device you are using. Some do, some don't.

Generally 'switching' hall effect devices won't, but 'sensing' ones likely would depending on the circuit.

3

Yes, depends on the Hall Effect Sensor type but just for example one like this:

Look to names like Honeywell and Allegro for plenty of hall effect flavors. You could play around with a proof of concept but I can't see why it wouldn't work.

The automotive industry also used a VATS key system where a resistor is embedded in the key. I see your resistor in block scenario as viable also.

http://www.vatskey.com/help.php

I also would not be too quick to rule out RFID and while it may be overkill it works and is not all that expensive anymore.

All you really need is a way to encode the block and decode where any block is placed. Among those mentioned if practical I like the resistive method.

Ron

4

Ron_Blain:
Yes, depends on the Hall Effect Sensor type but just for example one like this:

https://www.alliedelec.com/m/d/cd01bc793b6489eec67e2ac2cb0089ca.pdf

Look to names like Honeywell and Allegro for plenty of hall effect flavors. You could play around with a proof of concept but I can't see why it wouldn't work.

The automotive industry also used a VATS key system where a resistor is embedded in the key. I see your resistor in block scenario as viable also.

How a GM vats system works and how to find or measure your vats code

I also would not be too quick to rule out RFID and while it may be overkill it works and is not all that expensive anymore.

All you really need is a way to encode the block and decode where any block is placed. Among those mentioned if practical I like the resistive method.

Ron

Awesome! After looking into hall effects and their datasheets, I'm currently leaning towards hall effects. Thank you for sharing the VATS key system. That was exactly the example I was looking for, but couldn't find myself.

The purpose of my project is to build a "coding" toy for my young nephew, so a small metal prong might not be the best idea. Plus the extra steps required to make the resistor prong. However, it does seem to potentially be the most reliable as its not relying on any sensors. Maybe a metal plate on plate could work? Or would having good contact be potentially an issue?

I've been reading through the forums of all the folks that have been discussing using rfid, as opposed to the typical reed switch setup, so that they can track individual pieces on a chess board. An 8x8 chess board grid is much bigger than what I'm planning, but the complexity of what needs to be done (like tuning the antennas so that it doesn't pick up adjacent signals) to achieve it goes a bit over my head atm.

I'm new to reading datasheets, but according to the honeywell datasheet that you linked, my understanding is that this particular hall effect will read between -640 to 640 gauss magnets and output a proportionate voltage typically in increments of 3.125 mV/gauss. And any magnet beyond that range will just max out the output thereby not being useful for my purposes. Is this correct?

A typical refrigerator magnet is said to be around 100 gauss, so I'm thinking that using a 100, 150, 200, 250 gauss, for example, should work. Or maybe I can just stack the same magnets to achieve this. Magnets seem to loose their strength fairly quickly with even very short distances, so I'll probably have to play around with the strengths.

I'm also thinking that a bipolar sensor might be better than unipolar as I could potentially just use two types of magnets (or two layers) and reversing the polarity to make 4.

As for the programming, I'm thinking of pre-setting an acceptable voltage range for each directional block to distinguish the input and account for slight variances. But, I'll probably have to actually test the readings to figure out what the best solution might be.

I feel like I'm just thinking out loud, but as I'm new to all of this, I wanted to see if my though process going in the right direction.

Thank you!

5

Magnetic flux density drops precipitously with distance from the magnet, i.e. its very geometry dependent
so trying to guess the range you need is rather hit-and-miss, better to measure it in the actual configuration
you are interested in.

6

MarkT:
Magnetic flux density drops precipitously with distance from the magnet, i.e. its very geometry dependent
so trying to guess the range you need is rather hit-and-miss, better to measure it in the actual configuration
you are interested in.

Yeah, I'm realizing that the flux density drops significantly even at just 5mm distance, which might be a problem since I want to work with magnets that are already fairly weak. But it might also be good in that now I can use magnets that are in the 1000s range. But I'll have to test that out to make sure.

So basically, I should pre-set a distance that I'm liking going to use, find a magnet that will give me 1v, then find another magnet that will give me 1.5v and so on? (the voltages being arbitrary numbers)

7

My advice would be get a sensor or two (hall effect) and a few magnets and play around a little with distance and change. Both sensors and magnets are inexpensive. That should give you an idea of how practical things are. Yes, flux density is not a linear function but still worth a shot.

Ron