Hall Effect Sensor selection help

As is the case there are a thousand to choose from and not enough experience to choose one. lol

I have a stepper moving a small table in and out and thought I would add some position sensors to control my repeatability for different movements and just need something simple.

I would like some type of finished product with covered wires to connect to my UNO and screw or glue into my rails. I was looking at this (http://www.littelfuse.com/products/magnetic-sensors-and-reed-switches/hall-effect-sensors/55100.aspx) and was confused about what option I should be looking forget don’t know the questions I should be asking myself about it.

All my digital pins are used up so I would have to to send the input to the analog side of the board.

Reading the data sheet it wants to know output type (current,voltage,analog voltage) for each sensorso I’m guessing I would get analog voltage?

Any help with the selection process is appreciated.
Thanks

I have a stepper moving a small table in and out and thought I would add some position sensors to control my repeatability for different movements and just need something simple.

All my digital pins are used up so I would have to to send the input to the analog side of the board.

The analog pins can be used as regular digital pins, and in my opinion you are better off using digital sensors for the positional limits.

Hall effect sensors are NEAT! I have several to investigate in my "to do" pile.

You need to be aware that they are MUCH more than silicon reed switches.

For some, the output goes high when a magnet is around, low otherwise. (I THINK there are some like this!)

Others are "fancier"... only going high when the "north" pole of a magnet is near. Or something like that. As I say... I'm no expert!

Some, I think, latch: Go high when they see north, and stay high until they see a south. I think.

=== Well done spotting the hints of complexities in the data sheets. Post a reply to this when you pin them down, know more than my sad "one eyed king" contribution!

cattledog: The analog pins can be used as regular digital pins, and in my opinion you are better off using digital sensors for the positional limits.

I had read that and was looking into it. The sensor data sheet shows 2 types, one outputs voltage and the other outputs current and wonder what the different uses would be for each? Would I be wrong to choose either of them?

tkbyd: Hall effect sensors are NEAT! I have several to investigate in my "to do" pile.

You need to be aware that they are MUCH more than silicon reed switches.

For some, the output goes high when a magnet is around, low otherwise. (I THINK there are some like this!)

Others are "fancier"... only going high when the "north" pole of a magnet is near. Or something like that. As I say... I'm no expert!

Some, I think, latch: Go high when they see north, and stay high until they see a south. I think.

=== Well done spotting the hints of complexities in the data sheets. Post a reply to this when you pin them down, know more than my sad "one eyed king" contribution!

I will do so.

The sensor data sheet shows 2 types, one outputs voltage and the other outputs current and wonder what the different uses would be for each?
Would I be wrong to choose either of them?

For your application and use with the Arduino, you want the three wire types, which they call a “voltage output”.

This is also known as an “open collector” output, and will require an external pull up resistor to a voltage source in order to create a signal which will be at the pull up level (5V) when the magnet is not present, and ground when the magnet is in front of the sensor. The pull up should be sized to keep the current through the sensor below the spec of 20ma. 1K would not be a bad choice.

cattledog: For your application and use with the Arduino, you want the three wire types, which they call a "voltage output".

This is also known as an "open collector" output, and will require an external pull up resistor to a voltage source in order to create a signal which will be at the pull up level (5V) when the magnet is not present, and ground when the magnet is in front of the sensor. The pull up should be sized to keep the current through the sensor below the spec of 20ma. 1K would not be a bad choice.

Thanks cattledog, I did know about the resistor from learning about the sensor and most everything I have looked at has 3 wires, seemed way easier to wire up and easy is best for me.

I wonder if the sensor I have in my first post will allow me to have the slide table start in different positions. I'm running 2 different code blocks at separate times depending on what I'm doing and didn't know if I could code it to say start at the sensor minus 1 inch and then do the code block or do I need something along the lines of a rotary type sensor to measure the steps somehow?

I wonder if the sensor I have in my first post will allow me to have the slide table start in different positions. I'm running 2 different code blocks at separate times depending on what I'm doing and didn't know if I could code it to say start at the sensor minus 1 inch and then do the code block or do I need something along the lines of a rotary type sensor to measure the steps somehow?

With the stepper motor, you can know where you are by counting steps, but you need to have a known positional starting point. When you start up, you will need to find one end sensor and then begin. You may need to just come back off of this home position if you want to take up mechanical backlash of the directional reversal.

The mechanics of your system and the positional accuracy requirements will determine if you need additional encoders, possibly linear ones, for table position feedback or if the stepper counts from a known position will be adequate.

cattledog: With the stepper motor, you can know where you are by counting steps, but you need to have a known positional starting point. When you start up, you will need to find one end sensor and then begin. You may need to just come back off of this home position if you want to take up mechanical backlash of the directional reversal.

The mechanics of your system and the positional accuracy requirements will determine if you need additional encoders, possibly linear ones, for table position feedback or if the stepper counts from a known position will be adequate.

That definitely helps with the selection process.

I'm back to working on the sensor and went to the store and picked up a cheap Allegro A3144 sensor to play with. It really is simple for wiring and I used a sketch for turning an LED on and off by moving a magnet around it to move it high and low. The next thought I have is how to tell the arduino to find the sensor, the code I ran today doesn't look for the sensor but actuates the pin when a magnet goes by but have yet to stumble onto anything that has the arduino look for the sensor(home position in my sketch to be).

If anyone has thoughts of where to look or more importantly the right question to search I would appreciate any bread crumb.

If anyone has thoughts of where to look or more importantly the right question to search I would appreciate any bread crumb.

Use the forum search box at the top right of the forum website, and type in "find home position stepper motor".

It's quite simple. Mount the hall sensor in a fixed home position. Fix the magnet to the table so it will be in front of the sensor at home position. Read the sensor with digitalRead(). Is the magnet in front of the sensor? If yes, you're home, if no, move one step. Repeat as necessary.

Thanks cattledog, just after I posted this someone started a thread about it and it really was pretty simple, I was most of the way there thinking abut it but having just started I always wonder if I'm thinking it through correctly.