Hal-effect velocimeter probe and teensy ++ 2.0

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Pixe

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Hello,

I have a teensy ++ 2.0 and I would like to use it to measure the number of times a wheel turns, by means of a hal-effect probe (coming from a bike velocimeter), and send the measurement to a computer, where it will be used by an application I am programming.

I know very little about electronics so I am writing to seek guidance on how to begin, whether my intended approach will work or I should choose other components, what to read on, ...

If possible I would like to connect the probe directly to the teensy, avoiding any other component. I don't know about the voltage the probe will deliver or the shape of the signal, so I was planning to measure it using an osciloscope I have access to.

The wheel will be turning at a maximum of 25 revolutions per second and taking into account the size and position of the magnet and the probe I estimate a minimum "high signal time" of 0.4 ms, with the entire turn taking 40 ms.

I have been learning with the arduino IDE/teensyduino and that's the language I would like to use (I have no experience with C and I prefer learning about electronics than spending my time learning C).

So, the questions I have are:

- For measuring the signal from the probe, would I just connect it directly to the osciloscope or should I add some elements in between the two?

- I can imagine the probe will deliver a very low voltage. Will the teensy be able to detect the changes of that signal? If I understand the analog input correctly, it can roughly detect a 5 mV change, am I right?

- Is it safe/adequate to connect the probe directly to the teensy without any other element for this use?

- Any advice on how to do this or what to read on?

I have some doubts on the software side too, but I need to do some further reading and testing before posting those.

Thank you all in advance,

Pixe
 
If possible I would like to connect the probe directly to the teensy, avoiding any other component. I don't know about the voltage the probe will deliver or the shape of the signal, so I was planning to measure it using an osciloscope I have access to.

If there is any web page or datasheet about this part, you could post a link....

- For measuring the signal from the probe, would I just connect it directly to the osciloscope or should I add some elements in between the two?

Usually it's best to connect directly to the oscilloscope probe. If your probe can use 1X or 10X mode, usually 10X is best to avoid capacitively loading the signal (possibly changing it).

- I can imagine the probe will deliver a very low voltage. Will the teensy be able to detect the changes of that signal? If I understand the analog input correctly, it can roughly detect a 5 mV change, am I right?

Yes, using analogRead, and if the signal is free of substantial noise and interference.


- Is it safe/adequate to connect the probe directly to the teensy without any other element for this use?

- Any advice on how to do this or what to read on?

Impossible to give useful advice without the datasheet or technical info on this device.
 
Thank you for your quick reply Paul.

The probe is literally from a bike velocimeter, so I guess I will not be able to find a technical data sheet for it. I'll check that anyway.

I have the 1X/10X option in the osciloscope, so I will do as you suggest, but not until next week.

I'll come back with more information, some results and probably many more questions some time next week (I hope).

Thank you again.

Pixe
 
A very late update. After several months of inactivity I made the time to give the probe a second try. It turned out not to be a Hall effect probe but a reed switch, which is very simple to handle.

Thank you all anyway.

Pixe
 
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