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I am a new user to the TI 4305529 launchpad and I'm using Energia. 

I am trying to compose a program to determine the frequency of a cyclic signal. 


The signal will be generated by one of several methods

1 a magnet passing close to a pickup coil

2 a magnet passing close to a Hall Effect detector

3 an interrupted light beam


I'm not yet sure which one yet


What I need to know is the requirements on the input signal, 

Voltage levels 

wave forms , Square wave, Sinusoidal, 

output impedance of signal generator,

etc, etc.


Now I know this is a large question . I am looking for some help getting started.


By way of information I am a retired  Electrical Engineer, but of the PT era  (Pre Transistors). 

Bits were flat back then .  





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Hi @@Flatbits,


As you state in your post, there are lots of ways to go about this.  Here are a couple of ideas just to get you started...


1) Read the reflection of an infrared LED off of a target -  I used a cheap CNY70 to make a tachometer and posted some photos here: https://github.com/fmilburn3/Tachometer_CNY70/wiki .  The Energia code is here:  https://github.com/fmilburn3/Tachometer_CNY70/blob/master/Tachometer_CNY70.ino


2) Use a hall sensor and magnet - An example is this rainfall measurement device:  photos:  https://github.com/fmilburn3/Rainfall_Hall/wiki  code: https://github.com/fmilburn3/Rainfall_Hall/blob/master/Rainfall_Hall_Test.ino


3) Photointerrupter: https://github.com/fmilburn3/Photointerrupter_Sharp_GP1S53VJ000F. I also salvaged some out of an old printer along with the motors for speed control/measurement.  They work the same, just be careful to put a current limiting resistor on the diodes when you test them or you will likely burn them out. 


4) Reed Switch:  These are kind of fragile compared to the above but they are cheap and I have used them successfully.


In all of the above examples (all with a F5529 if I remember correctly) I used a continuous 3.3V input.  The output varies depending on the sensor and how you are using it.  For a reed switch it will be on or off.  I think on the CNY70 I used an analog read with the analog signal varying according to how strong the reflection is. You could also drive to on or off with an op amp There are a number of tutorials on this type stuff, usually for Arduinos.  They are simple devices and the code normally ports without a change.  Just remember that much of the Arduino stuff is 5V while the LaunchPad is 3.3V and handle accordingly.


The sensors above are inexpensive and it is fun just to get one of each and see what they do....



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This might be an idea.




I have bought some of these with a view to a future project.


Haven't started yet due to no free time.


They sell a reasonably priced adaptor kit and an expensive demo kit.


There's a library here.






Might be of use ...... Might not.





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Where the sensor will be mounted should be a design consideration and could help determine which sensor type to go with. High heat might mean Hall can't be used; oil / dusty environment might preclude optical. Electrical noise might cause issues as well.



Also, I noticed you mention a magnet passing a pickup coil. An alternative would be a variable reluctance sensor. These can sense ferrous metals passing by without the need to embed a magnet in some sort of trigger; they are commonly used in automotive and related applications where they might be subject to harsh conditions. Their downsides include a variable voltage output based on speed: low voltage at low speeds and higher voltage at higher speeds. They also require additional circuitry to properly condition the signal to something a microcontroller can interpret.


The other sensors might also require additional circuitry, but that would be dependent on the sensor itself as to what it would need.



AMS has a nice catalog of rotary position sensors like mentioned above. Allegro has a good selection of Hall effects some of which, if I remember, do not require embedding a magnet in the target trigger- they operate similarly to VR sensors detecting ferrous targets like teeth on gears or windowed wheels.

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