Best Sensor for Fast Linear Motion Detection in Darkness, Compact Size (1/2 x 1/2)?

I'm new to electronics and working towards a project. I was hoping someone could help me choose the correct component for my constraints. I'd like to know what type of sensor I should be using. It needs to : Sense mechanical motion, a towards and away from motion to be more specific, be able to detect in complete darkness, hopefully be relatively small... say fit in a 1/2" by 1/2" space, but as small as possible is best, sense the motion which could be intermittent or move very quickly, say 800 movements per minute, be able to send the detection signal to a counter, which is counting down from a preset number, hopefully not consumer too much electricity so it could run from a cell or a battery. A good operating temperature range wouldn't hurt too, nothing extreme, just say what a human can handle.

The sensor would be fixed as well as the mechanical motion it is detecting. They would both be housed inside of an enclosure. The counter would be placed elsewhere in view and connected to receive signal. Ideally the sensor would be able to stand a shock such as being dropped without registering anything or breaking, as the complete package can be carried around by a person and not be affected by their movement or actions but still sense the mechanical motion in the object.

Is there a sensor that meets these constraints? I'm having a hard time piecing this together. I've done a few projects like a burglar alarm and human reaction timer, etc. but nothing purpose specific from scratch. Please point me in the right direction. Any help would be greatly appreciated!

Hi Jon,

You were asking for any sort of help, so here is my 2 cents! These are some ideas with the assumption you can use them, obviously you would choose (or not choose) any that fit your specs and liking.

If you can use a microcontroller (uC), do!

1) Sonar / ping sensor. The sonar sensor would ping some object at some distance and relay information about the distance/time from transmission to reception, either digitally or via analog.

If you need full analog, maybe find an analog sonar/ping sensor and feed the output to a schmitt trigger which will toggle your counter once the sensor sends a signal large (or small) enough indicating your machine met the distance requirement.

2) IR LED and IR photodetector. Have a coin cell size IR LED transmitter circuit on the moving part and an IR photodetector on the other side, at which your machine is moving toward and away from.

Follow the same procedure above to trigger your counter. This version might be more compact, but would also assume you have access to both sides of the machine and you would need to do some empirical tests.

If the machine that is moving forward and backward is facing something shiny (maybe put a mirror on it) you can put the transmitter and receiver right next to each other, but you need to make sure there is no cross/self talk directly from the transmitter to the receiver.

Each of these ideas could also incorporate an uC for ease of trigger level adjustment.

Hopefully this helps!

Max

Thanks Max! You've given me some good ideas to take to the drawing board and try to apply them to my project. I'm not sure if these will work for sure, I'm going to have to do a little homework and some testing. I really appreciate you taking the time to share your knowledge. If I can't apply these I may have to pick your brain later on! Thanks again!

Awesome! I am glad I could be of some help, please feel free to pick my brain, this project seems really interesting!

Hey Jon,

As size is critical you could use a hall effect sensor mounted inside the small space you have. Here is a link to one: http://uk.rs-online.com/web/p/hall-effect-sensors/2166231/
A small magnet can then be mounted on the moving part, the sensors output will then be proportional to the strength of the magnetic field. This output can go to a microprocessor to do the counting.

Something like an Arduino nano can be used: https://www.sparkfun.com/products/11113

Depending on how you construct your code you could read exactly how far away this moving part is. Although you don't mention needing this functionality. You could therefore write in a threshold state, so as to only count when it is close enough.

I don't mean to muddy the water! And I think you've already got some good options from Max, just always nice to have more!

Dan