Sensor to detect rotation

Thread Starter

128ITSH

Joined Jul 20, 2017
101
Hello everybody!
I am looking for a sensor that will be able to tell when a full rotation of a pointer which rotates inside a circle was completed.
The circle diameter is about 1 cm, and the sensor should have a distance of 0 to 1 cm from it. The pointer is red and also both the circle and pointer are protected by glass about 0.1 - 0.5 cm above them.
upload_2017-12-9_11-23-15.png
I understand I need a sort of color sensor, but which one? any help will be appreciated.
 

LesJones

Joined Jan 8, 2017
2,662
I would think almost any reflective opto sensor should work. The problem may be that there is as much reflection from the background as the pointer. You may have to paint the background matt black. You will find it dificult to find a sensor that detects a particular colour. Most sensors of this type use infra red light. This is an example of one type of sensor that would work.

Les.
 

Thread Starter

128ITSH

Joined Jul 20, 2017
101
I would think almost any reflective opto sensor should work. The problem may be that there is as much reflection from the background as the pointer. You may have to paint the background matt black. You will find it dificult to find a sensor that detects a particular colour. Most sensors of this type use infra red light. This is an example of one type of sensor that would work.

Les.
Thanks for your help!
I have no way to paint the pointer or background since they are covered in glass. Maybe an RGB sensor could do the job?
The sensor don't have to output an exact pulse when a rotation has completed, but show a difference in the data it outputs to an MCU when it sees the pointer so the MCU can handle it and convert it to a rotation.
 
Last edited:

bertus

Joined Apr 5, 2008
20,564
Hello,

Is there a height difference between the backgound and the pointer?
If so, a distance sensor might work.

Bertus
 

Thread Starter

128ITSH

Joined Jul 20, 2017
101
Hello,

Is there a height difference between the backgound and the pointer?
If so, a distance sensor might work.

Bertus
The pointer is almost touching the background and about 0.1cm higher than it. Can a relatively cheap sensor see this difference?
 

Danko

Joined Nov 22, 2017
931
Last edited:

Thread Starter

128ITSH

Joined Jul 20, 2017
101

AlbertHall

Joined Jun 4, 2014
9,999
What is the pointer and the background made of?
If the pointer is metal and the background isn't then you may be able to detect it with an inductive proximity sensor behind the background.
 

AlbertHall

Joined Jun 4, 2014
9,999
Second thoughts: Thinking this may be a utilities meter so you have no access to the inside.
Do you want to detect from the front through the glass or the back?
 

Danko

Joined Nov 22, 2017
931
I don't have any access to the pointer or to the background because they are covered with glass
Glue in parallel two plastic tubes 5 mm inner diameter, about half of inch long (two pieces of pen), it will like binoculars. On one end of this monster tube put to one hole blue LED, in other hole photodiod or phototransistor. Energize LED and point other end of monster tube to pointer. You will have changes of signal from photodiode when pointer travel under monster tube.
 

Thread Starter

128ITSH

Joined Jul 20, 2017
101
Second thoughts: Thinking this may be a utilities meter so you have no access to the inside.
Do you want to detect from the front through the glass or the back?
The pointer and background are both made from plastic. I want to detect this rotation from the front of the glass
Glue in parallel two plastic tubes 5 mm inner diameter, about half of inch long (two pieces of pen), it will like binoculars. On one end of this monster tube put to one hole blue LED, in other hole photodiod or phototransistor. Energize LED and point other end of monster tube to pointer. You will have changes of signal from photodiode when pointer travel under monster tube.
This solution sounds interesting but I don't fully understand it. Can you draw a simple schematic of it?
 

AlbertHall

Joined Jun 4, 2014
9,999
Does such sensor can tell the difference between red and white, or the difference of 1 mm height? Can you link me to a good par for this?
I expect there would be a good difference in the amount of light being reflected in each case. You may need to shield this kind of sensor from ambient light to maximise detection.
For instance: http://www.mouser.com/ds/2/427/tcrt1000-280041.pdf which is useable over a range of a few millimeters.
upload_2017-12-9_12-53-49.png
 
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