Proximity sensing using 3 IR LEDs

[adeel.sid]

Dear all

I am working on gesture control board that aims to detect motion direction of hand, e.g. from left to right or right to left.
For detecting direction, I decided to use a proximity sensor with three LEDs but having some interface problem.
the sensor is working fine with one IR LED but I am not sure how to MUX three IR LEDs and detect direction of motion on the basis of change of signal levels

Any suggestions?

 

[aashishsharma]

You need to compare the signals received from different emitters (3 in your case). Emitter IR light is reflected from object say hand then detected by proximity sensor. In order to differentiate between signals received from various emitters emitter are pulsed one after other. Read proximity sensor between each pulse. When object is near say 1st emitter it will receive more signal from that led. If the hand is moved say in one direction, the signal from one emitter will increase before the other. It is this time difference of signal strength that is analyzed to determine if a swipe gesture was made and in which
direction. I hope this helps
Aashish

 

[adeel.sid]

Thanks Aashish
Some more questions:

You mean I have to connect each IRLED output to GPIO pin of controller and then compare received signal
Is PWM signal works if I give to each IRLED?

It would be appreiciated could you provide some illustrative figure

 

[aashishsharma]

Thanks Aashish
Some more questions:

You mean I have to connect each IRLED output to GPIO pin of controller and then compare received signal

Yes
And you need to select sensor which you must be using. Vishay semiconducctor have development board for gesture recongnition you might wanna consult them. they are using VCNL4020.
this will help
**broken link removed**

 

[adeel.sid]

tht's the one I focus on but it doesnt use controller and I am trying to replicate through controller

 

[aashishsharma]

tht's the one I focus on but it doesnt use controller and I am trying to replicate through controller

Dont use the same thing exatctly. there is datasheet for the sensor that is mentioned in the link on the page i posted.
Go the application notes for the same. You will find sensor interfaced with I2C. You may use any controller that supports the protocol

 

[adeel.sid]

I have been reading vishay.com/docs/84218/vcnl4020gesturecontrolsensorboard.pdf
and know that I have to sense data from each IREDs one by one by using select lines of MUX but not sure how to set frequency of sel lines for this.

 

[D.A.(Tony)Stewart]

This is a difficult challenge. I have discovered "some" IR laser mice ( with red indicators) can sense hand waving at 3 meters, indicated by going out of sleep mode to active mode or slow pulse to fast pulse and placing mouse inverted on the floor. But to detect direction requires a differential and sum measurement of at least 2 laser or narrow beam 10deg proximity sensors used in mice

Since Mice focus is just at/below the surface, many mice will not work for long range, but some do,. It all depends on the optical splitter and lens. Then you would just need to use a dual beam emitter/detector with fixed location to detect with detector is stronger for motion direction feedback and sum of the two (or logical OR) for motion detection. The cleverness is in the optics.

In your case with 3 narrow emitters and one broad receiver can be sequenced for 1st reflections but you will get 2ndary reflections off walls and other things that will make it unreliable. Whereas independent Emitter/detectors sequenced or mux'd in TDM fashion can be synchronized with detection to determine the result.. COnsider a 6 stage Joihnson counter with interleaved off-states. Very narrow beam laser emitters with some beam spreading lens is required for Class 1 lasers . even 150mA narrow beam IR diodes can be hazardous.

In any case. reverse engineer Laser Mice for more ideas.

 

[adeel.sid]

Thanks for reply
Well, reliability may be compromised in my case as I have some other plan to tackle it.
What my focus is;
1. how to decide which IRED signal is detected among 3?
2. how to perform TDM (controller based or RC based?) and
3. how to control select lines of MUX (intend to use for IREDs)