Is there a way how to measure ? - Page 1
Forum section: electronics / general

author: Jane
author_rank: Frequent Contributor
timestamp: October 21, 2014, 06:42:57 pm
content: As far as I understand proximity sensor in mobile phones works on a principle there is an emmitted IR coming out FROM proximity sensor and reflected IR comming TO proximity sensor. Is there any method how I can measure the emmited IR coming FROM the proximity sensor?Thank you for reply

author: SeanB
author_rank: Super Contributor
timestamp: October 21, 2014, 06:51:35 pm
content: Use another phone's camera to detect the light. That works quite well for me, and also works to check IR remote controls as well. It also works to detect IR light from fibre optic cabling, but does little other than showing there is light.

author: ve7xen
author_rank: Super Contributor
timestamp: October 21, 2014, 07:11:22 pm
content: It's very likely pulsed at low duty cycle. You need a phototransistor/photodiode - better if it's one in a case that only admits IR. You might need to seal outside light anyway. Optional bias circuit. You'll probably need an oscilloscope to catch the pulses.Calibrating an absolute measurement will be difficult.

author: Jane
author_rank: Frequent Contributor
timestamp: October 21, 2014, 08:04:43 pm
content: Thank you for the replies. Yes, I tried to use another phone's camera to detect the light but I could not see any light.( when using the camera with TV remote control , I can see the light, but not with proximity sensor). When does proximity sensor start to emmit the light? When someone is calling or only after I answer the call?And are you sure proximity sensors in cellphones really use IR light?

author: SeanB
author_rank: Super Contributor
timestamp: October 21, 2014, 08:40:45 pm
content: My android phone does, but only when you are actually in a call, it will be dark until the phone is in a mode where you will possibly be holding it against your ear, thus only in a call where you are not using the handsfree mode. It blinks the LED every few seconds to see if it has a reflection that it can sense.

author: Ryano
author_rank: Regular Contributor
timestamp: October 21, 2014, 09:39:00 pm
content: I have one of these for measuring such things.http://www.analysir.com/blog/2014/05/04/silver-bullet-oscilloscope-infrared-receiver/I also found this overview of infrared proximity sensing that might be helpful.http://www.eetimes.com/document.asp?doc_id=1272536If I have time tonight I'll fire up the scope, have someone call me, and see what I get!

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: October 21, 2014, 11:42:40 pm
content: Quote from: Jane on October 21, 2014, 06:42:57 pmI mocked up a photo resistor that was sensitive to IR light, a couple resistors for a voltage divider, a capacitor to filter DC and 2 AA batteries for the 3V source. Oh, and make one of the resistors a potentiometer so you adjust your output. You now have a wonderfully cheap IR light detector probe which can be connected to your scope to get all kinds of data from the IR source. If you calibrate it to a know IR value, it's fairly accurate too! Plus, any light source even from CFL, Incandescent and natural sources work too.

author: Jane
author_rank: Frequent Contributor
timestamp: October 22, 2014, 06:03:14 am
content: Thank you all of you for the replies.My problem is that after changing glass on a cellphone proximity does not work.So I think about that:The glass can be thicker than the original, or aperture(visors) are different , emmiting/receiving angle can be different or some other things.Any idea how to find out the reason? How to start that procedure and have a success? Thank you for help@Ryano: Did you have any time to check the proximity by using scope?

author: Ryano
author_rank: Regular Contributor
timestamp: October 22, 2014, 10:27:30 pm
content: I was able to get things set up, didn't have the time to do any experiments with the prox sensor. Hopefully I'll get a chance in the next few days.

author: miguelvp
author_rank: Super Contributor
timestamp: October 24, 2014, 02:35:02 am
content: Could it be capacitive? but then your hand will activate it as well and it probably does. But then a piece of wire will activate it too where a piece of something not capacitive will not, if it was IR then anything will activate it.