Proximity sensing - Page 1
Forum section: electronics / projects

author: timelessbeing
author_rank: Frequent Contributor
timestamp: March 23, 2018, 10:56:15 pm
content: Proximity activated stuff is pretty common. We've all walked through automatic doors. Public washrooms have them in them in the urinals, taps, soap dispensers and hand driers. How do they work? The driers usually have what looks like a piece of darkened glass, so I presume that it's optical (IR) based. Do they work in the dark? What other methods exist? Capacitive? Radar?I want to install some LED strip in my van that is activated when you wave your hand in front of a sensor, say within 15cm. It needs to be fairly immune to false readings. Are there inexpensive, easy to use ICs or cheap modules one could buy for this?

author: ogden
author_rank: Super Contributor
timestamp: March 23, 2018, 11:08:27 pm
content: Quote from: timelessbeing on March 23, 2018, 10:56:15 pmYes, IR sensors work in the dark. IR sensors are not that optical as you may think. Yes, for 15cm application you need IR sensor.QuoteCapacitive: usually hand driers and of course, capacitivetouchsensors everywhere including your smartphone, if any.Radar: mostly long-range, like automatic doors.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 23, 2018, 11:14:22 pm
content: IR is the most common as it's cheap and reliable for the sort of short ranges it's typically used for.They typically use near IR, either strength of reflection or triangulation.ST also do IR time-of-flight sensors initially aimed at phones etc. but also useable at longer ranges with more recent parts.The big advantage of TOF is measurement certainy - if you have a good enough signal, you know the proximity value has to be right, so good where you want to know the distance, or want triggering at a well-defined distance as opposed to a simple "there/not-there"Reflective sensors that use signal strength are much cheaper and simpler, but the signal varies a lot with target type - fine for washroom type applications where you just want a "there/not-there" indication at a fairly sort range.Ambient light is fairly easily excluded with a combination of optical filtering (Extremely effective with LED lighting which has minimal IR) and modulation to ignore DC ( daylight) and most artifical light.Capacitive is possible but has lots of issues, particularly noise pickup, that make it only useable in more niche cases where the environment is fairly predictable ( i.e. not anywhere that can be wet, or have wide variations in humidity, temperature, phase of the moon etc.)

author: timelessbeing
author_rank: Frequent Contributor
timestamp: March 23, 2018, 11:37:26 pm
content: This product doesn't appear to have any optical emitters/receivers or capacitive pads.http://www.klusdesign.com/products/show/177Quote from: ogden on March 23, 2018, 11:08:27 pmYou're referring to the film that lets us use our fingers with the smartphone, but you reminded me of something. My smartphone knows to turn the display on and off depending if I'm holding it up to my ear. Is it using the same capacitive film meant for fingers, or something else?

author: ogden
author_rank: Super Contributor
timestamp: March 23, 2018, 11:57:53 pm
content: Quote from: timelessbeing on March 23, 2018, 11:37:26 pmMobile phone "ear proximity sensor" usually is capacitive sensor as well. Other option is "RF loss" sensor, but honestly I don't (and don't want to) know how popular in mobile phones it is.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 24, 2018, 12:02:57 am
content: Quote from: timelessbeing on March 23, 2018, 11:37:26 pmCan't see a clear enough image but I think the square leadless device is probably an optical sensor

author: Paul Moir
author_rank: Frequent Contributor
timestamp: March 24, 2018, 12:16:58 am
content: Ultrasonic missing from the list. Good for a wide range of distance measurements but susceptible to interference. Cutting edge electronics are not required; this is how Polariod did autofocus in the early 80s. (Off topic, but how autofocus is done now is pretty neat.)Inductive for metal things not far away is super cheap and reliable.

author: timelessbeing
author_rank: Frequent Contributor
timestamp: March 24, 2018, 12:27:28 am
content: I found something promising on eBay.Advertised as "Infrared Reflective Photoelectric Switch IR Barrier Line Sensor Module TCRT5000L "It appears to have a pot and comparator to set a threshold, but is otherwise "dumb". ie. no modulation or filtering so it would need additional electronics.If anybody can think of any purpose designed ICs off the top of their heads I'm all ears.

author: ogden
author_rank: Super Contributor
timestamp: March 24, 2018, 12:36:16 am
content: Quote from: timelessbeing on March 24, 2018, 12:27:28 amIn my opinion seems to be good enough for your "up-to 15cm sense for van LED" application. Reading of TCRT5000L datasheet revealed that sensor range is 0.2 mm to 15 mm. Perhaps you have to pickanother sensorto get 15cm you need.

author: timelessbeing
author_rank: Frequent Contributor
timestamp: March 24, 2018, 12:50:10 am
content: Well I'll order one right away. I'm eager to test it out.Do you think it will be triggered by changes in daylight?Quote from: ogden on March 24, 2018, 12:36:16 amI noticed that too in the Vishay datasheet, but this is a Chinese knockoff. The item description says"from 2 to 30 cm adjustable"http://ebay.com/itm/192067056868

author: timelessbeing
author_rank: Frequent Contributor
timestamp: March 24, 2018, 01:19:30 am
content: I found something even better.Polulu Digital Distance Sensor 15cmhttps://www.pololu.com/product/2465It uses a Sharp GP2Y0D815Z0F sensor unit with an integrated signal processing IC.It has hysteresis , sunlight tolerance and bunch of other stuff.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 24, 2018, 08:15:52 am
content: Quote from: timelessbeing on March 24, 2018, 12:27:28 amSearch "proximity sensor" on Digikey

author: ogden
author_rank: Super Contributor
timestamp: March 24, 2018, 09:24:38 am
content: Quote from: timelessbeing on March 24, 2018, 12:50:10 amI have no idea. Particular sensor is designated for applications where direct or reflected sunlight is not possible. If you are concerned about interference then you would want to pick sensor which modulates IR

author: JJalling
author_rank: Unknown
timestamp: March 24, 2018, 12:30:05 pm
content: Quote from: mikeselectricstuff on March 24, 2018, 12:02:57 amLooks like VCNL4010 from Vishay (https://www.vishay.com/docs/83462/vcnl4010.pdf).BR Jonas

author: StillTrying
author_rank: Super Contributor
timestamp: March 24, 2018, 01:04:11 pm
content: A PIR sensor is a possible. At such short range no IR lens is needed, just mount the PIR sensor in a short ~15mm long shiny reflective tube.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 24, 2018, 04:16:58 pm
content: Quote from: StillTrying on March 24, 2018, 01:04:11 pmPIR detects motion, not proximity, and gives no meaningful distance or speed information - whether this matters depends on the application.

author: StillTrying
author_rank: Super Contributor
timestamp: March 24, 2018, 05:27:39 pm
content: Quote from: mikeselectricstuff on March 24, 2018, 04:16:58 pmYeah but, from the 1st post:"I want to install some LED strip in my van that is activated when you wave your hand in front of a sensor, say within 15cm. It needs to be fairly immune to false readings."

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 24, 2018, 07:25:28 pm
content: Quote from: StillTrying on March 24, 2018, 05:27:39 pmPIR probably won't work well as you can't really restrict the range, so likely to pick up stray motion unless it has a backstop.

author: timelessbeing
author_rank: Frequent Contributor
timestamp: March 24, 2018, 07:58:26 pm
content: Agreed. I think proximity detection will be less likely to activate unintentionally than motion detection.https://www.ebay.com/itm/222046677349$6 is reasonable