Good light sensing chip? - Page 1
Forum section: electronics / projects

author: con-f-use
author_rank: Unknown
timestamp: May 19, 2014, 07:19:09 pm
content: After the blazing success of mysearch for a good temperature chipI wanted to give it a go again. First of all thanks to everyone who posted temperature thread two month ago!I want a generic, cheap and small solution to sense light. I want to buy it in a quantity of about a 1000 so I can use it in projects without thinking about it. Ideally it shouldn't take an ACD pin to read it with a micro, but that's not a hard requirement. I want it to differentiate between bright direct sunlight, indirect sunlight, rainy daylight, bright indoors, normal indoors, dim indoors, dark with open windows and no light.I realize you can sense the presence of light with just an led. That's the cheapest solution, if you use an opamp or your micro can measure mV. I want something a bit better.I really appreciate the experience of the members on this forum!What I have looked at so far:TEMT6000ALS-PT19-315CBH1750FVITSL12TTSL237S

author: denelec
author_rank: Regular Contributor
timestamp: May 19, 2014, 08:04:47 pm
content: CdS cells are light dependent resistors.They are very cheap (35¢ and up in quantity of 1000) and easy to use.http://www.digikey.com/product-detail/en/PDV-P8103/PDV-P8103-ND/480610But you will need an ADC input.And they contain cadmium. But according to Digikey, some are RoHS Compliant.

author: branadic
author_rank: Super Contributor
timestamp: May 19, 2014, 09:04:42 pm
content: QuoteOr at least a capacitor (NP0/C0G) to measure the (dis-)charge time with a microcontroller.

author: Paul Price
author_rank: Super Contributor
timestamp: May 19, 2014, 09:19:36 pm
content: You are asking a lot from only one device..too much. You need a photometer plus a spectrum analyzer to do what you want.A CdSe or CdS photoresistive sensor has a spectral profile similar to the human eye but doesn't give you spectral content of the light sensed, but a good overall measure of light intensity comparable to the human eye.Red, Green, Blue and UV LED's can function as photoelectric sensors that sense light in the same spectral frequency they emit.If you combine the information of the RGB + UV + Total light(CdS or CdSe)sensors you can create and calibrate( by making empirical measurements) a light sensing device that will exact the different lighting scenarios you want to detect. A MCU can be programmed to make a decision tree to compare stored measured sensor results versus the current sensor readings.For instance: Direct Sunlight has high UV plus high Total Light + balanced RGB.Sunlit Indoor light: Low UV Lower Total Light, Higher R and G than BlueIncandescent Lit Room: Very Low UV, High Red, medium Green, Low Blue, Medium Total Light

author: Ton
author_rank: Regular Contributor
timestamp: May 19, 2014, 09:27:47 pm
content: If you want a integrated version with I2C then something like this ? 73¢@1000pcs.http://www.digikey.com/product-detail/en/TSL25711FN/TSL25711-FNCT-ND/3095311used to use similar chips when working with mobile phones.Paul is right, for detecting your different scenarios, you need more than just the brightness of the light, and I guess we would be leaving the cheap area thenmy 2 centsTon

author: denelec
author_rank: Regular Contributor
timestamp: May 19, 2014, 11:09:33 pm
content: Quote from: Ton on May 19, 2014, 09:27:47 pmYou could use multiple sensors, each with different filters.

author: Stonent
author_rank: Super Contributor
timestamp: May 19, 2014, 11:56:48 pm
content: LEDs can sense light, not extremely well but you can actually light one LED by shining a really bright light on another.I've gotten cheap red LEDs to produce over a volt with my phone's camera flash.Metal can transistors can sense light also when you pop the top off.I have some Russian/Soviet transistors given to me by one of the guys on the forum that when you open the top and any light shines inside, the hfe just climbs continually without stopping.

author: SL4P
author_rank: Super Contributor
timestamp: May 20, 2014, 01:24:40 am
content: Quote from: con-f-use on May 19, 2014, 07:19:09 pmYou may be able to get away with a simple photo-transistor, CdS or other detector if you research and design a suitable 'aperture/barrel' to differentiate the different types of illumination. I've used a slot and/or tube approach with some success.Otherwise, filtering (both physical and signal) will add to your capabilities.To go all the way, a combination of these and digital processing is probably the only way you'll get close to repeatable, reference style of detection. A colleague has also used a linear CCD to detect variations - e.g. the presence of clouds.

author: DJ
author_rank: Unknown
timestamp: May 20, 2014, 01:34:02 am
content: The dynamic range of light is considerable. You may wish to use two sensors in a bridge, one shielded from light, the other exposed, to balance out drift/thermals.Likely cheaper in total to use a canned solution with I2C.

author: con-f-use
author_rank: Unknown
timestamp: May 20, 2014, 08:12:12 am
content: Well thanks again everyone!I'm just describing the ideal solution to me. I'm open to other suggestions. Of course the dynamic range is large and of course I might very possibly need an ADC input. I'm just asking for the chip that comes closest to my requirements and has the best value for money. Just trying to leech off of the experience of you guys.

author: Kjelt
author_rank: Super Contributor
timestamp: May 20, 2014, 08:46:18 am
content: Quote from: con-f-use on May 19, 2014, 07:19:09 pmThat is a large amount and the budget requirement is missing, what is your targetprice?If you look inside commercial combined movement, IR, light sensors then they almost all use a standard photoresistor pure for cost.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 20, 2014, 08:53:39 am
content: APDS9007 - logarithmic output, works over a 3 to 70klux rangehttp://www.mouser.com/ds/2/38/V02-0512EN-4985.pdf

author: fcb
author_rank: Super Contributor
timestamp: May 20, 2014, 10:41:30 am
content: For your 1000 qtyy, it's worth putting in a little bit of design work.I'd use a $0.30 photodiode and a little bit of analog circuitry (depending on the accuracy required, you might go for range switching). Something like the TEMD7000 or TEMD6200 would do the job.As far as not using an analog pin. You could get away with using the Photodiode leakage to charge a capacitor (low leakage), and time how long it takes for the pin to flip (then reset the capacitor by decking the uC pin). You'd have to calibrate it though.

author: lpc32
author_rank: Frequent Contributor
timestamp: May 20, 2014, 08:28:25 pm
content: BTW, in case it matters, LDRs are kinda slow. They probably take a few ms to respond.

author: con-f-use
author_rank: Unknown
timestamp: August 06, 2014, 11:42:17 am
content: I ended up buying the NOA1212. Very nice device for € 0.20 (at quantities of 100) but I have jet to test it thoroughly.Thank you all for your knowledge!

author: eneuro
author_rank: Super Contributor
timestamp: August 06, 2014, 02:00:25 pm
content: Quote from: con-f-use on August 06, 2014, 11:42:17 amIt is interesting, It looks like this NOA1212 ambient light sensor has similar spectral response to human eye with maximum at 540nm (green) wave lengthMaybe do you know or was able to teardown this thing during tests and figure out what response time of this sensor might be?I've found only power down/wake up times in its datasheetNOA1212 datasheet

author: con-f-use
author_rank: Unknown
timestamp: September 22, 2014, 05:08:34 pm
content: Sorry, I kinda forgot about your request. I did a quick test by mounting an LED on the chip and driving it at different frequencies. The NOA1212 was in high gain mode with no load capacitor and 8.2kOhm load resistance at 5V suply. It's not too good a measurement, but it might help. Remember this is an ambient light sensor, not a photo detector.

author: reportingsjr
author_rank: Contributor
timestamp: September 24, 2014, 08:23:11 pm
content: Even though you already found a chip I want to throw this one out there: the TCS34725. Made by ams who have some very interesting chips in their portfolio.Not in stock at mouser, but has some details:http://www.mouser.com/ProductDetail/ams/TCS34725FN/?qs=ECv0MKUHA8HkCOWi8XoeIw%3d%3dAdafruit also has a small breakout board for it:http://www.adafruit.com/products/1334It is $1.58 in 500 qty so not the cheapest. Does individual R, G, B, and white. Talks I2C and supposedly works up to 400kHz.If you want to see some other neat chips check out what ams has:http://ams.com/eng/Products