Any compact, but simple to solder digital light sensor? - Page 1
Forum section: electronics / beginners

author: LinuxHata
author_rank: Frequent Contributor
timestamp: October 08, 2023, 08:41:45 pm
content: Hello.Students want to assemble their own 32x32 pixels imaging sensor (b/w), for which they want to use something with direct digital output, like BH1750 or similar.But there are two issues - these BH1750 are very tiny to be soldered directly, but the modules they are being sold soldered on - are too large, so 32x32 pixel array will require a very large lens to cover them all.After some searching, I came to VEML7700, but maybe there are other, easier to solder, alternatives?They do not need very high resolution, speed or sensitivity - as this is an educational project, 8 bit resolution and 1 lux minimal illumination would be fully enough.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 09, 2023, 06:17:45 am
content: Maybe use ready made modules and a Fresnel lens instead of normal lens.Plastic sheets of Fresnel lens are very cheap in comparison with normal lens of the same size. They can be ordered in almost any size, even as big as 1 square meter or more. Beware that large Fresnel lens can easily set things on fire when put into direct sunlight.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 09, 2023, 05:39:30 pm
content: If you want to use a very small sensor then the easiest way is to get your board made. Pcbway or similar will knock up a batch of prototype pcbs- they'll solder the sensors on for you.Check out the Osram TSL2591. Reflow soldering is fairly simple to set up in a basic lab. There's certianly a learning experience to be had.If your fame rate is modest then you can DIY a sensor from matrix of phototransistors you only need a very small amount of support circuitry.eg TEPT5700 (3mm dia).A bunch of low cost phototransistors, an opamp or two, a few 4067 muxes, and an adc port.Too easy really!Far more edcuational than all that digital nonesense. As the man said, “Any idiot can count up to one.”

author: LinuxHata
author_rank: Frequent Contributor
timestamp: October 09, 2023, 07:59:47 pm
content: Thanks, they already have Fresnel lenses of various sizes and question was not "how to build a light sensor array" but "which compact, but easy to solder digital sensors are available", so let's please stay in that direction.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 09, 2023, 09:48:10 pm
content: Quote from: LinuxHata on October 09, 2023, 07:59:47 pmReally? Sounds rude. Bad day, or did I upset you with something?Quote from: LinuxHata on October 08, 2023, 08:41:45 pmSo your last comma there, before the word alternatives, was a typo? You were not looking for alternatives in building a sensor array? You were looking only for an easier to solder chip. OK, but then you shouldn't have put the comma before alternatives.

author: LinuxHata
author_rank: Frequent Contributor
timestamp: October 10, 2023, 04:54:53 am
content: I don't think you're moving discussion to the right direction.Question was asked very clearly, I don't know how to explain in more detail.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 10, 2023, 09:11:00 am
content: OK. Normal approach for selecting the sensor would be to google for 'ambient light sensor datasheet', then open the datasheets of each type, and see available package and/or footprint. Another starting point to get a collection of what's available might be your preferred distributor, e.g.https://www.arrow.com/en/categories/sensors/ambient-light-sensorshttps://www.digikey.com/en/products/filter/sensors-transducers/536Or ask a student to make a list of available footprints, then select together a good enough and in stock ALS.If the expected answer was 'use model x', then you should specify the soldering skill of the students, the soldering equipment, if it is in class or a homework, etc. Nobody can guess if the students are the members of a maker's club, university students, or maybe something else. But most of all, it's a forum, so expect discussions rather than a Q&A answer.The rest is personal advice (assuming your background is CS rather than EE), mostly pointing at drawbacks of an array of I2C light sensors. Please disregard if you already considered the following aspects.Whatever the sensor model will be, manually soldering 1000+ parts (32x32) of anything is a tedious task. It can take from hours to days, depending on skills and soldering equipment.A soldering oven would be the way to go. A soldering paste mask would speed things even more. I assume it has to be hand made, not ordered assembled, no pick'n'place machines, because otherwise would be easier to just use a ready made webcam as a sensor.I expect most sensors will beverysensitive regarding the temperature soldering profile, more than the average SMD part, so a low yield. You might need many tries to get the oven profile right.32x32 is very low resolution, yet 1024 individual sensors is a considerable big number to deal with one by one. For a 32x32 light sensor would be easier to use the sensor of an optical mouse. Most of them have a debug mode, where they can be read as a webcam, usually available by I2C. Mouse sensors are usually THT soldering 8...16 pins DIL, very easy to handle. If not on stock, buy a cheap optical mouse and take its sensor. Also, lens can be tiny, or even used with no lens, as a camera obscura.Another challenge in case of using individual sensors would be addressing 1024 sensors of the same type. Some sensors only allows fixed I2C addresses (or if not fixed, then a very small range of 2...8 distinct addresses only, because usually it's only one sensor on a given I2C bus).Another thing, when reading individual pixels, FPS might become very low, so low that rolling shutter effects would only make it good for still images.The only advantage I can see would be the extra resolution in light intensity.I would chose something more creative and less tedious. For example, a single pixel camera, with mechanical scanning. Or, with one light sensor and one accelerometer, so to be shaken by hand for scanning the scene, things like that. Either way good luck with the project.