DIY Arduino Exposure Meter

[joshgladstone]

Hey everyone, I wasn't sure if I should post this in here or the Exposure forum, but this seems more like the DIY type place.

So when I'm out taking photos and I need a meter, I usually walk around with an old GE PR-1, because it's a nice size and shape, and it works great. But it definitely has its limitations, especially with lower light levels. I've also got a Spectra IV for cine metering, but that's overkill to carry around in my pocket. I've also been getting into Arduinos a bit lately, and had purchased a cheap Pro Mini clone for a different project I had in mind. When I started playing with it, I began to wonder if I could make a small DIY light meter. I looked into the parts and it turned out the whole thing would be really inexpensive. So I gave it a shot!

It's called ƒLUX (for now), and it has a range of ISO settings from 1-6400, and shutter speeds from 1/3000 sec to 60 minutes, and cine speeds from 1-300fps (and of course I could always add more). It's still missing a couple of features that I want to add, and it needs to be assembled into a case, but it's close to done! Here's a video:


[video=youtube;2EB30AjOrN8]https://www.youtube.com/watch?v=2EB30AjOrN8[/video]


Comments and questions welcomed. Thanks!

Parts list:
Arudino Pro Mini clone (http://www.amazon.com/Estone-Version-Atmega328-Arduino-Compatible/)
Adafruit TSL2561 Light Sensor (http://www.adafruit.com/products/439)
64x128 OLED Display (http://www.amazon.com/gp/product/B00O2LLT30/ref=oh_aui_detailpage_o00_s00)
Rotary encoder with push button (http://www.amazon.com/gp/product/B00KHTLY7M)

 

[mexipike]

Awesome!

This looks great! I am always interested to see more diy projects especially with arduino. I really need to learn Arduino, I bought the arts and board to build the enlarger timer here but never really took the time to learn it. So many great opportunities and options!

 

[polyglot]

Good stuff. I love those OLED displays but I've not tried using one on arduino (just ARM). Where did you get the nice big font?

I think the best thing about the TSL2561 is that it has a separate IR sensor, so it might be (with some calibration and a short-pass filter) useful as a light-meter when shooting IR.

The light meter in my enlarger meter uses a TSL235R instead.

mexipike: let me know if you need any help with the build!

 

[joshgladstone]

Thanks for the kind words!

An IR-only mode is definitely one of those missing features I want to add. I can access the IR sensor easily enough, but it's hard to know how the values coming off the sensor relate to an exposure, especially since I don't have an IR-sensitive meter to test it against. But it's definitely something I'm going to try to implement.

And about the font size, that's part of the gfx and oled libraries provided by Adafruit. It's just scaling the letters up by factors of 2 or 3, but yeah it's included in the library. Except for the ƒ/ symbol. That's a bitmap image.

 

[DWThomas]

Very cool -- it's always a pleasure to see there are still people making things!

 

[Ashfaque]

I like it. Thanks for sharing. Please keep us posted on this nifty project of yours. I'd love to make one for myself.

Bests,

Ashfaque

Edit: If possible, can you please do a spoon-feeding version of the video? Say, from start to finish, with a list of all the tools and other things you need to make one, how to load the software, how to calibrate, etc.

 

[winterclock]

Is the code hosted somewhere?

 

[joshgladstone]

I haven't uploaded the code anywhere yet for a couple reasons. Mostly because I'm not done with it, but also because I'm not a programmer, so I feel like a lot of it is kind of hacky and that's sort of embarrassing? Especially the settings and menus and stuff. My wiring is probably iffy, too. I mean everything works, but I'm sure it's all done the wrong way. But yeah, once it's all finished I'll probably put it online somewhere. And I'll make a step by step build video, too.

 

[mrred]

I'm a programmer. Don't get self conscious about your code. Professionals often produce code that doesn't actually work, and yours does. There is a lot to be said for that.

 

[gittela]

I totally agree with mrred!
Get the code up, the best way to improve it is by feedback. I'm by no means a programmer but I still chuck my stuff up on github just in case someone wants to use and improve it.
Plus, I'm dying to make my own build of this!!

 

[grahamp]

It is a rare person who gets the software design and implementation right first time. There are always things worth refactoring. There are some seriously good tools available in the microprocessor world these days.

 

[joshgladstone]

Thanks everyone! I'm still not entirely sure what I want to do with it yet, but in all likelihood I'll open source everything once I'm finished with it. And of course I'll post updates here. Thanks!

 

[paul ron]

THats cool. BTW Radio Shack in my area is going out of business n selling everything 40%-60% off.... maybe a good time to shop for these componenets!

 

[joshgladstone]

Funny you mention it, I have a couple Radioshacks in my area, and they're both not going out of business, which is ridiculous. But I did drive by one just yesterday and got a ton of components at 70% off. The employee said "wow, longest receipt ever"

 

[franck]

Hello!

Really cool project, I was wondering if there were cheap and accurate light sensors usable to build a light meter. The TSL2561 seems to be a great option!

Any idea how to add flash metering capability? I guess that another light sensor and some circuitry is needed but I haven't looked into it.

Cheers,

Franck

 

[Photo Engineer]

Josh, I just lost our local RS as well, and I looted it as best I could before they closed. I got some great Arduino parts for our GEH process automation work. We are now trying to automate the emulsion making course for better results. I just ordered some pumps for under $10.

But, here is something that might interest you. There is now an R/G/B sensor that can tell you if your light is out of balance. Looks kind of interesting, but I lost the URL as usual as I had to go on and look at some other equipment for the automation project and I went too fast for my own good.

Anyhow, this sensor takes 3 "snapshots" of your subject and compares it to a "standard".

FYI.

PE

 

[Ashfaque]

Franck: If you planning to make one, then TSL2591 would probably be a better option as it has a wider lux range. I'm ordering both.

Ron: Are you talking about RGB Light Sensor - ISL29125 (SparkFun), or RGB Color Sensor with IR filter and White LED - TCS34725 (Adafruit)?

Best,

Ashfaque

 

[Photo Engineer]

It was neither of those. I wish I could find it again. It was a single sensor that sensed R/G/B in sequence and compared the voltage developed for each against a standard. It might have been Parallax or Vellman. I'll try to find it, but the ones you reference look interesting as well.

PE

 

[franck]

Franck: If you planning to make one, then TSL2591 would probably be a better option as it has a wider lux range. I'm ordering both.

Ashfaque

Thanks for the tip, I had not noticed that one

Cheers,

Franck

 

[joshgladstone]

Wow, I don't know how I missed those TSL2591s. Just ordered a couple! I'll have to rewrite some code to integrate them, but aside from that, all the coding is done and the meter is working great! And I've got a small 3d printer now, so I'm working on the case. Should be done really soon!!

 

[Ashfaque]

Great. Hope to see both versions of your codes and design soon.

While you're at it, you might as well get one or two updated TSL2561.

Nothing special though, just updating with a 3.3V regulator and level shifting circuitry for 3-5V power/logic microcontroller.

Bests,

Ashfaque

 

[Photo Engineer]

I should be banned from APUG. I just finished building a tiny digital camera with my Arduino. But then the pix are crap! That is the usual saving grace over analog which is always good!

PE

 

[Ashfaque]

While you're at it, you might as well get one or two updated TSL2561.

Nothing special though, just updating with a 3.3V regulator and level shifting circuitry for 3-5V power/logic microcontroller.

Bests,

Ashfaque

Ignore this ^. It was updated on 3 June, 2014, not 2015!

 

[Julia]

Couple things:
1. 2591 is indeed a better option but docs lack lux equation, ams not answering e-mails
2. big deal is optical window geometry and alignment, or the sensor will see too much of the scene, and angular sensitivity is nothing like we have in hand-helds
3. measurements still depend on spectra of the light source, separate equations are needed for fluorescent, sun, incandescent
3. I was to use a good luxmeter to solve the above

The reason I used those sensors: paired with wifi (ESP8266 instead of Arduino), made a dozen of those, simplifies light setup in a studio.

 

[jpentecost]

What a great project ! It would be really great to add a bulb ramper into a light-meter like this ..

Polaroid cameras had an auto exposure system (and I suspect other manufactures did something similar) Where there was a capacitor which was charged and when the button was pressed it opened the shutter, the capacitor then discharged via a light sensitive resistor. With lots of light it runs through quickly (short exposure) with a little light it goes through slower. With no light it just stays open until there is light. This is not very interesting as stills (it has some interest to to as you could do things like shoot a time exposure on the back ground and then turn on a light in the foreground and the shutter would close when it had enough light.) but in truth it's not particularly useful. I built a box that you could use with a Bolex that shot bulb exposures based on the front of a bastardised Polaroid (It "sort of" worked).

What is much more interesting is that Nizo added a function to their cameras called "AutonB" basically this was the same as the Polaroid system but worked as a TTL system on a cine camera. Basically as the light changed the exposure lengthened and shorterned so if you were shooting a night scene with cars travelling through it each frame would have the same amount of car activity regardless of the length of the exposure (so frame one where there were 20 cars passing in 5 seconds would be a 5 second exposure, if 20 cars pass in 20 seconds then it would be a 20 second exposure. etc)

You could adapt your meter to automatically shoot exposures from 1/5 sec to one min (depending on the lighting) with a camera that shoots using an electronic shutter release (like the EOS 1N) or if it's not a dirty word a 50 or 60D.