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1  Using Arduino / Project Guidance / Re: ADC - Board advice on: March 12, 2013, 09:14:42 am
The due and megagphave the most analogue inputs. There is only one A/D converter and these pins are switched inside the chip into it. As you have found you can use external multiplexers to switch any number of inputs you like to the A/D. Once inside the chip the analogue voltage is converted into a digital number between 0 and 1023 depending on the size of the voltage.

Thanks Mike,

I seem to remember someone pointing me towards you for some advice when I posted about this project last year.

That's exactly what I needed to know!

Simon
2  Using Arduino / Project Guidance / Re: ADC - Board advice on: March 12, 2013, 08:59:42 am
I've found a way of using analogue multiplexers, to place multiple analogue inputs into one adc, you access them via using a binary register, so each pin is looked at via the use of 001, 011.. 111 and all combinations between.

I don't want to buy a board and assume that because it has an analogue input, it can be converted to a digital output, or is that simply the case -if you place something analogue into the board on any of the pins; i see the due has 16 analogue inputs, will it simply run them through the ADC and give you a digital output?

basically aiming to map the light read of a photodiode and convert to to digital signal and then map for the creation of a grayscale image, the more inputs which convert to a digital signal I have, the more sensors I can use

3  Using Arduino / Project Guidance / ADC - Board advice on: March 12, 2013, 08:07:01 am
Hi guys,

I'm very new to all this so bare with me, i've been looking through the tech sheets but don't really understand the analogue to digital convertor.

I understand what one does, but basically, I want to put in multiple photodiodes into the board, which are analogue and gain a digital signal - what board would be best, i.e which has the most ADC's if they even have more than one.

Any help would be appreciated!

Simon
4  Using Arduino / LEDs and Multiplexing / Re: Multiplexing Photodiodes on: October 14, 2012, 06:21:30 pm
Thanks DC42, makes me feel a bit more at ease with what I'm planning on doing, sorry for the late reply, I have about, or exactly 16 other deadlines in the next 3 months before starting this so I'm a bit busy haha!

o_lampe, this sensors needs to fit within an existing camera system, it's all well and good recording light falling on an object, but the light that hits your screen from objects in a room wouldn't be focused (so i wouldn't worry - you'd be upside down too), and as light waves are destructive, you screen has anti glare technology, cheers for the brainstorming though, but I need complete control of the light here, so it's going in the back of something like this...

http://www.helixphoto.com/ebay/ProDigital/SinarP_4x5sn26285_1.jpg

Infact... you may of just saved me a load of time here o_lampe because i've just realise that these cameras are upside down and probably back to front, so I'll have to read bottom right to top left and then write the reverse - could make things fun...!
5  Using Arduino / LEDs and Multiplexing / Re: Multiplexing Photodiodes on: October 10, 2012, 05:59:19 pm
Cheers dhenry, I'll have a read.

CR: they're sensitive up to 820nm, from around 300, so more than enough.

Thanks for the input cr0sh, I'd need a hell of a lot more than that though I think, I suppose the other alternative is to use multiple arduino boards, each diode, or whatever I decide to end up using will act as a pixel to create a image/video - depending on which route I go down, hence why more is better.

I found out there is an electronics department which is combined with the computer science department at a different campus as part of my uni so going to try and have a meeting with them see if they can help me with the project, but cheers for all the input - it gives me an excellent start!
6  Using Arduino / LEDs and Multiplexing / Re: Multiplexing Photodiodes on: October 08, 2012, 07:25:14 pm
I'm not entirely sure as of yet, it depends on how fast the board can read of the data, I have access to a lot of lighting, doing a photographic science degree you see.

Flash duration syncs at 1/60th of a second, I can however use a continues light source, such as tungsten or even LED.

If you were talking about regard to the spectral power distribution of the light source, i plan to filter UV and IR so I am only dealing with the visible light spectrum.

7  Using Arduino / LEDs and Multiplexing / Re: Multiplexing Photodiodes on: October 08, 2012, 06:50:37 pm
Thanks CR, Will have a good read of that and try and get my head around it, I understand the programming aspect of it, but the schematics confuse me, as I said I'm very new to all of the electronic, but appreciate your help.

And dhenry, I started out with looking at LEds actually, they're much cheaper too, but people tend to like to argue the fact they're called a L Emitting d instead of actually thinking they can sense light too and help, what you said is interesting, you mention at the same time, does this mean the LED has to be lit when it is reading light, I'd assume that would then alter the read out?

I'll have a look into a photoresistor's though, thanks.

Also for this project I would be looking at getting as many sensing diodes into 5 x 4 inch area as possible, hopefully a few 100 as the more the better.
8  Using Arduino / LEDs and Multiplexing / Multiplexing Photodiodes on: October 08, 2012, 06:29:21 pm
Just wondering (and I am very very new to electronics) from what I have read about multiplexing, people do it a lot with LEDs can you do the same for photodiodes, and then return a digital output through the ADC?

If so using Arudnio, what would be the maximum amount I could then plug into the board and and gain an light intensity output for each individual diode?

Many thanks,

Simon
9  Using Arduino / Project Guidance / Re: Digital Camera Sensor on: August 19, 2012, 09:24:52 am
The reason I am designing from scatch is over the past two years of my degree we've done probably 30 different experiments on all different types of sensors, we study the science behind imgaging. This would be for my final project and I feel that they have tough us everything we need to know to be able to make it logically work - but they haven't taught us is how to actually put a sensor together and practically go through the proccess, only theory - so i thought it would be a good idea.

However like I said I have no knowledge of the electronics, thinking about it now, I don't actualy have to use flash lighting, I can shoot under constant light for a longer duration.

 John when you say 2k, would that be during the total time of the exicutable program or would I be able to, and if this is in the right terms, read a sensor, run it through the ADC, save the data and move onto the next sensor, but empty the sdram between?
10  Using Arduino / Project Guidance / Re: Digital Camera Sensor on: August 16, 2012, 09:35:27 am
Grumpy_Mike has some information on using LEDs as sensors - http://www.thebox.myzen.co.uk/Workshop/LED_Sensing.html

Yeah I seen that a littler earlier on, thanks.
11  Using Arduino / Project Guidance / Re: Digital Camera Sensor on: August 16, 2012, 09:31:27 am
No-one has yet said "it can't be done" for all values of "it", but LEDs are not designed to convert photons to current, so there is no particular attempt in the manufacturing process to make them so.
You're going to need a fair amount of amplification to do this, and that is going to be tricky and expensive in a large rectangular array, so the idea of making a linear array and scanning it either my moving the array, or by moving the image over it has a lot going for it.

See now that's an answer that helps me, I thought thats what an LED in a reading state did, it gave out a output voltage dependant on the input? (I am trying to read and understand this paper you gave me)

I understand a little bit more about what you mean by scanning, obviously that's not going to give me the 1/60th of a second I need, so it would have to be more like a cameras pixel area, 2D.

This is the sort of input sensor I was looking at:

http://uk.rs-online.com/web/p/photodiode/6548643/

Which has a very good spectral sensitivity to the visible light spectrum (and above) which I can filter out,

I can't find what sort of output that will give, but I assume it's just a voltage which I can measure and convert to a digital signal?


12  Using Arduino / Project Guidance / Re: Digital Camera Sensor on: August 16, 2012, 09:11:53 am
Do you believe that it would be better to try and sell you an unsuitable product?


That's not what I said, but I don't feel like i've been told enough of why it can't be done, to believe it.

I don't want to start an argument on a forum, it's stupid.



13  Using Arduino / Project Guidance / Re: Digital Camera Sensor on: August 16, 2012, 08:48:53 am
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I don't really understand what's going on here
Some background reading http://www.merl.com/papers/docs/TR2003-35.pdf


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surly that can be done afterwards with programming,
I'm rude, but you're surly. Let's call it quits   smiley-wink


Well lets hope the marketing department for the products don't rely on the moderators to sell them, cause you aren't doing a very good job.

Thanks for all your 'help'.
14  Using Arduino / Project Guidance / Re: Digital Camera Sensor on: August 16, 2012, 08:36:08 am
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somewhere between 1/60th and 1/125th of a second.
In which case, you're probably not in Arduino territory. Not single ones, anyway.
Do the simple arithmetic - 9600 (roughly) conversions per second says you'd need 1/10th of a second to do the readout.

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As for greyscale resolution, the minimum need for image detail is 16bit,
That's also blown you out without an external ADC, in which case, I don't see much need for an Arduino.
I think 16 bit for a LED is hugely optimistic.

Is 1/10th of a second not a realistic amount of time to take 900 readings? Like I said i've never really used this before, I thought programming wise that's a reasonable time to take the readings

Also, ADC, surly that can be done afterwards with programming, you just save the analog reading which the sensor gives and then convert it to it's digital pixel value dependant on where it was between it's top most and bottom most calibrated setting?

I don't really understand what's going on here, I'm asking for guidance and you seem to be going about it in a very rude way for some reason? This is something that I would like to do, I understand I can't do it on my own, I don't understand the hostility towards the project.
15  Using Arduino / Project Guidance / Re: Digital Camera Sensor on: August 16, 2012, 08:17:07 am
Exposure time is dependant on how long the flash duration lasts for, so for low powered lights, such as speed lights, can go very fast, if using studio lighting, somewhere between 1/60th and 1/125th of a second.

As for greyscale resolution, the minimum need for image detail is 16bit, It's just a case of programming conditional if statements and setting up hight and lower limits, i.e if returns between x and x then set greyscale level to x, all I know at the moment is it has to be 16bit minimum, but that's a programming area, which can be tested at a later date.

I'm interested in being able to at least be able to get information via the use of an Arduino board for now, no point thinking about anything else if it wont do it.





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