A simple circuit to read 3-400 pixels

Thread Starter

Vijay Rana

Joined Apr 3, 2019
6
Hi. I am working on a project where I want to read a an array of photoresistors/photodiodes. Similar to a CCD camera, but instead of a 1024x1024 chip I want to custom build an array of photodiodes or photoresistors (may be 2x400). I am very new to electronics would highly appreciate it if someone could point me in the right direction.
Thanks!!!
 

djsfantasi

Joined Apr 11, 2010
7,870
Hello!

We need to know where you want to go and how your getting there before we can point you in the right direction.

Basically, you’re going to have to supply a whole lot more information

Here are a few questions to get started
  • Why do you want to build a custom array? How is it going to be used?
  • What or how are you thinking of reading this custom array? With a discrete circuit or with a microprocessor? If the latter, which processor would you like to use?
  • What is being ‘scanned’? Will it be close to the array or from a distance? Which sensors you use might depend on your answer.
  • How many items may be scanned?
  • How fast will the scan need to be?
  • For what purpose is the overall project intended?
I could think of a few others, but my lunch just got set in front of me.
 

Thread Starter

Vijay Rana

Joined Apr 3, 2019
6
Hi
Why do you want to build a custom array? How is it going to be used?
i need my individual elements to be 3-5mm apart. I can collect the light from a large area and focus on to a CCD chip. But that would be more complicated for my needs. i want to measure the size of a rectangular light field. So the array will serve us a ruler for me, with each element representing a marking.

What or how are you thinking of reading this custom array? With a discrete circuit or with a microprocessor? If the latter, which processor would you like to use?
That was actually my question. I would prefer a microprocessor, but I don't know which one.

What is being ‘scanned’? Will it be close to the array or from a distance? Which sensors you use might depend on your answer.
I just want to see what array elements will be in the light field, and somehow separate them from the ones not in the field.

How many items may be scanned?
N/A

How fast will the scan need to be?
2-3s for the capture time and 2-3 s for readout

I could think of a few others, but my lunch just got set in front of me.
Hv a nice meal !!!
 

djsfantasi

Joined Apr 11, 2010
7,870
Hi



i need my individual elements to be 3-5mm apart. I can collect the light from a large area and focus on to a CCD chip. But that would be more complicated for my needs. i want to measure the size of a rectangular light field. So the array will serve us a ruler for me, with each element representing a marking.

That was actually my question. I would prefer a microprocessor, but I don't know which one.

I just want to see what array elements will be in the light field, and somehow separate them from the ones not in the field.
N/A

2-3s for the capture time and 2-3 s for readout

Hv a nice meal !!!
Thanks, it was good!

Have you any programming skills? IMHO, this screams microprocessor. My favorite is the Arduino. It has a shorter learning curve than others. But if you need to learn programming, maybe not.

Why are you using 2x400 sensors? Are you measuring light intensity along a line or are you going to scan the light field. Is the field 10mm*2000mm or 2M*2M?Related, how are the sensors going to measure intensity without blocking the light source?

With 800 sensors, you are also going to figure out how to address each one individually. This is not trivial. Is a field of 2M every 5mm really necessary. I’m asking, could you use a larger spacing? Say 10mm? (just as an example)?

If you used optics (a lense) to focus on a CCD chip, how are you going to read the chip?

See, there are many questions.
 

Thread Starter

Vijay Rana

Joined Apr 3, 2019
6
Thanks, it was good!

Have you any programming skills? IMHO, this screams microprocessor. My favorite is the Arduino. It has a shorter learning curve than others. But if you need to learn programming, maybe not.

Why are you using 2x400 sensors? Are you measuring light intensity along a line or are you going to scan the light field. Is the field 10mm*2000mm or 2M*2M?Related, how are the sensors going to measure intensity without blocking the light source?

With 800 sensors, you are also going to figure out how to address each one individually. This is not trivial. Is a field of 2M every 5mm really necessary. I’m asking, could you use a larger spacing? Say 10mm? (just as an example)?

If you used optics (a lense) to focus on a CCD chip, how are you going to read the chip?

See, there are many questions.
I am very comfortable with programming. I came across Arduino, and was trying to get thoughts on (electronics is not my strong point). My field is 50x50cm^2. I only need to measure the field dimension in 2 perpendicular directions. Ideally I would want to place a photodiode every 1 mm but, given the form factor, that may not be possible. So every 5 mm would work (160-200 elements should be good). Anything above 5mm will be an underkill.

I was thinking of using something like a bucket brigade circuit for read out, so now trying to figure out the electronics for that.

For a CCD chip, I could just buy a a small camera and get the images on my computer.
 

Alec_t

Joined Sep 17, 2013
12,253
If it were me doing this I'd consider using just one photo-sensor, X-Y scanned with a couple of RC servos.
 

AnalogKid

Joined Aug 1, 2013
9,395
Thinking of the output of the phototransistors - do you want to get a reading of relative light intensity, of just a simple above/below a threshold value? An above/below system would be much less complicated, because it is basically a 1 bit A/D converter.

ak
 

Thread Starter

Vijay Rana

Joined Apr 3, 2019
6
Thinking of the output of the phototransistors - do you want to get a reading of relative light intensity, of just a simple above/below a threshold value? An above/below system would be much less complicated, because it is basically a 1 bit A/D converter.
ak
Yeah, just HI vs LOW. I actually figured it out. Feeding 5V to a shift register through the PD should do the trick, I guess.
 

AnalogKid

Joined Aug 1, 2013
9,395
An 800 stage shift register is not a trivial thing, but if each transistor is biased so that it reads as a 0 or 1 at the light level you want, there are no obvious problems with the approach. Physically, you could make a small module with 8 phototransistors, one 8-in, serial out shift register chip (4014, 4021, etc.), and a 5 pin connector (serial data in, data out, power, clock, power, GND), and replicate it 99 times.

ak
 

Thread Starter

Vijay Rana

Joined Apr 3, 2019
6
An 800 stage shift register is not a trivial thing, but if each transistor is biased so that it reads as a 0 or 1 at the light level you want, there are no obvious problems with the approach. Physically, you could make a small module with 8 phototransistors, one 8-in, serial out shift register chip (4014, 4021, etc.), and a 5 pin connector (serial data in, data out, power, clock, power, GND), and replicate it 99 times.

ak
Yeah, that's the plan now. I would need only 400 elements though. Thanks!!!
 
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