UV light sensors with the 8/8/8

Technical Discussions on any InterfaceKits
Oxgernon

UV light sensors with the 8/8/8

Postby Oxgernon » Wed Jul 01, 2009 4:44 pm

Hello,


I need a sensor for ultra violet light (UVA and UVB, not UVC). Seeing that Phidgets doesn't have one, I searched around for one and found these:

http://www.advancedphotonix.com/ap_prod ... -G101A.pdf
http://www.advancedphotonix.com/ap_prod ... -G102B.pdf

One for UVA and one for UVB, which is okay, doesn't have to be both in one sensor.

Now, the question is, do you think these can be hooked up to the PhidgetInterfaceKit 8/8/8 and work?

According to the linked PDFs they should give a maximum reverse voltage of 5V so I'd guess they're compatible (unless I'm misunderstanding the term "reverse voltage", which is quite possible), but I notice they only have two connectors (anode and cathode), whereas the analog inputs on the Phidgets board have three connectors.

Sorry, I don't know much about the physics of electronics (I'm a programmer, not an engineer ;-P), but the way I understand it I would hook the anode to the power (red wire) and the cathode to the analog input (white wire) - but then what do I hook to ground (black wire)? Or isn't ground necessarily needed? Or am I just misunderstanding?


Thanks in advance for any help.


Kind regards,

Oxgernon

droswell

Re: UV light sensors with the 8/8/8

Postby droswell » Wed Jul 01, 2009 6:19 pm

Unfortunately, I think it's going to be more complex than that.

It appears this photodiode outputs a current instead of a voltage - the phidgets interface board (8/8/8) can only read analog voltage in. So what you have to do is create a small circuit to convert the output current from the sensor to a voltage level. Here's a short and sweet diagram:

http://soundlab.cs.princeton.edu/learni ... ode16.html

You're going to need one other component, an op amp, something like this: http://focus.ti.com/lit/an/sboa061/sboa061.pdf

along with some resistors / caps to make this work. The values of these components are approximated and can be calculated by knowing the sensor and op amp. Make sense?

Oxgernon

Re: UV light sensors with the 8/8/8

Postby Oxgernon » Thu Jul 02, 2009 3:52 am

Ah, I see - I thought it'd be too easy ;-)

Thank you very much for your reply.

I think building the circuit you mention is a bit out of my league (I don't even understand the schematics).

If I'm understanding you correctly, you're saying I need something that can turn a current into something the 8/8/8 can understand, right? Do you think the Phidgets 1122 - 30 Amp Current Sensor AC&DC could get the job done?


Thanks again,

Oxgernon

droswell

Re: UV light sensors with the 8/8/8

Postby droswell » Thu Jul 02, 2009 6:52 am

Ugh. I hate to be the bearer of bad news a second time...

The current sensor measures from -30 - 30 amps, in increments of roughly .06A. When it converts the analog signal to digital, think of it having a 10 bit long variable, so it can only store between 0-1024.

The sensor will be putting out current roughly between 0.0 and a max of 0.0000000001 A (1 nanoAmp!). If you're current sensor can only read in increments of 0.6A and your sensor current range is so small, you will never get a reading.

That sensor isn't really designed to stand alone - it needs a driver circuit to amplify it's output.

So you can always look for another sensor, or find an EE friend who needs some programming done!

Oxgernon

Re: UV light sensors with the 8/8/8

Postby Oxgernon » Thu Jul 02, 2009 9:44 am

Okay, I thought that might be the case ;-)

Been talking to one of the techies at work and he says he might be able to whip up the needed circuit for me, so I guess I'll see where that goes... Haven't been able to find other suitable sensors (the Vernier ones would be an option, but they're horribly expensive and kinda too big physically for what I need), but will have to poke around more if this doesn't work out I guess :-)

Again, thank you for your time :-)


Kind regards,

Oxgernon

Oxgernon

Re: UV light sensors with the 8/8/8

Postby Oxgernon » Thu Jul 02, 2009 11:03 am

Ah, I might have gotten a bit ahead of myself there... Had another search around and stumbled across this one:

http://www.scitec.uk.com/uvphotodiodes/ ... e_%231.pdf

As far as I can tell, this thing has three connectors like the Phidgets board, one for V+, one for ground, and one for signal... It provides an output voltage of 0-5V, and so should plug right into the Phidgets board as far as I can tell?

The only thing that looks "off" is that it requires an input voltage of 7-24V and as far as I understand, the Phidgets board only provides 5V... Would it somehow be possible to connect a regular 9V battery or a 12V powersupply to its input and still get the signal into the Phidgets board? And if so, would its ground connector go to the negative on the battery? Perhaps it could still run off the Phidgets board entirely, but would just provide a lower signal voltage, which I could calibraty myself out of?

Sorry, I'm really not good at this electronics stuff, bear with me if I'm rambling ;-)


This sensor is kinda pricey too, but it does have the needed amplifier built-in and comes in a very nice and small size. If it would work, it might be the best option rather than spend too much time and get frustrated in the end with another product ;-)


Kind regards,

Oxgernon

droswell

Re: UV light sensors with the 8/8/8

Postby droswell » Thu Jul 02, 2009 2:34 pm

Now that's a good looking sensor!

That should work, but yeah, you'll need an external DC 7-24 v supply. Something like a wall wart for a router or other device. Use a multimeter to determine the + side and connect that to the sensor ONLY. Connect the ground of your external supply to the ground on the sensor, AND the ground on the phidgets board. The signal out from the sensor goes to the signal in on the analog channel of the interface board.

Here's some mad visio skills to help visualize it:
http://www.screencast.com/t/WozJ4W6E

Make _SURE_ you do not connect the + of the supply to the interface board, or you will most likely get a smoke and/or light show.

Then you get to the part you'll enjoy - programming. Let us know how it works out.

Oxgernon

Re: UV light sensors with the 8/8/8

Postby Oxgernon » Thu Jul 02, 2009 4:15 pm

Excellent! :-)

I assume there's no risk connecting the ground of the power supply to the ground of the Phidgets board? Wouldn't want any smoke or explosions ;-)

I don't own a multimeter, but will see if I can borrow one since I don't really fancy having to buy one just for this... I was thinking about recycling an old power supply from an external harddrive enclosure I don't use anymore. It can provide both 12V and 5V according to the label and has two ground connectors as well, so I imagine this would work? Is "ground" just "ground" or might the 12V and 5V have separate "ground" connectors I need to be aware of? The label doesn't mention it so I'd assume not, but you never know... If that's a risk I guess I'd better just get the Phidgets 12V power supply when I order the rest of the stuff ;-)

I'll be sure to let you know how it all goes down the road, but the UV sensor thing is only a small part of a larger project (so large in fact that I think I'll need two 8/8/8 boards), so it may be a month or two before I have anything to show for my efforts... ;-)

Again, thank you very much for your time, you've been very helpful :-)


Kind regards,

Oxgernon

loco

Re: UV light sensors with the 8/8/8

Postby loco » Sun Jul 19, 2009 6:21 pm

hello,
I followed your diagram, but the power is confusing me. It looks like you have 2 ground pins, and one voltage out pin. In the phidgets 8/8/8, there are three pins ground, signal, and power. Where do these connect to in this op amp circuit?

sorry, i'm new to amplifiers.

thank you,
dave


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