Beginer needs help wiring Texas Inst. Opt 101 to Arduino Uno

Hi all,

I am a beginner, and, while I feel more confident figuring out the programming for my project, I have very little knowledge of electronics. Luckily, I believe what I am trying to make is incredibly simple, so I'm sure it will take no more than a few seconds of thought from many of you. I haven't been able to find an answer by searching the forum, at least not one that is simple enough for me to understand. Thanks for your patience with my lack of confidence with electronics! Here's a bit of background on my project, if that's helpful or interesting, but feel free to skip it.

Background on project:

I am trying to make a very simple infrared transmission density monitor (monitors how much light passes through an object) for monitoring the progressing density (basically opacity) of photographic film while it is submerged in developer fluid. I use the term "density monitor" rather than densitometer, because I have no ambition to make this thing actually give me objectively true info about density, but just a way of reliably repeating the process of film development until a certain density is reached on a strip of film with known exposure.

So I plan to use an IR emitter pointed directly at an IR sensor (face-to-face, as it were) just a few millimeters away, with the strip of film in between. I have done enough research to determine that the Texas Instruments Opt 101P is the right circuit to use to sense the transimitted IR light (Link to Mouser page: http://www.mouser.com/Search/ProductDetail.aspx?R=OPT101Pvirtualkey59500000virtualkey595-OPT101P; Link to data sheet: http://www.mouser.com/ds/2/405/sbbs002a-125738.pdf)

Plea for help!:

Partly because the TI Opt 101P is a circuit in itself with multiple components, I don't have the background to figure out how to wire it up to a simple Arduino Uno: how to supply it with the correct power and any other components that may be needed (like resistors), to understand what voltage should be supplied to it within the allowed range on the data sheet to get a good output resolution (or did I just totally invent that causal relationship?), and whether and how any other components are needed to get the output voltage to the correct range for a good sampling. Would there be different components, like different size resistors, to get the thing to work in the right range based on different intensities of light from the source?

Would someone be so kind as to walk me through setting this up? To be perfectly honest, I'm not even confident that I understand which pins are which on the TI product because of the technical symbols used in the data sheet.

I will be very grateful, and, if I can get this thing to work, I think it will be a very nice contribution to the analog photography forums I use, so many other people will have reason to thank you too!

Benjamin

Use the circuit in Figure 5 of the data sheet. Wire up the ground to the arduino ground, Vout to an analogue input and the supply to +5V.

Thanks for the help. I just found this posted in response to a similar question at http://forum.allaboutcircuits.com/threads/opt101.98154/:

"This is a fine old Burr-Brown part.
Connect ground (3 and 8) to ground.
Connect pin 1 through a 100 ohm resistor to +5V.
Connect a 100 uf capacitor from pin 1 to pin 3.
Connect a 0.1 uf ceramic capacitor from Pin 1 to pin 3
Connect pin 5 to pin 4.
Do not connect pin 2 to anything yet.

Connect pin 5 to an A-to-D converter input; the rest is up to your programming skills.

If the sensor is too sensitive, connect a resistor from pin 5 to pin 2. Try 100k, if its still too sensitive, reduce the resistor further.

If you are using a 3.3 volt power supply, the instructions above still apply, just substitute “3.3 volt” for “5 volt”"

Is it necessary to use the resistors and capacitors mentioned here? Or will it really work to just wire it straight in? Thanks again. It’s so nice people are willing to help out just to be nice!

Is it necessary to use the resistors and capacitors mentioned here?

Yes, I would use them all as shown in that Figure 5. They ensure the supply is correctly decoupled.

Ok thanks. I'm going to try to find a good intro to reading circuit diagrams online. It looks like something I could figure out, so I''ll do that and then post back if I have any remaining questions. Thank you again for the guidance. - Benjamin

Ok, so figure 5 says to use a 0.01 to 0.1 uf capacitor between pins 1 and 3. What I don't understand about the post I quote above is the 100uf capacitor that is also used:

"Connect a 100 uf capacitor from pin 1 to pin 3.
Connect a 0.1 uf ceramic capacitor from Pin 1 to pin 3"

Would you mind addressing this?

Secondly, there is no mention of a 100ohm resistor in series with the power input. What is this for? I know LEDs need current limited supply. Is this similar?

Thanks again.

Connect a 100 uf capacitor from pin 1 to pin 3.
Connect a 0.1 uf ceramic capacitor from Pin 1 to pin 3"

The small capacitor attenuates the high frequencies and the large one the low frequencies.
See:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

Secondly, there is no mention of a 100ohm resistor in series with the power input.

What figure in the data sheet are you talking about? Figure 5 does not have a "power input" pin 2 should be left unconnected, it is for adding extra bias on the photo diode when needed.