I need help identifying a smd component

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DeltaFaya

New Member
Hello,

I'm at work, and i have a task : someone gave me a small PCB and asked me to draw the schematic of it. The person who designed this PCB is not working anymore and he didn't left any single bit of information about that PCB.
So far, i've been able to understand, identify and draw pretty much everything, but i'm currently stuck : i can't identify this specific component (see picture). Even after searching with the marking on it, i can't find it's reference.


My guess is it is some kind of transistor, as it seems to be used to draw current for 4 LEDs. I draw the schematic linked to the component to help understand its role on the PCB :




So, if there is anyone who can work his magic to find that component, that would be awesome !

Thanks
 
Can you at least figure what the circuit boards purpose ave being ?

Do you have reasons to think the LED's may have being used to detect light rather than emitting light ?
 
Often SM device numbers are unidentifiable - but first off, what does the device do?, and specifically what do the LED's do?.

I'm presuming it's some kind of light or torch?, and the device is an NPN transistor switched ON via the 10K resistor (which I'd prefer to be considerably lower value), the 0.33 ohm is a current limiting resistor.

Assuming that's correct, it's pretty horribly and poorly designed - I'd short out the 0.33 ohm, lower the 10K considerably (depending on the current capability of the chip feeding it), and put a 0.68 ohm in series with each series pair of diodes.
 
The PBSS302NX transistor seems to be a high gain/darlington (Hfe > 500 typical), so the 10k to base might be alright.
 
I think Sagor1 is right about the PBSS302NX transistor, it fits quite well !

To give more information about the purpose of this PCB : it's a device supposed to detect neurotoxic gases, using light and liquid crystal. Some light is emitted using 4 LED, it goes throught a panel with some liquid crystal+some other chemical reacting to gases, and the residual light is collected with 4 photo-diode.
The DAC pin (pin 0) of the Seeeduino is used to drive and vary the intensity of the 4 LEDs using the NPN PBSS302NX transistor.
And we use 4 other pins of the Seeduino to "read" the 4 photo-diode (the 4 signals go throught a MAX9916 to amplify them).

This small device was a prototype, developped by a student for his PHD in optics.
 
So what happened to his thesis?, surely it was all clearly documented - or he was wasting his time

Incidentally, during my daughters Chemistry degree, they had to build an opamp circuit with an LDR, for measuring the amount of light passing through a liquid - sounds a similar-ish sort of thing.
 
Nigel Goodwin said:
So what happened to his thesis?, surely it was all clearly documented - or he was wasting his time
Click to expand...
Surely, his thesis it quite well documented and i have it ! Unfortunatly, the electronic part of it wasn't relevent to figure in it. So, all i have about that device is only the description of its fonctions, but that's all.

This student was assisted by an electronical engineer who retired since. He designed and made that PCB but he wasn't know for being tidy and for keeping clean documentations about his work

I wont be able to get everything "right" (i probably wont be able to find the ref of the LEDs and photodiodes), but the closer i am, the better.

I am currently making the schematic on OrCAD Capture. Once i'm done, i'll post it here, so you'll have the full picture
 

That's a shame - it wouldn't have taken much effort to add details of it to his thesis, presumably he must have had a reference to it?, but if that reference no longer exists it doesn't help.

Was it originally a 'one off' for his Phd?, and are you now wanting to manufacture a few of them?.

There are surprising crossovers between Chemistry and Electronics - in fact my daughter (with her Phd in Chemistry) works as a Technician at a University, for two different Physics based departments (plus her own research as well), but comes under the banner of "Electronics, Computing and Maths"
 
Well, his thesis was centered around optical physics so, the small part about the electronic wasn't important i guess.
The thesis is called (in French) : "Capteurs pour la détection de gaz neurotoxiques utilisant la transition d'ancrage de cristaux liquides". Which could be translated as : "Sensors for the detection of nerve gases using a liquid crystal anchoring transition."

The prototype i have was indeed a "one off" for his Phd, but we do not want to manufacture more.
As your daughter, i'm working as a Technician in electronic at a University in France, mainly for the Optical Physics department (and for some other departments). I'm newly arrived here, as i started one month ago only !
I don't think there is a "clear" purpose for me to re-draw and re-design that PCB other than having the schematic on hand if one day someone else need to work again on the project or another project using similar principles.
 

Here's Melissa's overview from her university pages:


So some sort of vaguely common optics theme going on here

I can't say I'm very clear about what she actually does?
 
So, if i made no mistakes, here is the full schematic of the PCB !

I have figured out everything, appart from the reference of the LEDs and photodiodes, and also the values of the capacitors as they're all CMS (so no marking). I'll have to mesure them later when i'll have the right equipment.

Thanks a lot for helping me figuring out the transistor !

 
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