circuit explanation

[MRSSPOCK]

Could someone please give me an idea what is going on with this board design.
The board is from an old coffee machine.
The optical sensor is used to detect the presence of a linear ram.
I am just trying to understand the circuit, and figure out what that 3 pin black component is.
Can anyone give me some clues please.
I don't have access to the machine at the minute, but I do know tha pin 1 is 12V with respect to pin 3.

Here is the circuit diagram as I see it, and a photo of the actual board, with a couple of scribbles showing the optical sensor orientaion.
Is there a way to determine what diodes they are?
I get the 680 ohm resistor for the LED and the decoupling capacitor, but that's all.
Thanks

 

[IRstuff]

What do you want to know? It basically looks like U1 is a possible transistor pulling on pin3, depending on the optoisolator.

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[MRSSPOCK]

So, on the 5 pin connector, it appears pin 3 is a ground. and pin 5 is a ground too? Does that make sense? Then is the 47k a pull up resistor, and are the two diodes to provide a path to dump positive or negative spikes? Excuse my terminology if it's incorrect. This is not my field as I am sure have gathered. So then would pin 4 on the 5 pin connector be the actual high or low pin to indicate the presence of the ram?

 

[IRstuff]

I would assume, based on the limited information available, that pin 5 is a ground, but not necessarily the same ground as pin 3, possibly because they're on different systems. The 47k would be a pullup and the two diodes certainly look to be spike limiters and pin 4 would be an output signal.

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[MRSSPOCK]

Thanks for your reply. I never came across two separate grounds before on a board so that's what confused me.

 

[IRstuff]

There are pros and cons. Sometimes, the issue is that a ground might be noisy and specific circuits might need a much quieter ground to get their desired performance

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[MRSSPOCK]

So if that component is a transistor, does this image look sensible? If not could you edit the diagram please, and change to PNP if necessary. Thanks

 

[IRstuff]

That would be my assumption, but I would try to make some measurements before I made any rash moves.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[MRSSPOCK]

All sorted now and working well. Thanks for your input and for my education. Regards Mrs Leonard Nimoy