Why only 2.3 mA what's the point? Opto-Interrupter

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metron9
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Posted by metron9: Wed. Feb 8, 2012 - 01:04 AM
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I bought a bunch of these Opto interruptors for my CNC machine. I looked at the initial rating of 20mA as the current this little guy could pull down.

http://www.mpja.com/download/180...

After looking at page 4 I now see even at 30mA it only can sink 2mA. Not a very robust signal.

Is this part typically just used directly to a micro controller input pin that has an internal pull up?

I don't want to put a micro on every optical switch. I suppose I could add a small mosfet to the board and drive the gate with this thing but I did such a nice job routing all the little boards last night.

I even made a nice little mold to make a molded part that screws right to the machine. I used the little 3 pin servo wires for connectors.

I think I may just use IR led's and photo transistors to make my own parts.

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Learning and Information, General Electronics
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Kartman
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Posted by Kartman: Wed. Feb 8, 2012 - 02:59 AM
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Even with an opto transistor, you'll most likely need some amplification. In optos, this is referred to as the CTR (current transfer ratio). I'd suggest you choose an interrupter with receive electronics. Sharp comes to mind.

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LDEVRIES
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Posted by LDEVRIES: Wed. Feb 8, 2012 - 05:21 AM
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A uLN2804 or similar would do the interfacing nicely & sink 500mA.

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?

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metron9
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Posted by metron9: Wed. Feb 8, 2012 - 08:19 AM
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I was able to fit a 2N7000 without changing the size. I just modified it a tad again to make it easier to solder the fet and made a little more room for the pins. I am able to put two sets of pins male and female.

Since the fet is open now the line stays pulled up and I can connect them all in parallel or run separate wires. Typically there are 2 limit switches on each axes plus a third Home. 9 of these per machine.

All the limit switches will be connected to the estop line so any one of them can pull the line low. The way I had it I would have had to make another input box to monitor each switch and then pull the line low with a single fet.

The three home switches will be to center the X and Y axes as well as home the Z axes.

I typically use dead center as my start location for milling.

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